Merge "Remove wfRandomString() dependency in DatabaseBase"
[lhc/web/wiklou.git] / includes / db / Database.php
index 68df9cf..5d1078a 100644 (file)
@@ -1,5 +1,4 @@
 <?php
-
 /**
  * @defgroup Database Database
  *
  * @file
  * @ingroup Database
  */
+use Psr\Log\LoggerAwareInterface;
+use Psr\Log\LoggerInterface;
 
 /**
  * Database abstraction object
  * @ingroup Database
  */
-abstract class DatabaseBase implements IDatabase {
+abstract class DatabaseBase implements IDatabase, LoggerAwareInterface {
        /** Number of times to re-try an operation in case of deadlock */
        const DEADLOCK_TRIES = 4;
-
        /** Minimum time to wait before retry, in microseconds */
        const DEADLOCK_DELAY_MIN = 500000;
-
        /** Maximum time to wait before retry */
        const DEADLOCK_DELAY_MAX = 1500000;
 
+       /** How long before it is worth doing a dummy query to test the connection */
+       const PING_TTL = 1.0;
+       const PING_QUERY = 'SELECT 1 AS ping';
+
+       const TINY_WRITE_SEC = .010;
+       const SLOW_WRITE_SEC = .500;
+       const SMALL_WRITE_ROWS = 100;
+
+       /** @var string SQL query */
        protected $mLastQuery = '';
+       /** @var bool */
        protected $mDoneWrites = false;
+       /** @var string|bool */
        protected $mPHPError = false;
-
-       protected $mServer, $mUser, $mPassword, $mDBname;
+       /** @var string */
+       protected $mServer;
+       /** @var string */
+       protected $mUser;
+       /** @var string */
+       protected $mPassword;
+       /** @var string */
+       protected $mDBname;
+       /** @var array[] $aliases Map of (table => (dbname, schema, prefix) map) */
+       protected $tableAliases = [];
+       /** @var bool */
+       protected $cliMode;
 
        /** @var BagOStuff APC cache */
        protected $srvCache;
+       /** @var LoggerInterface */
+       protected $connLogger;
+       /** @var LoggerInterface */
+       protected $queryLogger;
+       /** @var callback Error logging callback */
+       protected $errorLogger;
 
        /** @var resource Database connection */
        protected $mConn = null;
+       /** @var bool */
        protected $mOpened = false;
 
-       /** @var callable[] */
+       /** @var array[] List of (callable, method name) */
        protected $mTrxIdleCallbacks = [];
-       /** @var callable[] */
+       /** @var array[] List of (callable, method name) */
        protected $mTrxPreCommitCallbacks = [];
-
+       /** @var array[] List of (callable, method name) */
+       protected $mTrxEndCallbacks = [];
+       /** @var callable[] Map of (name => callable) */
+       protected $mTrxRecurringCallbacks = [];
+       /** @var bool Whether to suppress triggering of transaction end callbacks */
+       protected $mTrxEndCallbacksSuppressed = false;
+
+       /** @var string */
        protected $mTablePrefix;
+       /** @var string */
        protected $mSchema;
+       /** @var integer */
        protected $mFlags;
-       protected $mForeign;
+       /** @var array */
        protected $mLBInfo = [];
+       /** @var bool|null */
        protected $mDefaultBigSelects = null;
+       /** @var array|bool */
        protected $mSchemaVars = false;
        /** @var array */
        protected $mSessionVars = [];
-
+       /** @var array|null */
        protected $preparedArgs;
-
+       /** @var string|bool|null Stashed value of html_errors INI setting */
        protected $htmlErrors;
-
+       /** @var string */
        protected $delimiter = ';';
 
        /**
@@ -80,7 +118,6 @@ abstract class DatabaseBase implements IDatabase {
         * @var int
         */
        protected $mTrxLevel = 0;
-
        /**
         * Either a short hexidecimal string if a transaction is active or ""
         *
@@ -88,7 +125,6 @@ abstract class DatabaseBase implements IDatabase {
         * @see DatabaseBase::mTrxLevel
         */
        protected $mTrxShortId = '';
-
        /**
         * The UNIX time that the transaction started. Callers can assume that if
         * snapshot isolation is used, then the data is *at least* up to date to that
@@ -98,10 +134,8 @@ abstract class DatabaseBase implements IDatabase {
         * @see DatabaseBase::mTrxLevel
         */
        private $mTrxTimestamp = null;
-
        /** @var float Lag estimate at the time of BEGIN */
-       private $mTrxSlaveLag = null;
-
+       private $mTrxReplicaLag = null;
        /**
         * Remembers the function name given for starting the most recent transaction via begin().
         * Used to provide additional context for error reporting.
@@ -110,7 +144,6 @@ abstract class DatabaseBase implements IDatabase {
         * @see DatabaseBase::mTrxLevel
         */
        private $mTrxFname = null;
-
        /**
         * Record if possible write queries were done in the last transaction started
         *
@@ -118,7 +151,6 @@ abstract class DatabaseBase implements IDatabase {
         * @see DatabaseBase::mTrxLevel
         */
        private $mTrxDoneWrites = false;
-
        /**
         * Record if the current transaction was started implicitly due to DBO_TRX being set.
         *
@@ -126,34 +158,44 @@ abstract class DatabaseBase implements IDatabase {
         * @see DatabaseBase::mTrxLevel
         */
        private $mTrxAutomatic = false;
-
        /**
         * Array of levels of atomicity within transactions
         *
         * @var array
         */
        private $mTrxAtomicLevels = [];
-
        /**
         * Record if the current transaction was started implicitly by DatabaseBase::startAtomic
         *
         * @var bool
         */
        private $mTrxAutomaticAtomic = false;
-
        /**
         * Track the write query callers of the current transaction
         *
         * @var string[]
         */
        private $mTrxWriteCallers = [];
-
        /**
-        * Track the seconds spent in write queries for the current transaction
-        *
-        * @var float
+        * @var float Seconds spent in write queries for the current transaction
         */
        private $mTrxWriteDuration = 0.0;
+       /**
+        * @var integer Number of write queries for the current transaction
+        */
+       private $mTrxWriteQueryCount = 0;
+       /**
+        * @var float Like mTrxWriteQueryCount but excludes lock-bound, easy to replicate, queries
+        */
+       private $mTrxWriteAdjDuration = 0.0;
+       /**
+        * @var integer Number of write queries counted in mTrxWriteAdjDuration
+        */
+       private $mTrxWriteAdjQueryCount = 0;
+       /**
+        * @var float RTT time estimate
+        */
+       private $mRTTEstimate = 0.0;
 
        /** @var array Map of (name => 1) for locks obtained via lock() */
        private $mNamedLocksHeld = [];
@@ -173,9 +215,183 @@ abstract class DatabaseBase implements IDatabase {
         */
        protected $allViews = null;
 
+       /** @var float UNIX timestamp */
+       protected $lastPing = 0.0;
+
+       /** @var int[] Prior mFlags values */
+       private $priorFlags = [];
+
+       /** @var Profiler */
+       protected $profiler;
        /** @var TransactionProfiler */
        protected $trxProfiler;
 
+       /**
+        * Constructor.
+        *
+        * FIXME: It is possible to construct a Database object with no associated
+        * connection object, by specifying no parameters to __construct(). This
+        * feature is deprecated and should be removed.
+        *
+        * IDatabase classes should not be constructed directly in external
+        * code. DatabaseBase::factory() should be used instead.
+        *
+        * @param array $params Parameters passed from DatabaseBase::factory()
+        */
+       function __construct( array $params ) {
+               $server = $params['host'];
+               $user = $params['user'];
+               $password = $params['password'];
+               $dbName = $params['dbname'];
+               $flags = $params['flags'];
+
+               $this->mSchema = $params['schema'];
+               $this->mTablePrefix = $params['tablePrefix'];
+
+               $this->cliMode = isset( $params['cliMode'] )
+                       ? $params['cliMode']
+                       : ( PHP_SAPI === 'cli' );
+
+               $this->mFlags = $flags;
+               if ( $this->mFlags & DBO_DEFAULT ) {
+                       if ( $this->cliMode ) {
+                               $this->mFlags &= ~DBO_TRX;
+                       } else {
+                               $this->mFlags |= DBO_TRX;
+                       }
+               }
+
+               $this->mSessionVars = $params['variables'];
+
+               $this->srvCache = isset( $params['srvCache'] )
+                       ? $params['srvCache']
+                       : new HashBagOStuff();
+
+               $this->profiler = isset( $params['profiler'] )
+                       ? $params['profiler']
+                       : Profiler::instance(); // @TODO: remove global state
+               $this->trxProfiler = isset( $params['trxProfiler'] )
+                       ? $params['trxProfiler']
+                       : new TransactionProfiler();
+               $this->connLogger = isset( $params['connLogger'] )
+                       ? $params['connLogger']
+                       : new \Psr\Log\NullLogger();
+               $this->queryLogger = isset( $params['queryLogger'] )
+                       ? $params['queryLogger']
+                       : new \Psr\Log\NullLogger();
+
+               if ( $user ) {
+                       $this->open( $server, $user, $password, $dbName );
+               }
+       }
+
+       /**
+        * Given a DB type, construct the name of the appropriate child class of
+        * IDatabase. This is designed to replace all of the manual stuff like:
+        *    $class = 'Database' . ucfirst( strtolower( $dbType ) );
+        * as well as validate against the canonical list of DB types we have
+        *
+        * This factory function is mostly useful for when you need to connect to a
+        * database other than the MediaWiki default (such as for external auth,
+        * an extension, et cetera). Do not use this to connect to the MediaWiki
+        * database. Example uses in core:
+        * @see LoadBalancer::reallyOpenConnection()
+        * @see ForeignDBRepo::getMasterDB()
+        * @see WebInstallerDBConnect::execute()
+        *
+        * @since 1.18
+        *
+        * @param string $dbType A possible DB type
+        * @param array $p An array of options to pass to the constructor.
+        *    Valid options are: host, user, password, dbname, flags, tablePrefix, schema, driver
+        * @return IDatabase|null If the database driver or extension cannot be found
+        * @throws InvalidArgumentException If the database driver or extension cannot be found
+        */
+       final public static function factory( $dbType, $p = [] ) {
+               global $wgCommandLineMode;
+
+               $canonicalDBTypes = [
+                       'mysql' => [ 'mysqli', 'mysql' ],
+                       'postgres' => [],
+                       'sqlite' => [],
+                       'oracle' => [],
+                       'mssql' => [],
+               ];
+
+               $driver = false;
+               $dbType = strtolower( $dbType );
+               if ( isset( $canonicalDBTypes[$dbType] ) && $canonicalDBTypes[$dbType] ) {
+                       $possibleDrivers = $canonicalDBTypes[$dbType];
+                       if ( !empty( $p['driver'] ) ) {
+                               if ( in_array( $p['driver'], $possibleDrivers ) ) {
+                                       $driver = $p['driver'];
+                               } else {
+                                       throw new InvalidArgumentException( __METHOD__ .
+                                               " type '$dbType' does not support driver '{$p['driver']}'" );
+                               }
+                       } else {
+                               foreach ( $possibleDrivers as $posDriver ) {
+                                       if ( extension_loaded( $posDriver ) ) {
+                                               $driver = $posDriver;
+                                               break;
+                                       }
+                               }
+                       }
+               } else {
+                       $driver = $dbType;
+               }
+               if ( $driver === false ) {
+                       throw new InvalidArgumentException( __METHOD__ .
+                               " no viable database extension found for type '$dbType'" );
+               }
+
+               // Determine schema defaults. Currently Microsoft SQL Server uses $wgDBmwschema,
+               // and everything else doesn't use a schema (e.g. null)
+               // Although postgres and oracle support schemas, we don't use them (yet)
+               // to maintain backwards compatibility
+               $defaultSchemas = [
+                       'mssql' => 'get from global',
+               ];
+
+               $class = 'Database' . ucfirst( $driver );
+               if ( class_exists( $class ) && is_subclass_of( $class, 'IDatabase' ) ) {
+                       // Resolve some defaults for b/c
+                       $p['host'] = isset( $p['host'] ) ? $p['host'] : false;
+                       $p['user'] = isset( $p['user'] ) ? $p['user'] : false;
+                       $p['password'] = isset( $p['password'] ) ? $p['password'] : false;
+                       $p['dbname'] = isset( $p['dbname'] ) ? $p['dbname'] : false;
+                       $p['flags'] = isset( $p['flags'] ) ? $p['flags'] : 0;
+                       $p['variables'] = isset( $p['variables'] ) ? $p['variables'] : [];
+                       $p['tablePrefix'] = isset( $p['tablePrefix'] ) ? $p['tablePrefix'] : '';
+                       if ( !isset( $p['schema'] ) ) {
+                               $p['schema'] = isset( $defaultSchemas[$dbType] ) ? $defaultSchemas[$dbType] : null;
+                       }
+                       $p['foreign'] = isset( $p['foreign'] ) ? $p['foreign'] : false;
+                       $p['cliMode'] = $wgCommandLineMode;
+
+                       $conn = new $class( $p );
+                       if ( isset( $p['connLogger'] ) ) {
+                               $conn->connLogger = $p['connLogger'];
+                       }
+                       if ( isset( $p['queryLogger'] ) ) {
+                               $conn->queryLogger = $p['queryLogger'];
+                       }
+                       if ( isset( $p['errorLogger'] ) ) {
+                               $conn->errorLogger = $p['errorLogger'];
+                       } else {
+                               $conn->errorLogger = [ MWExceptionHandler::class, 'logException' ];
+                       }
+               } else {
+                       $conn = null;
+               }
+
+               return $conn;
+       }
+
+       public function setLogger( LoggerInterface $logger ) {
+               $this->queryLogger = $logger;
+       }
+
        public function getServerInfo() {
                return $this->getServerVersion();
        }
@@ -269,12 +485,6 @@ abstract class DatabaseBase implements IDatabase {
                }
        }
 
-       /**
-        * Set a lazy-connecting DB handle to the master DB (for replication status purposes)
-        *
-        * @param IDatabase $conn
-        * @since 1.27
-        */
        public function setLazyMasterHandle( IDatabase $conn ) {
                $this->lazyMasterHandle = $conn;
        }
@@ -288,17 +498,6 @@ abstract class DatabaseBase implements IDatabase {
                return $this->lazyMasterHandle;
        }
 
-       /**
-        * @return TransactionProfiler
-        */
-       protected function getTransactionProfiler() {
-               if ( !$this->trxProfiler ) {
-                       $this->trxProfiler = new TransactionProfiler();
-               }
-
-               return $this->trxProfiler;
-       }
-
        /**
         * @param TransactionProfiler $profiler
         * @since 1.27
@@ -393,8 +592,26 @@ abstract class DatabaseBase implements IDatabase {
                );
        }
 
-       public function pendingWriteQueryDuration() {
-               return $this->mTrxLevel ? $this->mTrxWriteDuration : false;
+       public function pendingWriteQueryDuration( $type = self::ESTIMATE_TOTAL ) {
+               if ( !$this->mTrxLevel ) {
+                       return false;
+               } elseif ( !$this->mTrxDoneWrites ) {
+                       return 0.0;
+               }
+
+               switch ( $type ) {
+                       case self::ESTIMATE_DB_APPLY:
+                               $this->ping( $rtt );
+                               $rttAdjTotal = $this->mTrxWriteAdjQueryCount * $rtt;
+                               $applyTime = max( $this->mTrxWriteAdjDuration - $rttAdjTotal, 0 );
+                               // For omitted queries, make them count as something at least
+                               $omitted = $this->mTrxWriteQueryCount - $this->mTrxWriteAdjQueryCount;
+                               $applyTime += self::TINY_WRITE_SEC * $omitted;
+
+                               return $applyTime;
+                       default: // everything
+                               return $this->mTrxWriteDuration;
+               }
        }
 
        public function pendingWriteCallers() {
@@ -405,247 +622,80 @@ abstract class DatabaseBase implements IDatabase {
                return $this->mOpened;
        }
 
-       public function setFlag( $flag ) {
-               $this->mFlags |= $flag;
-       }
-
-       public function clearFlag( $flag ) {
-               $this->mFlags &= ~$flag;
-       }
-
-       public function getFlag( $flag ) {
-               return !!( $this->mFlags & $flag );
-       }
-
-       public function getProperty( $name ) {
-               return $this->$name;
-       }
-
-       public function getWikiID() {
-               if ( $this->mTablePrefix ) {
-                       return "{$this->mDBname}-{$this->mTablePrefix}";
-               } else {
-                       return $this->mDBname;
+       public function setFlag( $flag, $remember = self::REMEMBER_NOTHING ) {
+               if ( $remember === self::REMEMBER_PRIOR ) {
+                       array_push( $this->priorFlags, $this->mFlags );
                }
+               $this->mFlags |= $flag;
        }
 
-       /**
-        * Return a path to the DBMS-specific SQL file if it exists,
-        * otherwise default SQL file
-        *
-        * @param string $filename
-        * @return string
-        */
-       private function getSqlFilePath( $filename ) {
-               global $IP;
-               $dbmsSpecificFilePath = "$IP/maintenance/" . $this->getType() . "/$filename";
-               if ( file_exists( $dbmsSpecificFilePath ) ) {
-                       return $dbmsSpecificFilePath;
-               } else {
-                       return "$IP/maintenance/$filename";
+       public function clearFlag( $flag, $remember = self::REMEMBER_NOTHING ) {
+               if ( $remember === self::REMEMBER_PRIOR ) {
+                       array_push( $this->priorFlags, $this->mFlags );
                }
+               $this->mFlags &= ~$flag;
        }
 
-       /**
-        * Return a path to the DBMS-specific schema file,
-        * otherwise default to tables.sql
-        *
-        * @return string
-        */
-       public function getSchemaPath() {
-               return $this->getSqlFilePath( 'tables.sql' );
-       }
-
-       /**
-        * Return a path to the DBMS-specific update key file,
-        * otherwise default to update-keys.sql
-        *
-        * @return string
-        */
-       public function getUpdateKeysPath() {
-               return $this->getSqlFilePath( 'update-keys.sql' );
-       }
-
-       /**
-        * Get information about an index into an object
-        * @param string $table Table name
-        * @param string $index Index name
-        * @param string $fname Calling function name
-        * @return mixed Database-specific index description class or false if the index does not exist
-        */
-       abstract function indexInfo( $table, $index, $fname = __METHOD__ );
-
-       /**
-        * Wrapper for addslashes()
-        *
-        * @param string $s String to be slashed.
-        * @return string Slashed string.
-        */
-       abstract function strencode( $s );
-
-       /**
-        * Constructor.
-        *
-        * FIXME: It is possible to construct a Database object with no associated
-        * connection object, by specifying no parameters to __construct(). This
-        * feature is deprecated and should be removed.
-        *
-        * DatabaseBase subclasses should not be constructed directly in external
-        * code. DatabaseBase::factory() should be used instead.
-        *
-        * @param array $params Parameters passed from DatabaseBase::factory()
-        */
-       function __construct( array $params ) {
-               global $wgDBprefix, $wgDBmwschema, $wgCommandLineMode;
-
-               $this->srvCache = ObjectCache::getLocalServerInstance( 'hash' );
-
-               $server = $params['host'];
-               $user = $params['user'];
-               $password = $params['password'];
-               $dbName = $params['dbname'];
-               $flags = $params['flags'];
-               $tablePrefix = $params['tablePrefix'];
-               $schema = $params['schema'];
-               $foreign = $params['foreign'];
-
-               $this->mFlags = $flags;
-               if ( $this->mFlags & DBO_DEFAULT ) {
-                       if ( $wgCommandLineMode ) {
-                               $this->mFlags &= ~DBO_TRX;
-                       } else {
-                               $this->mFlags |= DBO_TRX;
-                       }
-               }
-
-               $this->mSessionVars = $params['variables'];
-
-               /** Get the default table prefix*/
-               if ( $tablePrefix === 'get from global' ) {
-                       $this->mTablePrefix = $wgDBprefix;
-               } else {
-                       $this->mTablePrefix = $tablePrefix;
+       public function restoreFlags( $state = self::RESTORE_PRIOR ) {
+               if ( !$this->priorFlags ) {
+                       return;
                }
 
-               /** Get the database schema*/
-               if ( $schema === 'get from global' ) {
-                       $this->mSchema = $wgDBmwschema;
+               if ( $state === self::RESTORE_INITIAL ) {
+                       $this->mFlags = reset( $this->priorFlags );
+                       $this->priorFlags = [];
                } else {
-                       $this->mSchema = $schema;
+                       $this->mFlags = array_pop( $this->priorFlags );
                }
-
-               $this->mForeign = $foreign;
-
-               if ( isset( $params['trxProfiler'] ) ) {
-                       $this->trxProfiler = $params['trxProfiler']; // override
-               }
-
-               if ( $user ) {
-                       $this->open( $server, $user, $password, $dbName );
-               }
-       }
-
-       /**
-        * Called by serialize. Throw an exception when DB connection is serialized.
-        * This causes problems on some database engines because the connection is
-        * not restored on unserialize.
-        */
-       public function __sleep() {
-               throw new MWException( 'Database serialization may cause problems, since ' .
-                       'the connection is not restored on wakeup.' );
        }
 
-       /**
-        * Given a DB type, construct the name of the appropriate child class of
-        * DatabaseBase. This is designed to replace all of the manual stuff like:
-        *    $class = 'Database' . ucfirst( strtolower( $dbType ) );
-        * as well as validate against the canonical list of DB types we have
-        *
-        * This factory function is mostly useful for when you need to connect to a
-        * database other than the MediaWiki default (such as for external auth,
-        * an extension, et cetera). Do not use this to connect to the MediaWiki
-        * database. Example uses in core:
-        * @see LoadBalancer::reallyOpenConnection()
-        * @see ForeignDBRepo::getMasterDB()
-        * @see WebInstallerDBConnect::execute()
-        *
-        * @since 1.18
-        *
-        * @param string $dbType A possible DB type
-        * @param array $p An array of options to pass to the constructor.
-        *    Valid options are: host, user, password, dbname, flags, tablePrefix, schema, driver
-        * @throws MWException If the database driver or extension cannot be found
-        * @return DatabaseBase|null DatabaseBase subclass or null
-        */
-       final public static function factory( $dbType, $p = [] ) {
-               $canonicalDBTypes = [
-                       'mysql' => [ 'mysqli', 'mysql' ],
-                       'postgres' => [],
-                       'sqlite' => [],
-                       'oracle' => [],
-                       'mssql' => [],
-               ];
-
-               $driver = false;
-               $dbType = strtolower( $dbType );
-               if ( isset( $canonicalDBTypes[$dbType] ) && $canonicalDBTypes[$dbType] ) {
-                       $possibleDrivers = $canonicalDBTypes[$dbType];
-                       if ( !empty( $p['driver'] ) ) {
-                               if ( in_array( $p['driver'], $possibleDrivers ) ) {
-                                       $driver = $p['driver'];
-                               } else {
-                                       throw new MWException( __METHOD__ .
-                                               " cannot construct Database with type '$dbType' and driver '{$p['driver']}'" );
-                               }
-                       } else {
-                               foreach ( $possibleDrivers as $posDriver ) {
-                                       if ( extension_loaded( $posDriver ) ) {
-                                               $driver = $posDriver;
-                                               break;
-                                       }
-                               }
-                       }
-               } else {
-                       $driver = $dbType;
-               }
-               if ( $driver === false ) {
-                       throw new MWException( __METHOD__ .
-                               " no viable database extension found for type '$dbType'" );
-               }
-
-               // Determine schema defaults. Currently Microsoft SQL Server uses $wgDBmwschema,
-               // and everything else doesn't use a schema (e.g. null)
-               // Although postgres and oracle support schemas, we don't use them (yet)
-               // to maintain backwards compatibility
-               $defaultSchemas = [
-                       'mssql' => 'get from global',
-               ];
+       public function getFlag( $flag ) {
+               return !!( $this->mFlags & $flag );
+       }
 
-               $class = 'Database' . ucfirst( $driver );
-               if ( class_exists( $class ) && is_subclass_of( $class, 'DatabaseBase' ) ) {
-                       // Resolve some defaults for b/c
-                       $p['host'] = isset( $p['host'] ) ? $p['host'] : false;
-                       $p['user'] = isset( $p['user'] ) ? $p['user'] : false;
-                       $p['password'] = isset( $p['password'] ) ? $p['password'] : false;
-                       $p['dbname'] = isset( $p['dbname'] ) ? $p['dbname'] : false;
-                       $p['flags'] = isset( $p['flags'] ) ? $p['flags'] : 0;
-                       $p['variables'] = isset( $p['variables'] ) ? $p['variables'] : [];
-                       $p['tablePrefix'] = isset( $p['tablePrefix'] ) ? $p['tablePrefix'] : 'get from global';
-                       if ( !isset( $p['schema'] ) ) {
-                               $p['schema'] = isset( $defaultSchemas[$dbType] ) ? $defaultSchemas[$dbType] : null;
-                       }
-                       $p['foreign'] = isset( $p['foreign'] ) ? $p['foreign'] : false;
+       public function getProperty( $name ) {
+               return $this->$name;
+       }
 
-                       return new $class( $p );
+       public function getWikiID() {
+               if ( $this->mTablePrefix ) {
+                       return "{$this->mDBname}-{$this->mTablePrefix}";
                } else {
-                       return null;
+                       return $this->mDBname;
                }
        }
 
+       /**
+        * Get information about an index into an object
+        * @param string $table Table name
+        * @param string $index Index name
+        * @param string $fname Calling function name
+        * @return mixed Database-specific index description class or false if the index does not exist
+        */
+       abstract function indexInfo( $table, $index, $fname = __METHOD__ );
+
+       /**
+        * Wrapper for addslashes()
+        *
+        * @param string $s String to be slashed.
+        * @return string Slashed string.
+        */
+       abstract function strencode( $s );
+
+       /**
+        * Called by serialize. Throw an exception when DB connection is serialized.
+        * This causes problems on some database engines because the connection is
+        * not restored on unserialize.
+        */
+       public function __sleep() {
+               throw new RuntimeException( 'Database serialization may cause problems, since ' .
+                       'the connection is not restored on wakeup.' );
+       }
+
        protected function installErrorHandler() {
                $this->mPHPError = false;
                $this->htmlErrors = ini_set( 'html_errors', '0' );
-               set_error_handler( [ $this, 'connectionErrorHandler' ] );
+               set_error_handler( [ $this, 'connectionerrorLogger' ] );
        }
 
        /**
@@ -670,12 +720,12 @@ abstract class DatabaseBase implements IDatabase {
         * @param int $errno
         * @param string $errstr
         */
-       public function connectionErrorHandler( $errno, $errstr ) {
+       public function connectionerrorLogger( $errno, $errstr ) {
                $this->mPHPError = $errstr;
        }
 
        /**
-        * Create a log context to pass to wfLogDBError or other logging functions.
+        * Create a log context to pass to PSR logging functions.
         *
         * @param array $extras Additional data to add to context
         * @return array
@@ -692,21 +742,15 @@ abstract class DatabaseBase implements IDatabase {
        }
 
        public function close() {
-               if ( count( $this->mTrxIdleCallbacks ) ) { // sanity
-                       throw new MWException( "Transaction idle callbacks still pending." );
-               }
                if ( $this->mConn ) {
                        if ( $this->trxLevel() ) {
-                               if ( !$this->mTrxAutomatic ) {
-                                       wfWarn( "Transaction still in progress (from {$this->mTrxFname}), " .
-                                               " performing implicit commit before closing connection!" );
-                               }
-
-                               $this->commit( __METHOD__, 'flush' );
+                               $this->commit( __METHOD__, self::FLUSHING_INTERNAL );
                        }
 
                        $closed = $this->closeConnection();
                        $this->mConn = false;
+               } elseif ( $this->mTrxIdleCallbacks || $this->mTrxEndCallbacks ) { // sanity
+                       throw new RuntimeException( "Transaction callbacks still pending." );
                } else {
                        $closed = true;
                }
@@ -760,7 +804,16 @@ abstract class DatabaseBase implements IDatabase {
         * @return bool
         */
        protected function isWriteQuery( $sql ) {
-               return !preg_match( '/^(?:SELECT|BEGIN|ROLLBACK|COMMIT|SET|SHOW|EXPLAIN|\(SELECT)\b/i', $sql );
+               return !preg_match(
+                       '/^(?:SELECT|BEGIN|ROLLBACK|COMMIT|SET|SHOW|EXPLAIN|\(SELECT)\b/i', $sql );
+       }
+
+       /**
+        * @param $sql
+        * @return string|null
+        */
+       protected function getQueryVerb( $sql ) {
+               return preg_match( '/^\s*([a-z]+)/i', $sql, $m ) ? strtoupper( $m[1] ) : null;
        }
 
        /**
@@ -773,17 +826,18 @@ abstract class DatabaseBase implements IDatabase {
         * @return bool
         */
        protected function isTransactableQuery( $sql ) {
-               $verb = substr( $sql, 0, strcspn( $sql, " \t\r\n" ) );
-               return !in_array( $verb, [ 'BEGIN', 'COMMIT', 'ROLLBACK', 'SHOW', 'SET' ] );
+               $verb = $this->getQueryVerb( $sql );
+               return !in_array( $verb, [ 'BEGIN', 'COMMIT', 'ROLLBACK', 'SHOW', 'SET' ], true );
        }
 
        public function query( $sql, $fname = __METHOD__, $tempIgnore = false ) {
                global $wgUser;
 
+               $priorWritesPending = $this->writesOrCallbacksPending();
                $this->mLastQuery = $sql;
 
-               $isWriteQuery = $this->isWriteQuery( $sql );
-               if ( $isWriteQuery ) {
+               $isWrite = $this->isWriteQuery( $sql );
+               if ( $isWrite ) {
                        $reason = $this->getReadOnlyReason();
                        if ( $reason !== false ) {
                                throw new DBReadOnlyError( $this, "Database is read-only: $reason" );
@@ -807,120 +861,193 @@ abstract class DatabaseBase implements IDatabase {
                // Or, for one-word queries (like "BEGIN" or COMMIT") add it to the end (bug 42598)
                $commentedSql = preg_replace( '/\s|$/', " /* $fname $userName */ ", $sql, 1 );
 
-               if ( !$this->mTrxLevel && $this->getFlag( DBO_TRX ) && $this->isTransactableQuery( $sql ) ) {
-                       $this->begin( __METHOD__ . " ($fname)" );
+               # Start implicit transactions that wrap the request if DBO_TRX is enabled
+               if ( !$this->mTrxLevel && $this->getFlag( DBO_TRX )
+                       && $this->isTransactableQuery( $sql )
+               ) {
+                       $this->begin( __METHOD__ . " ($fname)", self::TRANSACTION_INTERNAL );
                        $this->mTrxAutomatic = true;
                }
 
                # Keep track of whether the transaction has write queries pending
-               if ( $this->mTrxLevel && !$this->mTrxDoneWrites && $isWriteQuery ) {
+               if ( $this->mTrxLevel && !$this->mTrxDoneWrites && $isWrite ) {
                        $this->mTrxDoneWrites = true;
-                       $this->getTransactionProfiler()->transactionWritingIn(
+                       $this->trxProfiler->transactionWritingIn(
                                $this->mServer, $this->mDBname, $this->mTrxShortId );
                }
 
-               $isMaster = !is_null( $this->getLBInfo( 'master' ) );
-               # generalizeSQL will probably cut down the query to reasonable
-               # logging size most of the time. The substr is really just a sanity check.
-               if ( $isMaster ) {
-                       $queryProf = 'query-m: ' . substr( DatabaseBase::generalizeSQL( $sql ), 0, 255 );
-                       $totalProf = 'DatabaseBase::query-master';
-               } else {
-                       $queryProf = 'query: ' . substr( DatabaseBase::generalizeSQL( $sql ), 0, 255 );
-                       $totalProf = 'DatabaseBase::query';
-               }
-               # Include query transaction state
-               $queryProf .= $this->mTrxShortId ? " [TRX#{$this->mTrxShortId}]" : "";
-
-               $profiler = Profiler::instance();
-               if ( !$profiler instanceof ProfilerStub ) {
-                       $totalProfSection = $profiler->scopedProfileIn( $totalProf );
-                       $queryProfSection = $profiler->scopedProfileIn( $queryProf );
-               }
-
                if ( $this->debug() ) {
-                       wfDebugLog( 'queries', sprintf( "%s: %s", $this->mDBname, $commentedSql ) );
+                       $this->queryLogger->debug( "{$this->mDBname} {$commentedSql}" );
                }
 
-               $queryId = MWDebug::query( $sql, $fname, $isMaster );
-
                # Avoid fatals if close() was called
                $this->assertOpen();
 
-               # Do the query and handle errors
-               $startTime = microtime( true );
-               $ret = $this->doQuery( $commentedSql );
-               $queryRuntime = microtime( true ) - $startTime;
-               # Log the query time and feed it into the DB trx profiler
-               $this->getTransactionProfiler()->recordQueryCompletion(
-                       $queryProf, $startTime, $isWriteQuery, $this->affectedRows() );
-
-               MWDebug::queryTime( $queryId );
+               # Send the query to the server
+               $ret = $this->doProfiledQuery( $sql, $commentedSql, $isWrite, $fname );
 
                # Try reconnecting if the connection was lost
                if ( false === $ret && $this->wasErrorReissuable() ) {
-                       # Transaction is gone; this can mean lost writes or REPEATABLE-READ snapshots
-                       $hadTrx = $this->mTrxLevel;
-                       # T127428: for non-write transactions, a disconnect and a COMMIT are similar:
-                       # neither changed data and in both cases any read snapshots are reset anyway.
-                       $isNoopCommit = ( !$this->writesOrCallbacksPending() && $sql === 'COMMIT' );
-                       # Update state tracking to reflect transaction loss
-                       $this->mTrxLevel = 0;
-                       $this->mTrxIdleCallbacks = []; // bug 65263
-                       $this->mTrxPreCommitCallbacks = []; // bug 65263
-                       wfDebug( "Connection lost, reconnecting...\n" );
-                       # Stash the last error values since ping() might clear them
+                       $recoverable = $this->canRecoverFromDisconnect( $sql, $priorWritesPending );
+                       # Stash the last error values before anything might clear them
                        $lastError = $this->lastError();
                        $lastErrno = $this->lastErrno();
-                       if ( $this->ping() ) {
-                               wfDebug( "Reconnected\n" );
-                               $server = $this->getServer();
-                               $msg = __METHOD__ . ": lost connection to $server; reconnected";
-                               wfDebugLog( 'DBPerformance', "$msg:\n" . wfBacktrace( true ) );
-
-                               if ( ( $hadTrx && !$isNoopCommit ) || $this->mNamedLocksHeld ) {
-                                       # Leave $ret as false and let an error be reported.
-                                       # Callers may catch the exception and continue to use the DB.
-                                       $this->reportQueryError( $lastError, $lastErrno, $sql, $fname, $tempIgnore );
+                       # Update state tracking to reflect transaction loss due to disconnection
+                       $this->handleTransactionLoss();
+                       if ( $this->reconnect() ) {
+                               $msg = __METHOD__ . ": lost connection to {$this->getServer()}; reconnected";
+                               $this->connLogger->warning( $msg );
+                               $this->queryLogger->warning(
+                                       "$msg:\n" . ( new RuntimeException() )->getTraceAsString() );
+
+                               if ( !$recoverable ) {
+                                       # Callers may catch the exception and continue to use the DB
+                                       $this->reportQueryError( $lastError, $lastErrno, $sql, $fname );
                                } else {
-                                       # Should be safe to silently retry (no trx/callbacks/locks)
-                                       $startTime = microtime( true );
-                                       $ret = $this->doQuery( $commentedSql );
-                                       $queryRuntime = microtime( true ) - $startTime;
-                                       # Log the query time and feed it into the DB trx profiler
-                                       $this->getTransactionProfiler()->recordQueryCompletion(
-                                               $queryProf, $startTime, $isWriteQuery, $this->affectedRows() );
+                                       # Should be safe to silently retry the query
+                                       $ret = $this->doProfiledQuery( $sql, $commentedSql, $isWrite, $fname );
                                }
                        } else {
-                               wfDebug( "Failed\n" );
+                               $msg = __METHOD__ . ": lost connection to {$this->getServer()} permanently";
+                               $this->connLogger->error( $msg );
                        }
                }
 
                if ( false === $ret ) {
+                       # Deadlocks cause the entire transaction to abort, not just the statement.
+                       # http://dev.mysql.com/doc/refman/5.7/en/innodb-error-handling.html
+                       # https://www.postgresql.org/docs/9.1/static/explicit-locking.html
+                       if ( $this->wasDeadlock() ) {
+                               if ( $this->explicitTrxActive() || $priorWritesPending ) {
+                                       $tempIgnore = false; // not recoverable
+                               }
+                               # Update state tracking to reflect transaction loss
+                               $this->handleTransactionLoss();
+                       }
+
                        $this->reportQueryError(
                                $this->lastError(), $this->lastErrno(), $sql, $fname, $tempIgnore );
                }
 
                $res = $this->resultObject( $ret );
 
-               // Destroy profile sections in the opposite order to their creation
-               ScopedCallback::consume( $queryProfSection );
-               ScopedCallback::consume( $totalProfSection );
+               return $res;
+       }
 
-               if ( $isWriteQuery && $this->mTrxLevel ) {
-                       $this->mTrxWriteDuration += $queryRuntime;
-                       $this->mTrxWriteCallers[] = $fname;
+       private function doProfiledQuery( $sql, $commentedSql, $isWrite, $fname ) {
+               $isMaster = !is_null( $this->getLBInfo( 'master' ) );
+               # generalizeSQL() will probably cut down the query to reasonable
+               # logging size most of the time. The substr is really just a sanity check.
+               if ( $isMaster ) {
+                       $queryProf = 'query-m: ' . substr( self::generalizeSQL( $sql ), 0, 255 );
+               } else {
+                       $queryProf = 'query: ' . substr( self::generalizeSQL( $sql ), 0, 255 );
                }
 
-               return $res;
+               # Include query transaction state
+               $queryProf .= $this->mTrxShortId ? " [TRX#{$this->mTrxShortId}]" : "";
+
+               $startTime = microtime( true );
+               $this->profiler->profileIn( $queryProf );
+               $ret = $this->doQuery( $commentedSql );
+               $this->profiler->profileOut( $queryProf );
+               $queryRuntime = max( microtime( true ) - $startTime, 0.0 );
+
+               unset( $queryProfSection ); // profile out (if set)
+
+               if ( $ret !== false ) {
+                       $this->lastPing = $startTime;
+                       if ( $isWrite && $this->mTrxLevel ) {
+                               $this->updateTrxWriteQueryTime( $sql, $queryRuntime );
+                               $this->mTrxWriteCallers[] = $fname;
+                       }
+               }
+
+               if ( $sql === self::PING_QUERY ) {
+                       $this->mRTTEstimate = $queryRuntime;
+               }
+
+               $this->trxProfiler->recordQueryCompletion(
+                       $queryProf, $startTime, $isWrite, $this->affectedRows()
+               );
+               MWDebug::query( $sql, $fname, $isMaster, $queryRuntime );
+
+               return $ret;
+       }
+
+       /**
+        * Update the estimated run-time of a query, not counting large row lock times
+        *
+        * LoadBalancer can be set to rollback transactions that will create huge replication
+        * lag. It bases this estimate off of pendingWriteQueryDuration(). Certain simple
+        * queries, like inserting a row can take a long time due to row locking. This method
+        * uses some simple heuristics to discount those cases.
+        *
+        * @param string $sql A SQL write query
+        * @param float $runtime Total runtime, including RTT
+        */
+       private function updateTrxWriteQueryTime( $sql, $runtime ) {
+               // Whether this is indicative of replica DB runtime (except for RBR or ws_repl)
+               $indicativeOfReplicaRuntime = true;
+               if ( $runtime > self::SLOW_WRITE_SEC ) {
+                       $verb = $this->getQueryVerb( $sql );
+                       // insert(), upsert(), replace() are fast unless bulky in size or blocked on locks
+                       if ( $verb === 'INSERT' ) {
+                               $indicativeOfReplicaRuntime = $this->affectedRows() > self::SMALL_WRITE_ROWS;
+                       } elseif ( $verb === 'REPLACE' ) {
+                               $indicativeOfReplicaRuntime = $this->affectedRows() > self::SMALL_WRITE_ROWS / 2;
+                       }
+               }
+
+               $this->mTrxWriteDuration += $runtime;
+               $this->mTrxWriteQueryCount += 1;
+               if ( $indicativeOfReplicaRuntime ) {
+                       $this->mTrxWriteAdjDuration += $runtime;
+                       $this->mTrxWriteAdjQueryCount += 1;
+               }
+       }
+
+       private function canRecoverFromDisconnect( $sql, $priorWritesPending ) {
+               # Transaction dropped; this can mean lost writes, or REPEATABLE-READ snapshots.
+               # Dropped connections also mean that named locks are automatically released.
+               # Only allow error suppression in autocommit mode or when the lost transaction
+               # didn't matter anyway (aside from DBO_TRX snapshot loss).
+               if ( $this->mNamedLocksHeld ) {
+                       return false; // possible critical section violation
+               } elseif ( $sql === 'COMMIT' ) {
+                       return !$priorWritesPending; // nothing written anyway? (T127428)
+               } elseif ( $sql === 'ROLLBACK' ) {
+                       return true; // transaction lost...which is also what was requested :)
+               } elseif ( $this->explicitTrxActive() ) {
+                       return false; // don't drop atomocity
+               } elseif ( $priorWritesPending ) {
+                       return false; // prior writes lost from implicit transaction
+               }
+
+               return true;
+       }
+
+       private function handleTransactionLoss() {
+               $this->mTrxLevel = 0;
+               $this->mTrxIdleCallbacks = []; // bug 65263
+               $this->mTrxPreCommitCallbacks = []; // bug 65263
+               try {
+                       // Handle callbacks in mTrxEndCallbacks
+                       $this->runOnTransactionIdleCallbacks( self::TRIGGER_ROLLBACK );
+                       $this->runTransactionListenerCallbacks( self::TRIGGER_ROLLBACK );
+                       return null;
+               } catch ( Exception $e ) {
+                       // Already logged; move on...
+                       return $e;
+               }
        }
 
        public function reportQueryError( $error, $errno, $sql, $fname, $tempIgnore = false ) {
                if ( $this->ignoreErrors() || $tempIgnore ) {
-                       wfDebug( "SQL ERROR (ignored): $error\n" );
+                       $this->queryLogger->debug( "SQL ERROR (ignored): $error\n" );
                } else {
                        $sql1line = mb_substr( str_replace( "\n", "\\n", $sql ), 0, 5 * 1024 );
-                       wfLogDBError(
+                       $this->queryLogger->error(
                                "{fname}\t{db_server}\t{errno}\t{error}\t{sql1line}",
                                $this->getLogContext( [
                                        'method' => __METHOD__,
@@ -930,7 +1057,7 @@ abstract class DatabaseBase implements IDatabase {
                                        'fname' => $fname,
                                ] )
                        );
-                       wfDebug( "SQL ERROR: " . $error . "\n" );
+                       $this->queryLogger->debug( "SQL ERROR: " . $error . "\n" );
                        throw new DBQueryError( $this, $error, $errno, $sql, $fname );
                }
        }
@@ -949,7 +1076,7 @@ abstract class DatabaseBase implements IDatabase {
         *
         * @return array
         */
-       protected function prepare( $sql, $func = 'DatabaseBase::prepare' ) {
+       protected function prepare( $sql, $func = __METHOD__ ) {
                /* MySQL doesn't support prepared statements (yet), so just
                 * pack up the query for reference. We'll manually replace
                 * the bits later.
@@ -1522,7 +1649,7 @@ abstract class DatabaseBase implements IDatabase {
 
        public function makeList( $a, $mode = LIST_COMMA ) {
                if ( !is_array( $a ) ) {
-                       throw new DBUnexpectedError( $this, 'DatabaseBase::makeList called with incorrect parameters' );
+                       throw new DBUnexpectedError( $this, __METHOD__ . ' called with incorrect parameters' );
                }
 
                $first = true;
@@ -1553,7 +1680,7 @@ abstract class DatabaseBase implements IDatabase {
                                        unset( $value[$nullKey] );
                                }
                                if ( count( $value ) == 0 && !$includeNull ) {
-                                       throw new MWException( __METHOD__ . ": empty input for field $field" );
+                                       throw new InvalidArgumentException( __METHOD__ . ": empty input for field $field" );
                                } elseif ( count( $value ) == 0 ) {
                                        // only check if $field is null
                                        $list .= "$field IS NULL";
@@ -1650,6 +1777,15 @@ abstract class DatabaseBase implements IDatabase {
                return '(' . $this->selectSQLText( $table, $fld, $conds, null, [], $join_conds ) . ')';
        }
 
+       /**
+        * @param string $field Field or column to cast
+        * @return string
+        * @since 1.28
+        */
+       public function buildStringCast( $field ) {
+               return $field;
+       }
+
        public function selectDB( $db ) {
                # Stub. Shouldn't cause serious problems if it's not overridden, but
                # if your database engine supports a concept similar to MySQL's
@@ -1687,7 +1823,6 @@ abstract class DatabaseBase implements IDatabase {
         * @return string Full database name
         */
        public function tableName( $name, $format = 'quoted' ) {
-               global $wgSharedDB, $wgSharedPrefix, $wgSharedTables, $wgSharedSchema;
                # Skip the entire process when we have a string quoted on both ends.
                # Note that we check the end so that we will still quote any use of
                # use of `database`.table. But won't break things if someone wants
@@ -1724,14 +1859,14 @@ abstract class DatabaseBase implements IDatabase {
                        $schema = null;
                } else {
                        list( $table ) = $dbDetails;
-                       if ( $wgSharedDB !== null # We have a shared database
-                               && $this->mForeign == false # We're not working on a foreign database
-                               && !$this->isQuotedIdentifier( $table ) # Prevent shared tables listing '`table`'
-                               && in_array( $table, $wgSharedTables ) # A shared table is selected
-                       ) {
-                               $database = $wgSharedDB;
-                               $schema = $wgSharedSchema === null ? $this->mSchema : $wgSharedSchema;
-                               $prefix = $wgSharedPrefix === null ? $this->mTablePrefix : $wgSharedPrefix;
+                       if ( isset( $this->tableAliases[$table] ) ) {
+                               $database = $this->tableAliases[$table]['dbname'];
+                               $schema = is_string( $this->tableAliases[$table]['schema'] )
+                                       ? $this->tableAliases[$table]['schema']
+                                       : $this->mSchema;
+                               $prefix = is_string( $this->tableAliases[$table]['prefix'] )
+                                       ? $this->tableAliases[$table]['prefix']
+                                       : $this->mTablePrefix;
                        } else {
                                $database = null;
                                $schema = $this->mSchema; # Default schema
@@ -1742,7 +1877,9 @@ abstract class DatabaseBase implements IDatabase {
                # Quote $table and apply the prefix if not quoted.
                # $tableName might be empty if this is called from Database::replaceVars()
                $tableName = "{$prefix}{$table}";
-               if ( $format == 'quoted' && !$this->isQuotedIdentifier( $tableName ) && $tableName !== '' ) {
+               if ( $format == 'quoted'
+                       && !$this->isQuotedIdentifier( $tableName ) && $tableName !== ''
+               ) {
                        $tableName = $this->addIdentifierQuotes( $tableName );
                }
 
@@ -1828,7 +1965,7 @@ abstract class DatabaseBase implements IDatabase {
        /**
         * Gets an array of aliased table names
         *
-        * @param array $tables Array( [alias] => table )
+        * @param array $tables [ [alias] => table ]
         * @return string[] See tableNameWithAlias()
         */
        public function tableNamesWithAlias( $tables ) {
@@ -1862,7 +1999,7 @@ abstract class DatabaseBase implements IDatabase {
        /**
         * Gets an array of aliased field names
         *
-        * @param array $fields Array( [alias] => field )
+        * @param array $fields [ [alias] => field ]
         * @return string[] See fieldNameWithAlias()
         */
        public function fieldNamesWithAlias( $fields ) {
@@ -2197,7 +2334,7 @@ abstract class DatabaseBase implements IDatabase {
 
                $useTrx = !$this->mTrxLevel;
                if ( $useTrx ) {
-                       $this->begin( $fname );
+                       $this->begin( $fname, self::TRANSACTION_INTERNAL );
                }
                try {
                        # Update any existing conflicting row(s)
@@ -2210,12 +2347,12 @@ abstract class DatabaseBase implements IDatabase {
                        $ok = $this->insert( $table, $rows, $fname, [ 'IGNORE' ] ) && $ok;
                } catch ( Exception $e ) {
                        if ( $useTrx ) {
-                               $this->rollback( $fname );
+                               $this->rollback( $fname, self::FLUSHING_INTERNAL );
                        }
                        throw $e;
                }
                if ( $useTrx ) {
-                       $this->commit( $fname );
+                       $this->commit( $fname, self::FLUSHING_INTERNAL );
                }
 
                return $ok;
@@ -2225,8 +2362,7 @@ abstract class DatabaseBase implements IDatabase {
                $fname = __METHOD__
        ) {
                if ( !$conds ) {
-                       throw new DBUnexpectedError( $this,
-                               'DatabaseBase::deleteJoin() called with empty $conds' );
+                       throw new DBUnexpectedError( $this, __METHOD__ . ' called with empty $conds' );
                }
 
                $delTable = $this->tableName( $delTable );
@@ -2250,7 +2386,7 @@ abstract class DatabaseBase implements IDatabase {
        public function textFieldSize( $table, $field ) {
                $table = $this->tableName( $table );
                $sql = "SHOW COLUMNS FROM $table LIKE \"$field\";";
-               $res = $this->query( $sql, 'DatabaseBase::textFieldSize' );
+               $res = $this->query( $sql, __METHOD__ );
                $row = $this->fetchObject( $res );
 
                $m = [];
@@ -2278,7 +2414,7 @@ abstract class DatabaseBase implements IDatabase {
 
        public function delete( $table, $conds, $fname = __METHOD__ ) {
                if ( !$conds ) {
-                       throw new DBUnexpectedError( $this, 'DatabaseBase::delete() called with no conditions' );
+                       throw new DBUnexpectedError( $this, __METHOD__ . ' called with no conditions' );
                }
 
                $table = $this->tableName( $table );
@@ -2294,7 +2430,46 @@ abstract class DatabaseBase implements IDatabase {
                return $this->query( $sql, $fname );
        }
 
-       public function insertSelect( $destTable, $srcTable, $varMap, $conds,
+       public function insertSelect(
+               $destTable, $srcTable, $varMap, $conds,
+               $fname = __METHOD__, $insertOptions = [], $selectOptions = []
+       ) {
+               if ( $this->cliMode ) {
+                       // For massive migrations with downtime, we don't want to select everything
+                       // into memory and OOM, so do all this native on the server side if possible.
+                       return $this->nativeInsertSelect(
+                               $destTable,
+                               $srcTable,
+                               $varMap,
+                               $conds,
+                               $fname,
+                               $insertOptions,
+                               $selectOptions
+                       );
+               }
+
+               // For web requests, do a locking SELECT and then INSERT. This puts the SELECT burden
+               // on only the master (without needing row-based-replication). It also makes it easy to
+               // know how big the INSERT is going to be.
+               $fields = [];
+               foreach ( $varMap as $dstColumn => $sourceColumnOrSql ) {
+                       $fields[] = $this->fieldNameWithAlias( $sourceColumnOrSql, $dstColumn );
+               }
+               $selectOptions[] = 'FOR UPDATE';
+               $res = $this->select( $srcTable, implode( ',', $fields ), $conds, $fname, $selectOptions );
+               if ( !$res ) {
+                       return false;
+               }
+
+               $rows = [];
+               foreach ( $res as $row ) {
+                       $rows[] = (array)$row;
+               }
+
+               return $this->insert( $destTable, $rows, $fname, $insertOptions );
+       }
+
+       public function nativeInsertSelect( $destTable, $srcTable, $varMap, $conds,
                $fname = __METHOD__,
                $insertOptions = [], $selectOptions = []
        ) {
@@ -2424,14 +2599,19 @@ abstract class DatabaseBase implements IDatabase {
         * queries. If a deadlock occurs during the processing, the transaction
         * will be rolled back and the callback function will be called again.
         *
+        * Avoid using this method outside of Job or Maintenance classes.
+        *
         * Usage:
         *   $dbw->deadlockLoop( callback, ... );
         *
         * Extra arguments are passed through to the specified callback function.
+        * This method requires that no transactions are already active to avoid
+        * causing premature commits or exceptions.
         *
         * Returns whatever the callback function returned on its successful,
         * iteration, or false on error, for example if the retry limit was
         * reached.
+        *
         * @return mixed
         * @throws DBUnexpectedError
         * @throws Exception
@@ -2487,94 +2667,174 @@ abstract class DatabaseBase implements IDatabase {
                return false;
        }
 
-       final public function onTransactionIdle( $callback ) {
-               $this->mTrxIdleCallbacks[] = [ $callback, wfGetCaller() ];
+       public function serverIsReadOnly() {
+               return false;
+       }
+
+       final public function onTransactionResolution( callable $callback, $fname = __METHOD__ ) {
+               if ( !$this->mTrxLevel ) {
+                       throw new DBUnexpectedError( $this, "No transaction is active." );
+               }
+               $this->mTrxEndCallbacks[] = [ $callback, $fname ];
+       }
+
+       final public function onTransactionIdle( callable $callback, $fname = __METHOD__ ) {
+               $this->mTrxIdleCallbacks[] = [ $callback, $fname ];
                if ( !$this->mTrxLevel ) {
-                       $this->runOnTransactionIdleCallbacks();
+                       $this->runOnTransactionIdleCallbacks( self::TRIGGER_IDLE );
                }
        }
 
-       final public function onTransactionPreCommitOrIdle( $callback ) {
+       final public function onTransactionPreCommitOrIdle( callable $callback, $fname = __METHOD__ ) {
                if ( $this->mTrxLevel ) {
-                       $this->mTrxPreCommitCallbacks[] = [ $callback, wfGetCaller() ];
+                       $this->mTrxPreCommitCallbacks[] = [ $callback, $fname ];
+               } else {
+                       // If no transaction is active, then make one for this callback
+                       $this->startAtomic( __METHOD__ );
+                       try {
+                               call_user_func( $callback );
+                               $this->endAtomic( __METHOD__ );
+                       } catch ( Exception $e ) {
+                               $this->rollback( __METHOD__, self::FLUSHING_INTERNAL );
+                               throw $e;
+                       }
+               }
+       }
+
+       final public function setTransactionListener( $name, callable $callback = null ) {
+               if ( $callback ) {
+                       $this->mTrxRecurringCallbacks[$name] = $callback;
                } else {
-                       $this->onTransactionIdle( $callback ); // this will trigger immediately
+                       unset( $this->mTrxRecurringCallbacks[$name] );
                }
        }
 
        /**
-        * Actually any "on transaction idle" callbacks.
+        * Whether to disable running of post-COMMIT/ROLLBACK callbacks
+        *
+        * This method should not be used outside of Database/LoadBalancer
+        *
+        * @param bool $suppress
+        * @since 1.28
+        */
+       final public function setTrxEndCallbackSuppression( $suppress ) {
+               $this->mTrxEndCallbacksSuppressed = $suppress;
+       }
+
+       /**
+        * Actually run and consume any "on transaction idle/resolution" callbacks.
+        *
+        * This method should not be used outside of Database/LoadBalancer
         *
+        * @param integer $trigger IDatabase::TRIGGER_* constant
         * @since 1.20
+        * @throws Exception
         */
-       protected function runOnTransactionIdleCallbacks() {
-               $autoTrx = $this->getFlag( DBO_TRX ); // automatic begin() enabled?
+       public function runOnTransactionIdleCallbacks( $trigger ) {
+               if ( $this->mTrxEndCallbacksSuppressed ) {
+                       return;
+               }
 
-               $e = $ePrior = null; // last exception
+               $autoTrx = $this->getFlag( DBO_TRX ); // automatic begin() enabled?
+               /** @var Exception $e */
+               $e = null; // first exception
                do { // callbacks may add callbacks :)
-                       $callbacks = $this->mTrxIdleCallbacks;
-                       $this->mTrxIdleCallbacks = []; // recursion guard
+                       $callbacks = array_merge(
+                               $this->mTrxIdleCallbacks,
+                               $this->mTrxEndCallbacks // include "transaction resolution" callbacks
+                       );
+                       $this->mTrxIdleCallbacks = []; // consumed (and recursion guard)
+                       $this->mTrxEndCallbacks = []; // consumed (recursion guard)
                        foreach ( $callbacks as $callback ) {
                                try {
                                        list( $phpCallback ) = $callback;
                                        $this->clearFlag( DBO_TRX ); // make each query its own transaction
-                                       call_user_func( $phpCallback );
+                                       call_user_func_array( $phpCallback, [ $trigger ] );
                                        if ( $autoTrx ) {
                                                $this->setFlag( DBO_TRX ); // restore automatic begin()
                                        } else {
                                                $this->clearFlag( DBO_TRX ); // restore auto-commit
                                        }
-                               } catch ( Exception $e ) {
-                                       if ( $ePrior ) {
-                                               MWExceptionHandler::logException( $ePrior );
-                                       }
-                                       $ePrior = $e;
+                               } catch ( Exception $ex ) {
+                                       call_user_func( $this->errorLogger, $ex );
+                                       $e = $e ?: $ex;
                                        // Some callbacks may use startAtomic/endAtomic, so make sure
                                        // their transactions are ended so other callbacks don't fail
                                        if ( $this->trxLevel() ) {
-                                               $this->rollback( __METHOD__ );
+                                               $this->rollback( __METHOD__, self::FLUSHING_INTERNAL );
                                        }
                                }
                        }
                } while ( count( $this->mTrxIdleCallbacks ) );
 
                if ( $e instanceof Exception ) {
-                       throw $e; // re-throw any last exception
+                       throw $e; // re-throw any first exception
                }
        }
 
        /**
-        * Actually any "on transaction pre-commit" callbacks.
+        * Actually run and consume any "on transaction pre-commit" callbacks.
+        *
+        * This method should not be used outside of Database/LoadBalancer
         *
         * @since 1.22
+        * @throws Exception
         */
-       protected function runOnTransactionPreCommitCallbacks() {
-               $e = $ePrior = null; // last exception
+       public function runOnTransactionPreCommitCallbacks() {
+               $e = null; // first exception
                do { // callbacks may add callbacks :)
                        $callbacks = $this->mTrxPreCommitCallbacks;
-                       $this->mTrxPreCommitCallbacks = []; // recursion guard
+                       $this->mTrxPreCommitCallbacks = []; // consumed (and recursion guard)
                        foreach ( $callbacks as $callback ) {
                                try {
                                        list( $phpCallback ) = $callback;
                                        call_user_func( $phpCallback );
-                               } catch ( Exception $e ) {
-                                       if ( $ePrior ) {
-                                               MWExceptionHandler::logException( $ePrior );
-                                       }
-                                       $ePrior = $e;
+                               } catch ( Exception $ex ) {
+                                       call_user_func( $this->errorLogger, $ex );
+                                       $e = $e ?: $ex;
                                }
                        }
                } while ( count( $this->mTrxPreCommitCallbacks ) );
 
                if ( $e instanceof Exception ) {
-                       throw $e; // re-throw any last exception
+                       throw $e; // re-throw any first exception
+               }
+       }
+
+       /**
+        * Actually run any "transaction listener" callbacks.
+        *
+        * This method should not be used outside of Database/LoadBalancer
+        *
+        * @param integer $trigger IDatabase::TRIGGER_* constant
+        * @throws Exception
+        * @since 1.20
+        */
+       public function runTransactionListenerCallbacks( $trigger ) {
+               if ( $this->mTrxEndCallbacksSuppressed ) {
+                       return;
+               }
+
+               /** @var Exception $e */
+               $e = null; // first exception
+
+               foreach ( $this->mTrxRecurringCallbacks as $phpCallback ) {
+                       try {
+                               $phpCallback( $trigger, $this );
+                       } catch ( Exception $ex ) {
+                               call_user_func( $this->errorLogger, $ex );
+                               $e = $e ?: $ex;
+                       }
+               }
+
+               if ( $e instanceof Exception ) {
+                       throw $e; // re-throw any first exception
                }
        }
 
        final public function startAtomic( $fname = __METHOD__ ) {
                if ( !$this->mTrxLevel ) {
-                       $this->begin( $fname );
-                       $this->mTrxAutomatic = true;
+                       $this->begin( $fname, self::TRANSACTION_INTERNAL );
                        // If DBO_TRX is set, a series of startAtomic/endAtomic pairs will result
                        // in all changes being in one transaction to keep requests transactional.
                        if ( !$this->getFlag( DBO_TRX ) ) {
@@ -2587,88 +2847,76 @@ abstract class DatabaseBase implements IDatabase {
 
        final public function endAtomic( $fname = __METHOD__ ) {
                if ( !$this->mTrxLevel ) {
-                       throw new DBUnexpectedError( $this, 'No atomic transaction is open.' );
+                       throw new DBUnexpectedError( $this, "No atomic transaction is open (got $fname)." );
                }
                if ( !$this->mTrxAtomicLevels ||
                        array_pop( $this->mTrxAtomicLevels ) !== $fname
                ) {
-                       throw new DBUnexpectedError( $this, 'Invalid atomic section ended.' );
+                       throw new DBUnexpectedError( $this, "Invalid atomic section ended (got $fname)." );
                }
 
                if ( !$this->mTrxAtomicLevels && $this->mTrxAutomaticAtomic ) {
-                       $this->commit( $fname, 'flush' );
+                       $this->commit( $fname, self::FLUSHING_INTERNAL );
                }
        }
 
        final public function doAtomicSection( $fname, callable $callback ) {
                $this->startAtomic( $fname );
                try {
-                       call_user_func_array( $callback, [ $this, $fname ] );
+                       $res = call_user_func_array( $callback, [ $this, $fname ] );
                } catch ( Exception $e ) {
-                       $this->rollback( $fname );
+                       $this->rollback( $fname, self::FLUSHING_INTERNAL );
                        throw $e;
                }
                $this->endAtomic( $fname );
+
+               return $res;
        }
 
-       final public function begin( $fname = __METHOD__ ) {
-               if ( $this->mTrxLevel ) { // implicit commit
+       final public function begin( $fname = __METHOD__, $mode = self::TRANSACTION_EXPLICIT ) {
+               // Protect against mismatched atomic section, transaction nesting, and snapshot loss
+               if ( $this->mTrxLevel ) {
                        if ( $this->mTrxAtomicLevels ) {
-                               // If the current transaction was an automatic atomic one, then we definitely have
-                               // a problem. Same if there is any unclosed atomic level.
                                $levels = implode( ', ', $this->mTrxAtomicLevels );
-                               throw new DBUnexpectedError(
-                                       $this,
-                                       "Got explicit BEGIN from $fname while atomic section(s) $levels are open."
-                               );
+                               $msg = "$fname: Got explicit BEGIN while atomic section(s) $levels are open.";
+                               throw new DBUnexpectedError( $this, $msg );
                        } elseif ( !$this->mTrxAutomatic ) {
-                               // We want to warn about inadvertently nested begin/commit pairs, but not about
-                               // auto-committing implicit transactions that were started by query() via DBO_TRX
-                               throw new DBUnexpectedError(
-                                       $this,
-                                       "$fname: Transaction already in progress (from {$this->mTrxFname}), " .
-                                               " performing implicit commit!"
-                               );
+                               $msg = "$fname: Explicit transaction already active (from {$this->mTrxFname}).";
+                               throw new DBUnexpectedError( $this, $msg );
                        } else {
-                               // The transaction was automatic and has done write operations
-                               if ( $this->mTrxDoneWrites ) {
-                                       wfDebug( "$fname: Automatic transaction with writes in progress" .
-                                               " (from {$this->mTrxFname}), performing implicit commit!\n"
-                                       );
-                               }
-                       }
-
-                       $this->runOnTransactionPreCommitCallbacks();
-                       $writeTime = $this->pendingWriteQueryDuration();
-                       $this->doCommit( $fname );
-                       if ( $this->mTrxDoneWrites ) {
-                               $this->mDoneWrites = microtime( true );
-                               $this->getTransactionProfiler()->transactionWritingOut(
-                                       $this->mServer, $this->mDBname, $this->mTrxShortId, $writeTime );
+                               // @TODO: make this an exception at some point
+                               $msg = "$fname: Implicit transaction already active (from {$this->mTrxFname}).";
+                               $this->queryLogger->error( $msg );
+                               return; // join the main transaction set
                        }
-                       $this->runOnTransactionIdleCallbacks();
+               } elseif ( $this->getFlag( DBO_TRX ) && $mode !== self::TRANSACTION_INTERNAL ) {
+                       // @TODO: make this an exception at some point
+                       $msg = "$fname: Implicit transaction expected (DBO_TRX set).";
+                       $this->queryLogger->error( $msg );
+                       return; // let any writes be in the main transaction
                }
 
-               # Avoid fatals if close() was called
+               // Avoid fatals if close() was called
                $this->assertOpen();
 
                $this->doBegin( $fname );
                $this->mTrxTimestamp = microtime( true );
                $this->mTrxFname = $fname;
                $this->mTrxDoneWrites = false;
-               $this->mTrxAutomatic = false;
+               $this->mTrxAutomatic = ( $mode === self::TRANSACTION_INTERNAL );
                $this->mTrxAutomaticAtomic = false;
                $this->mTrxAtomicLevels = [];
-               $this->mTrxIdleCallbacks = [];
-               $this->mTrxPreCommitCallbacks = [];
-               $this->mTrxShortId = wfRandomString( 12 );
+               $this->mTrxShortId = sprintf( '%06x', mt_rand( 0, 0xffffff ) );
                $this->mTrxWriteDuration = 0.0;
+               $this->mTrxWriteQueryCount = 0;
+               $this->mTrxWriteAdjDuration = 0.0;
+               $this->mTrxWriteAdjQueryCount = 0;
                $this->mTrxWriteCallers = [];
                // First SELECT after BEGIN will establish the snapshot in REPEATABLE-READ.
-               // Get an estimate of the slave lag before then, treating estimate staleness
+               // Get an estimate of the replica DB lag before then, treating estimate staleness
                // as lag itself just to be safe
                $status = $this->getApproximateLagStatus();
-               $this->mTrxSlaveLag = $status['lag'] + ( microtime( true ) - $status['since'] );
+               $this->mTrxReplicaLag = $status['lag'] + ( microtime( true ) - $status['since'] );
        }
 
        /**
@@ -2688,40 +2936,45 @@ abstract class DatabaseBase implements IDatabase {
                        $levels = implode( ', ', $this->mTrxAtomicLevels );
                        throw new DBUnexpectedError(
                                $this,
-                               "Got COMMIT while atomic sections $levels are still open"
+                               "$fname: Got COMMIT while atomic sections $levels are still open."
                        );
                }
 
-               if ( $flush === 'flush' ) {
+               if ( $flush === self::FLUSHING_INTERNAL || $flush === self::FLUSHING_ALL_PEERS ) {
                        if ( !$this->mTrxLevel ) {
                                return; // nothing to do
                        } elseif ( !$this->mTrxAutomatic ) {
                                throw new DBUnexpectedError(
                                        $this,
-                                       "$fname: Flushing an explicit transaction, getting out of sync!"
+                                       "$fname: Flushing an explicit transaction, getting out of sync."
                                );
                        }
                } else {
                        if ( !$this->mTrxLevel ) {
-                               wfWarn( "$fname: No transaction to commit, something got out of sync!" );
+                               $this->queryLogger->error( "$fname: No transaction to commit, something got out of sync." );
                                return; // nothing to do
                        } elseif ( $this->mTrxAutomatic ) {
-                               wfWarn( "$fname: Explicit commit of implicit transaction. Something may be out of sync!" );
+                               // @TODO: make this an exception at some point
+                               $msg = "$fname: Explicit commit of implicit transaction.";
+                               $this->queryLogger->error( $msg );
+                               return; // wait for the main transaction set commit round
                        }
                }
 
-               # Avoid fatals if close() was called
+               // Avoid fatals if close() was called
                $this->assertOpen();
 
                $this->runOnTransactionPreCommitCallbacks();
-               $writeTime = $this->pendingWriteQueryDuration();
+               $writeTime = $this->pendingWriteQueryDuration( self::ESTIMATE_DB_APPLY );
                $this->doCommit( $fname );
                if ( $this->mTrxDoneWrites ) {
                        $this->mDoneWrites = microtime( true );
-                       $this->getTransactionProfiler()->transactionWritingOut(
+                       $this->trxProfiler->transactionWritingOut(
                                $this->mServer, $this->mDBname, $this->mTrxShortId, $writeTime );
                }
-               $this->runOnTransactionIdleCallbacks();
+
+               $this->runOnTransactionIdleCallbacks( self::TRIGGER_COMMIT );
+               $this->runTransactionListenerCallbacks( self::TRIGGER_COMMIT );
        }
 
        /**
@@ -2738,28 +2991,37 @@ abstract class DatabaseBase implements IDatabase {
        }
 
        final public function rollback( $fname = __METHOD__, $flush = '' ) {
-               if ( $flush !== 'flush' ) {
+               if ( $flush === self::FLUSHING_INTERNAL || $flush === self::FLUSHING_ALL_PEERS ) {
                        if ( !$this->mTrxLevel ) {
-                               wfWarn( "$fname: No transaction to rollback, something got out of sync!" );
                                return; // nothing to do
                        }
                } else {
                        if ( !$this->mTrxLevel ) {
+                               $this->queryLogger->error(
+                                       "$fname: No transaction to rollback, something got out of sync." );
                                return; // nothing to do
+                       } elseif ( $this->getFlag( DBO_TRX ) ) {
+                               throw new DBUnexpectedError(
+                                       $this,
+                                       "$fname: Expected mass rollback of all peer databases (DBO_TRX set)."
+                               );
                        }
                }
 
-               # Avoid fatals if close() was called
+               // Avoid fatals if close() was called
                $this->assertOpen();
 
                $this->doRollback( $fname );
-               $this->mTrxIdleCallbacks = []; // cancel
-               $this->mTrxPreCommitCallbacks = []; // cancel
                $this->mTrxAtomicLevels = [];
                if ( $this->mTrxDoneWrites ) {
-                       $this->getTransactionProfiler()->transactionWritingOut(
+                       $this->trxProfiler->transactionWritingOut(
                                $this->mServer, $this->mDBname, $this->mTrxShortId );
                }
+
+               $this->mTrxIdleCallbacks = []; // clear
+               $this->mTrxPreCommitCallbacks = []; // clear
+               $this->runOnTransactionIdleCallbacks( self::TRIGGER_ROLLBACK );
+               $this->runTransactionListenerCallbacks( self::TRIGGER_ROLLBACK );
        }
 
        /**
@@ -2770,11 +3032,29 @@ abstract class DatabaseBase implements IDatabase {
         */
        protected function doRollback( $fname ) {
                if ( $this->mTrxLevel ) {
-                       $this->query( 'ROLLBACK', $fname, true );
+                       # Disconnects cause rollback anyway, so ignore those errors
+                       $ignoreErrors = true;
+                       $this->query( 'ROLLBACK', $fname, $ignoreErrors );
                        $this->mTrxLevel = 0;
                }
        }
 
+       public function flushSnapshot( $fname = __METHOD__ ) {
+               if ( $this->writesOrCallbacksPending() || $this->explicitTrxActive() ) {
+                       // This only flushes transactions to clear snapshots, not to write data
+                       throw new DBUnexpectedError(
+                               $this,
+                               "$fname: Cannot COMMIT to clear snapshot because writes are pending."
+                       );
+               }
+
+               $this->commit( $fname, self::FLUSHING_INTERNAL );
+       }
+
+       public function explicitTrxActive() {
+               return $this->mTrxLevel && ( $this->mTrxAtomicLevels || !$this->mTrxAutomatic );
+       }
+
        /**
         * Creates a new table with structure copied from existing table
         * Note that unlike most database abstraction functions, this function does not
@@ -2787,18 +3067,17 @@ abstract class DatabaseBase implements IDatabase {
         * @param string $newName Name of table to be created
         * @param bool $temporary Whether the new table should be temporary
         * @param string $fname Calling function name
-        * @throws MWException
+        * @throws RuntimeException
         * @return bool True if operation was successful
         */
        public function duplicateTableStructure( $oldName, $newName, $temporary = false,
                $fname = __METHOD__
        ) {
-               throw new MWException(
-                       'DatabaseBase::duplicateTableStructure is not implemented in descendant class' );
+               throw new RuntimeException( __METHOD__ . ' is not implemented in descendant class' );
        }
 
        function listTables( $prefix = null, $fname = __METHOD__ ) {
-               throw new MWException( 'DatabaseBase::listTables is not implemented in descendant class' );
+               throw new RuntimeException( __METHOD__ . ' is not implemented in descendant class' );
        }
 
        /**
@@ -2817,24 +3096,24 @@ abstract class DatabaseBase implements IDatabase {
         *
         * @param string $prefix Only show VIEWs with this prefix, eg. unit_test_
         * @param string $fname Name of calling function
-        * @throws MWException
+        * @throws RuntimeException
         * @return array
         * @since 1.22
         */
        public function listViews( $prefix = null, $fname = __METHOD__ ) {
-               throw new MWException( 'DatabaseBase::listViews is not implemented in descendant class' );
+               throw new RuntimeException( __METHOD__ . ' is not implemented in descendant class' );
        }
 
        /**
         * Differentiates between a TABLE and a VIEW
         *
         * @param string $name Name of the database-structure to test.
-        * @throws MWException
+        * @throws RuntimeException
         * @return bool
         * @since 1.22
         */
        public function isView( $name ) {
-               throw new MWException( 'DatabaseBase::isView is not implemented in descendant class' );
+               throw new RuntimeException( __METHOD__ . ' is not implemented in descendant class' );
        }
 
        public function timestamp( $ts = 0 ) {
@@ -2875,9 +3154,43 @@ abstract class DatabaseBase implements IDatabase {
                }
        }
 
-       public function ping() {
-               # Stub. Not essential to override.
-               return true;
+       public function ping( &$rtt = null ) {
+               // Avoid hitting the server if it was hit recently
+               if ( $this->isOpen() && ( microtime( true ) - $this->lastPing ) < self::PING_TTL ) {
+                       if ( !func_num_args() || $this->mRTTEstimate > 0 ) {
+                               $rtt = $this->mRTTEstimate;
+                               return true; // don't care about $rtt
+                       }
+               }
+
+               // This will reconnect if possible or return false if not
+               $this->clearFlag( DBO_TRX, self::REMEMBER_PRIOR );
+               $ok = ( $this->query( self::PING_QUERY, __METHOD__, true ) !== false );
+               $this->restoreFlags( self::RESTORE_PRIOR );
+
+               if ( $ok ) {
+                       $rtt = $this->mRTTEstimate;
+               }
+
+               return $ok;
+       }
+
+       /**
+        * @return bool
+        */
+       protected function reconnect() {
+               $this->closeConnection();
+               $this->mOpened = false;
+               $this->mConn = false;
+               try {
+                       $this->open( $this->mServer, $this->mUser, $this->mPassword, $this->mDBname );
+                       $this->lastPing = microtime( true );
+                       $ok = true;
+               } catch ( DBConnectionError $e ) {
+                       $ok = false;
+               }
+
+               return $ok;
        }
 
        public function getSessionLagStatus() {
@@ -2885,7 +3198,7 @@ abstract class DatabaseBase implements IDatabase {
        }
 
        /**
-        * Get the slave lag when the current transaction started
+        * Get the replica DB lag when the current transaction started
         *
         * This is useful when transactions might use snapshot isolation
         * (e.g. REPEATABLE-READ in innodb), so the "real" lag of that data
@@ -2897,19 +3210,19 @@ abstract class DatabaseBase implements IDatabase {
         */
        public function getTransactionLagStatus() {
                return $this->mTrxLevel
-                       ? [ 'lag' => $this->mTrxSlaveLag, 'since' => $this->trxTimestamp() ]
+                       ? [ 'lag' => $this->mTrxReplicaLag, 'since' => $this->trxTimestamp() ]
                        : null;
        }
 
        /**
-        * Get a slave lag estimate for this server
+        * Get a replica DB lag estimate for this server
         *
         * @return array ('lag': seconds or false on error, 'since': UNIX timestamp of estimate)
         * @since 1.27
         */
        public function getApproximateLagStatus() {
                return [
-                       'lag'   => $this->getLBInfo( 'slave' ) ? $this->getLag() : 0,
+                       'lag'   => $this->getLBInfo( 'replica' ) ? $this->getLag() : 0,
                        'since' => microtime( true )
                ];
        }
@@ -2984,8 +3297,8 @@ abstract class DatabaseBase implements IDatabase {
         *   generated dynamically using $filename
         * @param bool|callable $inputCallback Optional function called for each
         *   complete line sent
-        * @throws Exception|MWException
         * @return bool|string
+        * @throws Exception
         */
        public function sourceFile(
                $filename, $lineCallback = false, $resultCallback = false, $fname = false, $inputCallback = false
@@ -2995,7 +3308,7 @@ abstract class DatabaseBase implements IDatabase {
                MediaWiki\restoreWarnings();
 
                if ( false === $fp ) {
-                       throw new MWException( "Could not open \"{$filename}\".\n" );
+                       throw new RuntimeException( "Could not open \"{$filename}\".\n" );
                }
 
                if ( !$fname ) {
@@ -3014,25 +3327,6 @@ abstract class DatabaseBase implements IDatabase {
                return $error;
        }
 
-       /**
-        * Get the full path of a patch file. Originally based on archive()
-        * from updaters.inc. Keep in mind this always returns a patch, as
-        * it fails back to MySQL if no DB-specific patch can be found
-        *
-        * @param string $patch The name of the patch, like patch-something.sql
-        * @return string Full path to patch file
-        */
-       public function patchPath( $patch ) {
-               global $IP;
-
-               $dbType = $this->getType();
-               if ( file_exists( "$IP/maintenance/$dbType/archives/$patch" ) ) {
-                       return "$IP/maintenance/$dbType/archives/$patch";
-               } else {
-                       return "$IP/maintenance/archives/$patch";
-               }
-       }
-
        public function setSchemaVars( $vars ) {
                $this->mSchemaVars = $vars;
        }
@@ -3215,16 +3509,35 @@ abstract class DatabaseBase implements IDatabase {
        }
 
        public function getScopedLockAndFlush( $lockKey, $fname, $timeout ) {
+               if ( $this->writesOrCallbacksPending() ) {
+                       // This only flushes transactions to clear snapshots, not to write data
+                       throw new DBUnexpectedError(
+                               $this,
+                               "$fname: Cannot COMMIT to clear snapshot because writes are pending."
+                       );
+               }
+
                if ( !$this->lock( $lockKey, $fname, $timeout ) ) {
                        return null;
                }
 
                $unlocker = new ScopedCallback( function () use ( $lockKey, $fname ) {
-                       $this->commit( __METHOD__, 'flush' );
-                       $this->unlock( $lockKey, $fname );
+                       if ( $this->trxLevel() ) {
+                               // There is a good chance an exception was thrown, causing any early return
+                               // from the caller. Let any error handler get a chance to issue rollback().
+                               // If there isn't one, let the error bubble up and trigger server-side rollback.
+                               $this->onTransactionResolution(
+                                       function () use ( $lockKey, $fname ) {
+                                               $this->unlock( $lockKey, $fname );
+                                       },
+                                       $fname
+                               );
+                       } else {
+                               $this->unlock( $lockKey, $fname );
+                       }
                } );
 
-               $this->commit( __METHOD__, 'flush' );
+               $this->commit( $fname, self::FLUSHING_INTERNAL );
 
                return $unlocker;
        }
@@ -3318,6 +3631,10 @@ abstract class DatabaseBase implements IDatabase {
                return is_string( $reason ) ? $reason : false;
        }
 
+       public function setTableAliases( array $aliases ) {
+               $this->tableAliases = $aliases;
+       }
+
        /**
         * @since 1.19
         * @return string
@@ -3333,9 +3650,14 @@ abstract class DatabaseBase implements IDatabase {
                if ( $this->mTrxLevel && $this->mTrxDoneWrites ) {
                        trigger_error( "Uncommitted DB writes (transaction from {$this->mTrxFname})." );
                }
-               if ( count( $this->mTrxIdleCallbacks ) || count( $this->mTrxPreCommitCallbacks ) ) {
+               $danglingCallbacks = array_merge(
+                       $this->mTrxIdleCallbacks,
+                       $this->mTrxPreCommitCallbacks,
+                       $this->mTrxEndCallbacks
+               );
+               if ( $danglingCallbacks ) {
                        $callers = [];
-                       foreach ( $this->mTrxIdleCallbacks as $callbackInfo ) {
+                       foreach ( $danglingCallbacks as $callbackInfo ) {
                                $callers[] = $callbackInfo[1];
                        }
                        $callers = implode( ', ', $callers );