Merge "rdbms: clean up DBO_TRX behavior for onTransactionPreCommitOrIdle()"
[lhc/web/wiklou.git] / includes / libs / rdbms / database / Database.php
index 572a798..417f64c 100644 (file)
@@ -27,11 +27,13 @@ namespace Wikimedia\Rdbms;
 
 use Psr\Log\LoggerAwareInterface;
 use Psr\Log\LoggerInterface;
+use Psr\Log\NullLogger;
 use Wikimedia\ScopedCallback;
 use Wikimedia\Timestamp\ConvertibleTimestamp;
 use Wikimedia;
 use BagOStuff;
 use HashBagOStuff;
+use LogicException;
 use InvalidArgumentException;
 use Exception;
 use RuntimeException;
@@ -58,27 +60,38 @@ abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAware
        const SLOW_WRITE_SEC = 0.500;
        const SMALL_WRITE_ROWS = 100;
 
+       /** @var string Whether lock granularity is on the level of the entire database */
+       const ATTR_DB_LEVEL_LOCKING = 'db-level-locking';
+
+       /** @var int New Database instance will not be connected yet when returned */
+       const NEW_UNCONNECTED = 0;
+       /** @var int New Database instance will already be connected when returned */
+       const NEW_CONNECTED = 1;
+
        /** @var string SQL query */
        protected $lastQuery = '';
        /** @var float|bool UNIX timestamp of last write query */
        protected $lastWriteTime = false;
        /** @var string|bool */
        protected $phpError = false;
-       /** @var string */
+       /** @var string Server that this instance is currently connected to */
        protected $server;
-       /** @var string */
+       /** @var string User that this instance is currently connected under the name of */
        protected $user;
-       /** @var string */
+       /** @var string Password used to establish the current connection */
        protected $password;
-       /** @var string */
+       /** @var string Database that this instance is currently connected to */
        protected $dbName;
-       /** @var array[] $aliases Map of (table => (dbname, schema, prefix) map) */
+       /** @var array[] Map of (table => (dbname, schema, prefix) map) */
        protected $tableAliases = [];
+       /** @var string[] Map of (index alias => index) */
+       protected $indexAliases = [];
        /** @var bool Whether this PHP instance is for a CLI script */
        protected $cliMode;
        /** @var string Agent name for query profiling */
        protected $agent;
-
+       /** @var array Parameters used by initConnection() to establish a connection */
+       protected $connectionParams = [];
        /** @var BagOStuff APC cache */
        protected $srvCache;
        /** @var LoggerInterface */
@@ -236,19 +249,17 @@ abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAware
        /** @var TransactionProfiler */
        protected $trxProfiler;
 
+       /** @var int */
+       protected $nonNativeInsertSelectBatchSize = 10000;
+
        /**
-        * Constructor and database handle and attempt to connect to the DB server
-        *
-        * IDatabase classes should not be constructed directly in external
-        * code. Database::factory() should be used instead.
-        *
+        * @note: exceptions for missing libraries/drivers should be thrown in initConnection()
         * @param array $params Parameters passed from Database::factory()
         */
-       function __construct( array $params ) {
-               $server = $params['host'];
-               $user = $params['user'];
-               $password = $params['password'];
-               $dbName = $params['dbname'];
+       protected function __construct( array $params ) {
+               foreach ( [ 'host', 'user', 'password', 'dbname' ] as $name ) {
+                       $this->connectionParams[$name] = $params[$name];
+               }
 
                $this->schema = $params['schema'];
                $this->tablePrefix = $params['tablePrefix'];
@@ -278,15 +289,28 @@ abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAware
                $this->queryLogger = $params['queryLogger'];
                $this->errorLogger = $params['errorLogger'];
 
+               if ( isset( $params['nonNativeInsertSelectBatchSize'] ) ) {
+                       $this->nonNativeInsertSelectBatchSize = $params['nonNativeInsertSelectBatchSize'];
+               }
+
                // Set initial dummy domain until open() sets the final DB/prefix
                $this->currentDomain = DatabaseDomain::newUnspecified();
+       }
 
-               if ( $user ) {
-                       $this->open( $server, $user, $password, $dbName );
-               } elseif ( $this->requiresDatabaseUser() ) {
-                       throw new InvalidArgumentException( "No database user provided." );
+       /**
+        * Initialize the connection to the database over the wire (or to local files)
+        *
+        * @throws LogicException
+        * @throws InvalidArgumentException
+        * @throws DBConnectionError
+        * @since 1.31
+        */
+       final public function initConnection() {
+               if ( $this->isOpen() ) {
+                       throw new LogicException( __METHOD__ . ': already connected.' );
                }
-
+               // Establish the connection
+               $this->doInitConnection();
                // Set the domain object after open() sets the relevant fields
                if ( $this->dbName != '' ) {
                        // Domains with server scope but a table prefix are not used by IDatabase classes
@@ -294,12 +318,32 @@ abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAware
                }
        }
 
+       /**
+        * Actually connect to the database over the wire (or to local files)
+        *
+        * @throws InvalidArgumentException
+        * @throws DBConnectionError
+        * @since 1.31
+        */
+       protected function doInitConnection() {
+               if ( strlen( $this->connectionParams['user'] ) ) {
+                       $this->open(
+                               $this->connectionParams['host'],
+                               $this->connectionParams['user'],
+                               $this->connectionParams['password'],
+                               $this->connectionParams['dbname']
+                       );
+               } else {
+                       throw new InvalidArgumentException( "No database user provided." );
+               }
+       }
+
        /**
         * Construct a Database subclass instance given a database type and parameters
         *
         * This also connects to the database immediately upon object construction
         *
-        * @param string $dbType A possible DB type (sqlite, mysql, postgres)
+        * @param string $dbType A possible DB type (sqlite, mysql, postgres,...)
         * @param array $p Parameter map with keys:
         *   - host : The hostname of the DB server
         *   - user : The name of the database user the client operates under
@@ -331,11 +375,79 @@ abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAware
         *   - cliMode: Whether to consider the execution context that of a CLI script.
         *   - agent: Optional name used to identify the end-user in query profiling/logging.
         *   - srvCache: Optional BagOStuff instance to an APC-style cache.
+        *   - nonNativeInsertSelectBatchSize: Optional batch size for non-native INSERT SELECT emulation.
+        * @param int $connect One of the class constants (NEW_CONNECTED, NEW_UNCONNECTED) [optional]
         * @return Database|null If the database driver or extension cannot be found
         * @throws InvalidArgumentException If the database driver or extension cannot be found
         * @since 1.18
         */
-       final public static function factory( $dbType, $p = [] ) {
+       final public static function factory( $dbType, $p = [], $connect = self::NEW_CONNECTED ) {
+               $class = self::getClass( $dbType, isset( $p['driver'] ) ? $p['driver'] : null );
+
+               if ( class_exists( $class ) && is_subclass_of( $class, IDatabase::class ) ) {
+                       // 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'] : '';
+                       $p['schema'] = isset( $p['schema'] ) ? $p['schema'] : '';
+                       $p['cliMode'] = isset( $p['cliMode'] )
+                               ? $p['cliMode']
+                               : ( PHP_SAPI === 'cli' || PHP_SAPI === 'phpdbg' );
+                       $p['agent'] = isset( $p['agent'] ) ? $p['agent'] : '';
+                       if ( !isset( $p['connLogger'] ) ) {
+                               $p['connLogger'] = new NullLogger();
+                       }
+                       if ( !isset( $p['queryLogger'] ) ) {
+                               $p['queryLogger'] = new NullLogger();
+                       }
+                       $p['profiler'] = isset( $p['profiler'] ) ? $p['profiler'] : null;
+                       if ( !isset( $p['trxProfiler'] ) ) {
+                               $p['trxProfiler'] = new TransactionProfiler();
+                       }
+                       if ( !isset( $p['errorLogger'] ) ) {
+                               $p['errorLogger'] = function ( Exception $e ) {
+                                       trigger_error( get_class( $e ) . ': ' . $e->getMessage(), E_USER_WARNING );
+                               };
+                       }
+
+                       /** @var Database $conn */
+                       $conn = new $class( $p );
+                       if ( $connect == self::NEW_CONNECTED ) {
+                               $conn->initConnection();
+                       }
+               } else {
+                       $conn = null;
+               }
+
+               return $conn;
+       }
+
+       /**
+        * @param string $dbType A possible DB type (sqlite, mysql, postgres,...)
+        * @param string|null $driver Optional name of a specific DB client driver
+        * @return array Map of (Database::ATTRIBUTE_* constant => value) for all such constants
+        * @throws InvalidArgumentException
+        * @since 1.31
+        */
+       final public static function attributesFromType( $dbType, $driver = null ) {
+               static $defaults = [ self::ATTR_DB_LEVEL_LOCKING => false ];
+
+               $class = self::getClass( $dbType, $driver );
+
+               return call_user_func( [ $class, 'getAttributes' ] ) + $defaults;
+       }
+
+       /**
+        * @param string $dbType A possible DB type (sqlite, mysql, postgres,...)
+        * @param string|null $driver Optional name of a specific DB client driver
+        * @return string Database subclass name to use
+        * @throws InvalidArgumentException
+        */
+       private static function getClass( $dbType, $driver = null ) {
                // For database types with built-in support, the below maps type to IDatabase
                // implementations. For types with multipe driver implementations (PHP extensions),
                // an array can be used, keyed by extension name. In case of an array, the
@@ -351,17 +463,18 @@ abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAware
 
                $dbType = strtolower( $dbType );
                $class = false;
+
                if ( isset( $builtinTypes[$dbType] ) ) {
                        $possibleDrivers = $builtinTypes[$dbType];
                        if ( is_string( $possibleDrivers ) ) {
                                $class = $possibleDrivers;
                        } else {
-                               if ( !empty( $p['driver'] ) ) {
-                                       if ( !isset( $possibleDrivers[$p['driver']] ) ) {
+                               if ( (string)$driver !== '' ) {
+                                       if ( !isset( $possibleDrivers[$driver] ) ) {
                                                throw new InvalidArgumentException( __METHOD__ .
-                                                       " type '$dbType' does not support driver '{$p['driver']}'" );
+                                                       " type '$dbType' does not support driver '{$driver}'" );
                                        } else {
-                                               $class = $possibleDrivers[$p['driver']];
+                                               $class = $possibleDrivers[$driver];
                                        }
                                } else {
                                        foreach ( $possibleDrivers as $posDriver => $possibleClass ) {
@@ -381,42 +494,15 @@ abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAware
                                " no viable database extension found for type '$dbType'" );
                }
 
-               if ( class_exists( $class ) && is_subclass_of( $class, IDatabase::class ) ) {
-                       // 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'] : '';
-                       $p['schema'] = isset( $p['schema'] ) ? $p['schema'] : '';
-                       $p['cliMode'] = isset( $p['cliMode'] )
-                               ? $p['cliMode']
-                               : ( PHP_SAPI === 'cli' || PHP_SAPI === 'phpdbg' );
-                       $p['agent'] = isset( $p['agent'] ) ? $p['agent'] : '';
-                       if ( !isset( $p['connLogger'] ) ) {
-                               $p['connLogger'] = new \Psr\Log\NullLogger();
-                       }
-                       if ( !isset( $p['queryLogger'] ) ) {
-                               $p['queryLogger'] = new \Psr\Log\NullLogger();
-                       }
-                       $p['profiler'] = isset( $p['profiler'] ) ? $p['profiler'] : null;
-                       if ( !isset( $p['trxProfiler'] ) ) {
-                               $p['trxProfiler'] = new TransactionProfiler();
-                       }
-                       if ( !isset( $p['errorLogger'] ) ) {
-                               $p['errorLogger'] = function ( Exception $e ) {
-                                       trigger_error( get_class( $e ) . ': ' . $e->getMessage(), E_USER_WARNING );
-                               };
-                       }
-
-                       $conn = new $class( $p );
-               } else {
-                       $conn = null;
-               }
+               return $class;
+       }
 
-               return $conn;
+       /**
+        * @return array Map of (Database::ATTRIBUTE_* constant => value
+        * @since 1.31
+        */
+       protected static function getAttributes() {
+               return [];
        }
 
        /**
@@ -559,7 +645,10 @@ abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAware
 
        public function writesOrCallbacksPending() {
                return $this->trxLevel && (
-                       $this->trxDoneWrites || $this->trxIdleCallbacks || $this->trxPreCommitCallbacks
+                       $this->trxDoneWrites ||
+                       $this->trxIdleCallbacks ||
+                       $this->trxPreCommitCallbacks ||
+                       $this->trxEndCallbacks
                );
        }
 
@@ -762,21 +851,38 @@ abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAware
 
        public function close() {
                if ( $this->conn ) {
+                       // Resolve any dangling transaction first
                        if ( $this->trxLevel() ) {
+                               // Meaningful transactions should ideally have been resolved by now
+                               if ( $this->writesOrCallbacksPending() ) {
+                                       $this->queryLogger->warning(
+                                               __METHOD__ . ": writes or callbacks still pending.",
+                                               [ 'trace' => ( new RuntimeException() )->getTraceAsString() ]
+                                       );
+                               }
+                               // Check if it is possible to properly commit and trigger callbacks
+                               if ( $this->trxEndCallbacksSuppressed ) {
+                                       throw new DBUnexpectedError(
+                                               $this,
+                                               __METHOD__ . ': callbacks are suppressed; cannot properly commit.'
+                                       );
+                               }
+                               // Commit the changes and run any callbacks as needed
                                $this->commit( __METHOD__, self::FLUSHING_INTERNAL );
                        }
-
+                       // Close the actual connection in the binding handle
                        $closed = $this->closeConnection();
                        $this->conn = false;
-               } elseif (
-                       $this->trxIdleCallbacks ||
-                       $this->trxPreCommitCallbacks ||
-                       $this->trxEndCallbacks
-               ) { // sanity
-                       throw new RuntimeException( "Transaction callbacks still pending." );
+                       // Sanity check that no callbacks are dangling
+                       if (
+                               $this->trxIdleCallbacks || $this->trxPreCommitCallbacks || $this->trxEndCallbacks
+                       ) {
+                               throw new RuntimeException( "Transaction callbacks still pending." );
+                       }
                } else {
-                       $closed = true;
+                       $closed = true; // already closed; nothing to do
                }
+
                $this->opened = false;
 
                return $closed;
@@ -811,11 +917,13 @@ abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAware
        }
 
        /**
-        * The DBMS-dependent part of query()
+        * Run a query and return a DBMS-dependent wrapper (that has all IResultWrapper methods)
+        *
+        * This might return things, such as mysqli_result, that do not formally implement
+        * IResultWrapper, but nonetheless implement all of its methods correctly
         *
         * @param string $sql SQL query.
-        * @return ResultWrapper|bool Result object to feed to fetchObject,
-        *   fetchRow, ...; or false on failure
+        * @return IResultWrapper|bool Iterator to feed to fetchObject/fetchRow; false on failure
         */
        abstract protected function doQuery( $sql );
 
@@ -953,7 +1061,7 @@ abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAware
                $ret = $this->doProfiledQuery( $sql, $commentedSql, $isNonTempWrite, $fname );
 
                # Try reconnecting if the connection was lost
-               if ( false === $ret && $this->wasErrorReissuable() ) {
+               if ( false === $ret && $this->wasConnectionLoss() ) {
                        $recoverable = $this->canRecoverFromDisconnect( $sql, $priorWritesPending );
                        # Stash the last error values before anything might clear them
                        $lastError = $this->lastError();
@@ -967,12 +1075,12 @@ abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAware
                                $this->queryLogger->warning( $msg, $params +
                                        [ 'trace' => ( new RuntimeException() )->getTraceAsString() ] );
 
-                               if ( !$recoverable ) {
-                                       # Callers may catch the exception and continue to use the DB
-                                       $this->reportQueryError( $lastError, $lastErrno, $sql, $fname );
-                               } else {
+                               if ( $recoverable ) {
                                        # Should be safe to silently retry the query
                                        $ret = $this->doProfiledQuery( $sql, $commentedSql, $isNonTempWrite, $fname );
+                               } else {
+                                       # Callers may catch the exception and continue to use the DB
+                                       $this->reportQueryError( $lastError, $lastErrno, $sql, $fname );
                                }
                        } else {
                                $msg = __METHOD__ . ': lost connection to {dbserver} permanently';
@@ -1133,19 +1241,29 @@ abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAware
         */
        private function handleSessionLoss() {
                $this->trxLevel = 0;
-               $this->trxIdleCallbacks = []; // T67263
-               $this->trxPreCommitCallbacks = []; // T67263
+               $this->trxIdleCallbacks = []; // T67263; transaction already lost
+               $this->trxPreCommitCallbacks = []; // T67263; transaction already lost
                $this->sessionTempTables = [];
                $this->namedLocksHeld = [];
+
+               // Note: if callback suppression is set then some *Callbacks arrays are not cleared here
+               $e = null;
                try {
                        // Handle callbacks in trxEndCallbacks
                        $this->runOnTransactionIdleCallbacks( self::TRIGGER_ROLLBACK );
+               } catch ( Exception $ex ) {
+                       // Already logged; move on...
+                       $e = $e ?: $ex;
+               }
+               try {
+                       // Handle callbacks in trxRecurringCallbacks
                        $this->runTransactionListenerCallbacks( self::TRIGGER_ROLLBACK );
-                       return null;
-               } catch ( Exception $e ) {
+               } catch ( Exception $ex ) {
                        // Already logged; move on...
-                       return $e;
+                       $e = $e ?: $ex;
                }
+
+               return $e;
        }
 
        /**
@@ -1413,14 +1531,27 @@ abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAware
                list( $startOpts, $useIndex, $preLimitTail, $postLimitTail, $ignoreIndex ) =
                        $this->makeSelectOptions( $options );
 
-               if ( !empty( $conds ) ) {
-                       if ( is_array( $conds ) ) {
-                               $conds = $this->makeList( $conds, self::LIST_AND );
-                       }
+               if ( is_array( $conds ) ) {
+                       $conds = $this->makeList( $conds, self::LIST_AND );
+               }
+
+               if ( $conds === null || $conds === false ) {
+                       $this->queryLogger->warning(
+                               __METHOD__
+                               . ' called from '
+                               . $fname
+                               . ' with incorrect parameters: $conds must be a string or an array'
+                       );
+                       $conds = '';
+               }
+
+               if ( $conds === '' ) {
+                       $sql = "SELECT $startOpts $vars $from $useIndex $ignoreIndex $preLimitTail";
+               } elseif ( is_string( $conds ) ) {
                        $sql = "SELECT $startOpts $vars $from $useIndex $ignoreIndex " .
                                "WHERE $conds $preLimitTail";
                } else {
-                       $sql = "SELECT $startOpts $vars $from $useIndex $ignoreIndex $preLimitTail";
+                       throw new DBUnexpectedError( $this, __METHOD__ . ' called with incorrect parameters' );
                }
 
                if ( isset( $options['LIMIT'] ) ) {
@@ -1457,35 +1588,93 @@ abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAware
        }
 
        public function estimateRowCount(
-               $table, $vars = '*', $conds = '', $fname = __METHOD__, $options = []
+               $table, $var = '*', $conds = '', $fname = __METHOD__, $options = [], $join_conds = []
        ) {
-               $rows = 0;
-               $res = $this->select( $table, [ 'rowcount' => 'COUNT(*)' ], $conds, $fname, $options );
-
-               if ( $res ) {
-                       $row = $this->fetchRow( $res );
-                       $rows = ( isset( $row['rowcount'] ) ) ? (int)$row['rowcount'] : 0;
+               $conds = $this->normalizeConditions( $conds, $fname );
+               $column = $this->extractSingleFieldFromList( $var );
+               if ( is_string( $column ) && !in_array( $column, [ '*', '1' ] ) ) {
+                       $conds[] = "$column IS NOT NULL";
                }
 
-               return $rows;
+               $res = $this->select(
+                       $table, [ 'rowcount' => 'COUNT(*)' ], $conds, $fname, $options, $join_conds
+               );
+               $row = $res ? $this->fetchRow( $res ) : [];
+
+               return isset( $row['rowcount'] ) ? (int)$row['rowcount'] : 0;
        }
 
        public function selectRowCount(
-               $tables, $vars = '*', $conds = '', $fname = __METHOD__, $options = [], $join_conds = []
+               $tables, $var = '*', $conds = '', $fname = __METHOD__, $options = [], $join_conds = []
        ) {
-               $rows = 0;
-               $sql = $this->selectSQLText( $tables, '1', $conds, $fname, $options, $join_conds );
-               // The identifier quotes is primarily for MSSQL.
-               $rowCountCol = $this->addIdentifierQuotes( "rowcount" );
-               $tableName = $this->addIdentifierQuotes( "tmp_count" );
-               $res = $this->query( "SELECT COUNT(*) AS $rowCountCol FROM ($sql) $tableName", $fname );
+               $conds = $this->normalizeConditions( $conds, $fname );
+               $column = $this->extractSingleFieldFromList( $var );
+               if ( is_string( $column ) && !in_array( $column, [ '*', '1' ] ) ) {
+                       $conds[] = "$column IS NOT NULL";
+               }
+
+               $res = $this->select(
+                       [
+                               'tmp_count' => $this->buildSelectSubquery(
+                                       $tables,
+                                       '1',
+                                       $conds,
+                                       $fname,
+                                       $options,
+                                       $join_conds
+                               )
+                       ],
+                       [ 'rowcount' => 'COUNT(*)' ],
+                       [],
+                       $fname
+               );
+               $row = $res ? $this->fetchRow( $res ) : [];
 
-               if ( $res ) {
-                       $row = $this->fetchRow( $res );
-                       $rows = ( isset( $row['rowcount'] ) ) ? (int)$row['rowcount'] : 0;
+               return isset( $row['rowcount'] ) ? (int)$row['rowcount'] : 0;
+       }
+
+       /**
+        * @param array|string $conds
+        * @param string $fname
+        * @return array
+        */
+       final protected function normalizeConditions( $conds, $fname ) {
+               if ( $conds === null || $conds === false ) {
+                       $this->queryLogger->warning(
+                               __METHOD__
+                               . ' called from '
+                               . $fname
+                               . ' with incorrect parameters: $conds must be a string or an array'
+                       );
+                       $conds = '';
                }
 
-               return $rows;
+               if ( !is_array( $conds ) ) {
+                       $conds = ( $conds === '' ) ? [] : [ $conds ];
+               }
+
+               return $conds;
+       }
+
+       /**
+        * @param array|string $var Field parameter in the style of select()
+        * @return string|null Column name or null; ignores aliases
+        * @throws DBUnexpectedError Errors out if multiple columns are given
+        */
+       final protected function extractSingleFieldFromList( $var ) {
+               if ( is_array( $var ) ) {
+                       if ( !$var ) {
+                               $column = null;
+                       } elseif ( count( $var ) == 1 ) {
+                               $column = isset( $var[0] ) ? $var[0] : reset( $var );
+                       } else {
+                               throw new DBUnexpectedError( $this, __METHOD__ . ': got multiple columns.' );
+                       }
+               } else {
+                       $column = $var;
+               }
+
+               return $column;
        }
 
        /**
@@ -1793,10 +1982,57 @@ abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAware
                return '(' . $this->selectSQLText( $table, $fld, $conds, null, [], $join_conds ) . ')';
        }
 
+       public function buildSubstring( $input, $startPosition, $length = null ) {
+               $this->assertBuildSubstringParams( $startPosition, $length );
+               $functionBody = "$input FROM $startPosition";
+               if ( $length !== null ) {
+                       $functionBody .= " FOR $length";
+               }
+               return 'SUBSTRING(' . $functionBody . ')';
+       }
+
+       /**
+        * Check type and bounds for parameters to self::buildSubstring()
+        *
+        * All supported databases have substring functions that behave the same for
+        * positive $startPosition and non-negative $length, but behaviors differ when
+        * given 0 or negative $startPosition or negative $length. The simplest
+        * solution to that is to just forbid those values.
+        *
+        * @param int $startPosition
+        * @param int|null $length
+        * @since 1.31
+        */
+       protected function assertBuildSubstringParams( $startPosition, $length ) {
+               if ( !is_int( $startPosition ) || $startPosition <= 0 ) {
+                       throw new InvalidArgumentException(
+                               '$startPosition must be a positive integer'
+                       );
+               }
+               if ( !( is_int( $length ) && $length >= 0 || $length === null ) ) {
+                       throw new InvalidArgumentException(
+                               '$length must be null or an integer greater than or equal to 0'
+                       );
+               }
+       }
+
        public function buildStringCast( $field ) {
                return $field;
        }
 
+       public function buildIntegerCast( $field ) {
+               return 'CAST( ' . $field . ' AS INTEGER )';
+       }
+
+       public function buildSelectSubquery(
+               $table, $vars, $conds = '', $fname = __METHOD__,
+               $options = [], $join_conds = []
+       ) {
+               return new Subquery(
+                       $this->selectSQLText( $table, $vars, $conds, $fname, $options, $join_conds )
+               );
+       }
+
        public function databasesAreIndependent() {
                return false;
        }
@@ -1819,6 +2055,13 @@ abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAware
        }
 
        public function tableName( $name, $format = 'quoted' ) {
+               if ( $name instanceof Subquery ) {
+                       throw new DBUnexpectedError(
+                               $this,
+                               __METHOD__ . ': got Subquery instance when expecting a string.'
+                       );
+               }
+
                # Skip the entire process when we have a string quoted on both ends.
                # Note that we check the end so that we will still quote any use of
                # use of `database`.table. But won't break things if someone wants
@@ -1835,6 +2078,11 @@ abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAware
                # any remote case where a word like on may be inside of a table name
                # surrounded by symbols which may be considered word breaks.
                if ( preg_match( '/(^|\s)(DISTINCT|JOIN|ON|AS)(\s|$)/i', $name ) !== 0 ) {
+                       $this->queryLogger->warning(
+                               __METHOD__ . ": use of subqueries is not supported this way.",
+                               [ 'trace' => ( new RuntimeException() )->getTraceAsString() ]
+                       );
+
                        return $name;
                }
 
@@ -1939,17 +2187,32 @@ abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAware
 
        /**
         * Get an aliased table name
-        * e.g. tableName AS newTableName
         *
-        * @param string $name Table name, see tableName()
-        * @param string|bool $alias Alias (optional)
+        * This returns strings like "tableName AS newTableName" for aliased tables
+        * and "(SELECT * from tableA) newTablename" for subqueries (e.g. derived tables)
+        *
+        * @see Database::tableName()
+        * @param string|Subquery $table Table name or object with a 'sql' field
+        * @param string|bool $alias Table alias (optional)
         * @return string SQL name for aliased table. Will not alias a table to its own name
         */
-       protected function tableNameWithAlias( $name, $alias = false ) {
-               if ( !$alias || $alias == $name ) {
-                       return $this->tableName( $name );
+       protected function tableNameWithAlias( $table, $alias = false ) {
+               if ( is_string( $table ) ) {
+                       $quotedTable = $this->tableName( $table );
+               } elseif ( $table instanceof Subquery ) {
+                       $quotedTable = (string)$table;
+               } else {
+                       throw new InvalidArgumentException( "Table must be a string or Subquery." );
+               }
+
+               if ( !strlen( $alias ) || $alias === $table ) {
+                       if ( $table instanceof Subquery ) {
+                               throw new InvalidArgumentException( "Subquery table missing alias." );
+                       }
+
+                       return $quotedTable;
                } else {
-                       return $this->tableName( $name ) . ' ' . $this->addIdentifierQuotes( $alias );
+                       return $quotedTable . ' ' . $this->addIdentifierQuotes( $alias );
                }
        }
 
@@ -2033,9 +2296,9 @@ abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAware
                        if ( is_array( $table ) ) {
                                // A parenthesized group
                                if ( count( $table ) > 1 ) {
-                                       $joinedTable = '('
-                                               . $this->tableNamesWithIndexClauseOrJOIN( $table, $use_index, $ignore_index, $join_conds )
-                                               . ')';
+                                       $joinedTable = '(' .
+                                               $this->tableNamesWithIndexClauseOrJOIN(
+                                                       $table, $use_index, $ignore_index, $join_conds ) . ')';
                                } else {
                                        // Degenerate case
                                        $innerTable = reset( $table );
@@ -2097,8 +2360,8 @@ abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAware
                }
 
                // We can't separate explicit JOIN clauses with ',', use ' ' for those
-               $implicitJoins = !empty( $ret ) ? implode( ',', $ret ) : "";
-               $explicitJoins = !empty( $retJOIN ) ? implode( ' ', $retJOIN ) : "";
+               $implicitJoins = $ret ? implode( ',', $ret ) : "";
+               $explicitJoins = $retJOIN ? implode( ' ', $retJOIN ) : "";
 
                // Compile our final table clause
                return implode( ' ', [ $implicitJoins, $explicitJoins ] );
@@ -2111,7 +2374,9 @@ abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAware
         * @return string
         */
        protected function indexName( $index ) {
-               return $index;
+               return isset( $this->indexAliases[$index] )
+                       ? $this->indexAliases[$index]
+                       : $index;
        }
 
        public function addQuotes( $s ) {
@@ -2191,7 +2456,8 @@ abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAware
                        }
                }
 
-               return ' LIKE ' . $this->addQuotes( $s ) . ' ESCAPE ' . $this->addQuotes( $escapeChar ) . ' ';
+               return ' LIKE ' .
+                       $this->addQuotes( $s ) . ' ESCAPE ' . $this->addQuotes( $escapeChar ) . ' ';
        }
 
        public function anyChar() {
@@ -2244,11 +2510,8 @@ abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAware
                        $rows = [ $rows ];
                }
 
-               $useTrx = !$this->trxLevel;
-               if ( $useTrx ) {
-                       $this->begin( $fname, self::TRANSACTION_INTERNAL );
-               }
                try {
+                       $this->startAtomic( $fname );
                        $affectedRowCount = 0;
                        foreach ( $rows as $row ) {
                                // Delete rows which collide with this one
@@ -2281,17 +2544,12 @@ abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAware
                                $this->insert( $table, $row, $fname );
                                $affectedRowCount += $this->affectedRows();
                        }
+                       $this->endAtomic( $fname );
+                       $this->affectedRowCount = $affectedRowCount;
                } catch ( Exception $e ) {
-                       if ( $useTrx ) {
-                               $this->rollback( $fname, self::FLUSHING_INTERNAL );
-                       }
+                       $this->rollback( $fname, self::FLUSHING_INTERNAL );
                        throw $e;
                }
-               if ( $useTrx ) {
-                       $this->commit( $fname, self::FLUSHING_INTERNAL );
-               }
-
-               $this->affectedRowCount = $affectedRowCount;
        }
 
        /**
@@ -2357,11 +2615,8 @@ abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAware
                }
 
                $affectedRowCount = 0;
-               $useTrx = !$this->trxLevel;
-               if ( $useTrx ) {
-                       $this->begin( $fname, self::TRANSACTION_INTERNAL );
-               }
                try {
+                       $this->startAtomic( $fname );
                        # Update any existing conflicting row(s)
                        if ( $where !== false ) {
                                $ok = $this->update( $table, $set, $where, $fname );
@@ -2372,16 +2627,12 @@ abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAware
                        # Now insert any non-conflicting row(s)
                        $ok = $this->insert( $table, $rows, $fname, [ 'IGNORE' ] ) && $ok;
                        $affectedRowCount += $this->affectedRows();
+                       $this->endAtomic( $fname );
+                       $this->affectedRowCount = $affectedRowCount;
                } catch ( Exception $e ) {
-                       if ( $useTrx ) {
-                               $this->rollback( $fname, self::FLUSHING_INTERNAL );
-                       }
+                       $this->rollback( $fname, self::FLUSHING_INTERNAL );
                        throw $e;
                }
-               if ( $useTrx ) {
-                       $this->commit( $fname, self::FLUSHING_INTERNAL );
-               }
-               $this->affectedRowCount = $affectedRowCount;
 
                return $ok;
        }
@@ -2439,11 +2690,16 @@ abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAware
                return $this->query( $sql, $fname );
        }
 
-       public function insertSelect(
+       final public function insertSelect(
                $destTable, $srcTable, $varMap, $conds,
                $fname = __METHOD__, $insertOptions = [], $selectOptions = [], $selectJoinConds = []
        ) {
-               if ( $this->cliMode ) {
+               static $hints = [ 'NO_AUTO_COLUMNS' ];
+
+               $insertOptions = (array)$insertOptions;
+               $selectOptions = (array)$selectOptions;
+
+               if ( $this->cliMode && $this->isInsertSelectSafe( $insertOptions, $selectOptions ) ) {
                        // 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(
@@ -2452,7 +2708,7 @@ abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAware
                                $varMap,
                                $conds,
                                $fname,
-                               $insertOptions,
+                               array_diff( $insertOptions, $hints ),
                                $selectOptions,
                                $selectJoinConds
                        );
@@ -2464,12 +2720,22 @@ abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAware
                        $varMap,
                        $conds,
                        $fname,
-                       $insertOptions,
+                       array_diff( $insertOptions, $hints ),
                        $selectOptions,
                        $selectJoinConds
                );
        }
 
+       /**
+        * @param array $insertOptions INSERT options
+        * @param array $selectOptions SELECT options
+        * @return bool Whether an INSERT SELECT with these options will be replication safe
+        * @since 1.31
+        */
+       protected function isInsertSelectSafe( array $insertOptions, array $selectOptions ) {
+               return true;
+       }
+
        /**
         * Implementation of insertSelect() based on select() and insert()
         *
@@ -2504,12 +2770,41 @@ abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAware
                        return false;
                }
 
-               $rows = [];
-               foreach ( $res as $row ) {
-                       $rows[] = (array)$row;
+               try {
+                       $affectedRowCount = 0;
+                       $this->startAtomic( $fname );
+                       $rows = [];
+                       $ok = true;
+                       foreach ( $res as $row ) {
+                               $rows[] = (array)$row;
+
+                               // Avoid inserts that are too huge
+                               if ( count( $rows ) >= $this->nonNativeInsertSelectBatchSize ) {
+                                       $ok = $this->insert( $destTable, $rows, $fname, $insertOptions );
+                                       if ( !$ok ) {
+                                               break;
+                                       }
+                                       $affectedRowCount += $this->affectedRows();
+                                       $rows = [];
+                               }
+                       }
+                       if ( $rows && $ok ) {
+                               $ok = $this->insert( $destTable, $rows, $fname, $insertOptions );
+                               if ( $ok ) {
+                                       $affectedRowCount += $this->affectedRows();
+                               }
+                       }
+                       if ( $ok ) {
+                               $this->endAtomic( $fname );
+                               $this->affectedRowCount = $affectedRowCount;
+                       } else {
+                               $this->rollback( $fname, self::FLUSHING_INTERNAL );
+                       }
+                       return $ok;
+               } catch ( Exception $e ) {
+                       $this->rollback( $fname, self::FLUSHING_INTERNAL );
+                       throw $e;
                }
-
-               return $this->insert( $destTable, $rows, $fname, $insertOptions );
        }
 
        /**
@@ -2690,14 +2985,22 @@ abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAware
                return false;
        }
 
-       public function wasErrorReissuable() {
-               return false;
+       public function wasConnectionLoss() {
+               return $this->wasConnectionError( $this->lastErrno() );
        }
 
        public function wasReadOnlyError() {
                return false;
        }
 
+       public function wasErrorReissuable() {
+               return (
+                       $this->wasDeadlock() ||
+                       $this->wasLockTimeout() ||
+                       $this->wasConnectionLoss()
+               );
+       }
+
        /**
         * Do not use this method outside of Database/DBError classes
         *
@@ -2979,16 +3282,12 @@ abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAware
                                $msg = "$fname: Explicit transaction already active (from {$this->trxFname}).";
                                throw new DBUnexpectedError( $this, $msg );
                        } else {
-                               // @TODO: make this an exception at some point
                                $msg = "$fname: Implicit transaction already active (from {$this->trxFname}).";
-                               $this->queryLogger->error( $msg );
-                               return; // join the main transaction set
+                               throw new DBUnexpectedError( $this, $msg );
                        }
                } elseif ( $this->getFlag( self::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
+                       throw new DBUnexpectedError( $this, $msg );
                }
 
                // Avoid fatals if close() was called
@@ -3054,10 +3353,10 @@ abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAware
                                        "$fname: No transaction to commit, something got out of sync." );
                                return; // nothing to do
                        } elseif ( $this->trxAutomatic ) {
-                               // @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
+                               throw new DBUnexpectedError(
+                                       $this,
+                                       "$fname: Expected mass commit of all peer transactions (DBO_TRX set)."
+                               );
                        }
                }
 
@@ -3096,47 +3395,50 @@ abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAware
        }
 
        final public function rollback( $fname = __METHOD__, $flush = '' ) {
-               if ( $flush === self::FLUSHING_INTERNAL || $flush === self::FLUSHING_ALL_PEERS ) {
-                       if ( !$this->trxLevel ) {
-                               return; // nothing to do
-                       }
-               } else {
-                       if ( !$this->trxLevel ) {
-                               $this->queryLogger->error(
-                                       "$fname: No transaction to rollback, something got out of sync." );
-                               return; // nothing to do
-                       } elseif ( $this->getFlag( self::DBO_TRX ) ) {
+               $trxActive = $this->trxLevel;
+
+               if ( $flush !== self::FLUSHING_INTERNAL && $flush !== self::FLUSHING_ALL_PEERS ) {
+                       if ( $this->getFlag( self::DBO_TRX ) ) {
                                throw new DBUnexpectedError(
                                        $this,
-                                       "$fname: Expected mass rollback of all peer databases (DBO_TRX set)."
+                                       "$fname: Expected mass rollback of all peer transactions (DBO_TRX set)."
                                );
                        }
                }
 
-               // Avoid fatals if close() was called
-               $this->assertOpen();
+               if ( $trxActive ) {
+                       // Avoid fatals if close() was called
+                       $this->assertOpen();
 
-               $this->doRollback( $fname );
-               $this->trxAtomicLevels = [];
-               if ( $this->trxDoneWrites ) {
-                       $this->trxProfiler->transactionWritingOut(
-                               $this->server,
-                               $this->dbName,
-                               $this->trxShortId
-                       );
+                       $this->doRollback( $fname );
+                       $this->trxAtomicLevels = [];
+                       if ( $this->trxDoneWrites ) {
+                               $this->trxProfiler->transactionWritingOut(
+                                       $this->server,
+                                       $this->dbName,
+                                       $this->trxShortId
+                               );
+                       }
                }
 
-               $this->trxIdleCallbacks = []; // clear
-               $this->trxPreCommitCallbacks = []; // clear
-               try {
-                       $this->runOnTransactionIdleCallbacks( self::TRIGGER_ROLLBACK );
-               } catch ( Exception $e ) {
-                       // already logged; finish and let LoadBalancer move on during mass-rollback
-               }
-               try {
-                       $this->runTransactionListenerCallbacks( self::TRIGGER_ROLLBACK );
-               } catch ( Exception $e ) {
-                       // already logged; let LoadBalancer move on during mass-rollback
+               // Clear any commit-dependant callbacks. They might even be present
+               // only due to transaction rounds, with no SQL transaction being active
+               $this->trxIdleCallbacks = [];
+               $this->trxPreCommitCallbacks = [];
+
+               if ( $trxActive ) {
+                       try {
+                               $this->runOnTransactionIdleCallbacks( self::TRIGGER_ROLLBACK );
+                       } catch ( Exception $e ) {
+                               // already logged; finish and let LoadBalancer move on during mass-rollback
+                       }
+                       try {
+                               $this->runTransactionListenerCallbacks( self::TRIGGER_ROLLBACK );
+                       } catch ( Exception $e ) {
+                               // already logged; let LoadBalancer move on during mass-rollback
+                       }
+
+                       $this->affectedRowCount = 0; // for the sake of consistency
                }
        }
 
@@ -3735,12 +4037,8 @@ abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAware
                $this->tableAliases = $aliases;
        }
 
-       /**
-        * @return bool Whether a DB user is required to access the DB
-        * @since 1.28
-        */
-       protected function requiresDatabaseUser() {
-               return true;
+       public function setIndexAliases( array $aliases ) {
+               $this->indexAliases = $aliases;
        }
 
        /**
@@ -3750,7 +4048,7 @@ abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAware
         * This catches broken callers than catch and ignore disconnection exceptions.
         * Unlike checking isOpen(), this is safe to call inside of open().
         *
-        * @return resource|object
+        * @return mixed
         * @throws DBUnexpectedError
         * @since 1.26
         */