includes/db/loadbalancer/ILoadBalancer.php

   1 <?php
   2 /**
   3  * Database load balancing interface
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  * @ingroup Database
  22  * @author Aaron Schulz
  23  */
  24
  25 /**
  26  * Interface for database load balancing object that manages IDatabase handles
  27  *
  28  * @todo: loosen up DB classes from MWException
  29  * @since 1.28
  30  * @ingroup Database
  31  */
  32 interface ILoadBalancer {
  33         /**
  34          * @param array $params Array with keys:
  35          *  - servers : Required. Array of server info structures.
  36          *  - loadMonitor : Name of a class used to fetch server lag and load.
  37          *  - readOnlyReason : Reason the master DB is read-only if so [optional]
  38          *  - waitTimeout : Maximum time to wait for replicas for consistency [optional]
  39          *  - srvCache : BagOStuff object [optional]
  40          *  - wanCache : WANObjectCache object [optional]
  41          * @throws MWException
  42          */
  43         public function __construct( array $params );
  44
  45         /**
  46          * Get the index of the reader connection, which may be a replica DB
  47          * This takes into account load ratios and lag times. It should
  48          * always return a consistent index during a given invocation
  49          *
  50          * Side effect: opens connections to databases
  51          * @param string|bool $group Query group, or false for the generic reader
  52          * @param string|bool $wiki Wiki ID, or false for the current wiki
  53          * @throws MWException
  54          * @return bool|int|string
  55          */
  56         public function getReaderIndex( $group = false, $wiki = false );
  57
  58         /**
  59          * Set the master wait position
  60          * If a DB_REPLICA connection has been opened already, waits
  61          * Otherwise sets a variable telling it to wait if such a connection is opened
  62          * @param DBMasterPos $pos
  63          */
  64         public function waitFor( $pos );
  65
  66         /**
  67          * Set the master wait position and wait for a "generic" replica DB to catch up to it
  68          *
  69          * This can be used a faster proxy for waitForAll()
  70          *
  71          * @param DBMasterPos $pos
  72          * @param int $timeout Max seconds to wait; default is mWaitTimeout
  73          * @return bool Success (able to connect and no timeouts reached)
  74          */
  75         public function waitForOne( $pos, $timeout = null );
  76
  77         /**
  78          * Set the master wait position and wait for ALL replica DBs to catch up to it
  79          * @param DBMasterPos $pos
  80          * @param int $timeout Max seconds to wait; default is mWaitTimeout
  81          * @return bool Success (able to connect and no timeouts reached)
  82          */
  83         public function waitForAll( $pos, $timeout = null );
  84
  85         /**
  86          * Get any open connection to a given server index, local or foreign
  87          * Returns false if there is no connection open
  88          *
  89          * @param int $i Server index
  90          * @return IDatabase|bool False on failure
  91          */
  92         public function getAnyOpenConnection( $i );
  93
  94         /**
  95          * Get a connection by index
  96          * This is the main entry point for this class.
  97          *
  98          * @param int $i Server index
  99          * @param array|string|bool $groups Query group(s), or false for the generic reader
 100          * @param string|bool $wiki Wiki ID, or false for the current wiki
 101          *
 102          * @throws MWException
 103          * @return IDatabase
 104          */
 105         public function getConnection( $i, $groups = [], $wiki = false );
 106
 107         /**
 108          * Mark a foreign connection as being available for reuse under a different
 109          * DB name or prefix. This mechanism is reference-counted, and must be called
 110          * the same number of times as getConnection() to work.
 111          *
 112          * @param IDatabase $conn
 113          * @throws MWException
 114          */
 115         public function reuseConnection( $conn );
 116
 117         /**
 118          * Get a database connection handle reference
 119          *
 120          * The handle's methods wrap simply wrap those of a IDatabase handle
 121          *
 122          * @see LoadBalancer::getConnection() for parameter information
 123          *
 124          * @param int $db
 125          * @param array|string|bool $groups Query group(s), or false for the generic reader
 126          * @param string|bool $wiki Wiki ID, or false for the current wiki
 127          * @return DBConnRef
 128          */
 129         public function getConnectionRef( $db, $groups = [], $wiki = false );
 130
 131         /**
 132          * Get a database connection handle reference without connecting yet
 133          *
 134          * The handle's methods wrap simply wrap those of a IDatabase handle
 135          *
 136          * @see LoadBalancer::getConnection() for parameter information
 137          *
 138          * @param int $db
 139          * @param array|string|bool $groups Query group(s), or false for the generic reader
 140          * @param string|bool $wiki Wiki ID, or false for the current wiki
 141          * @return DBConnRef
 142          */
 143         public function getLazyConnectionRef( $db, $groups = [], $wiki = false );
 144
 145         /**
 146          * Open a connection to the server given by the specified index
 147          * Index must be an actual index into the array.
 148          * If the server is already open, returns it.
 149          *
 150          * On error, returns false, and the connection which caused the
 151          * error will be available via $this->mErrorConnection.
 152          *
 153          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 154          *
 155          * @param int $i Server index
 156          * @param string|bool $wiki Wiki ID, or false for the current wiki
 157          * @return IDatabase|bool Returns false on errors
 158          */
 159         public function openConnection( $i, $wiki = false );
 160
 161         /**
 162          * @return int
 163          */
 164         public function getWriterIndex();
 165
 166         /**
 167          * Returns true if the specified index is a valid server index
 168          *
 169          * @param string $i
 170          * @return bool
 171          */
 172         public function haveIndex( $i );
 173
 174         /**
 175          * Returns true if the specified index is valid and has non-zero load
 176          *
 177          * @param string $i
 178          * @return bool
 179          */
 180         public function isNonZeroLoad( $i );
 181
 182         /**
 183          * Get the number of defined servers (not the number of open connections)
 184          *
 185          * @return int
 186          */
 187         public function getServerCount();
 188
 189         /**
 190          * Get the host name or IP address of the server with the specified index
 191          * Prefer a readable name if available.
 192          * @param string $i
 193          * @return string
 194          */
 195         public function getServerName( $i );
 196
 197         /**
 198          * Return the server info structure for a given index, or false if the index is invalid.
 199          * @param int $i
 200          * @return array|bool
 201          */
 202         public function getServerInfo( $i );
 203
 204         /**
 205          * Sets the server info structure for the given index. Entry at index $i
 206          * is created if it doesn't exist
 207          * @param int $i
 208          * @param array $serverInfo
 209          */
 210         public function setServerInfo( $i, array $serverInfo );
 211
 212         /**
 213          * Get the current master position for chronology control purposes
 214          * @return DBMasterPos|bool Returns false if not applicable
 215          */
 216         public function getMasterPos();
 217
 218         /**
 219          * Disable this load balancer. All connections are closed, and any attempt to
 220          * open a new connection will result in a DBAccessError.
 221          */
 222         public function disable();
 223
 224         /**
 225          * Close all open connections
 226          */
 227         public function closeAll();
 228
 229         /**
 230          * Close a connection
 231          *
 232          * Using this function makes sure the LoadBalancer knows the connection is closed.
 233          * If you use $conn->close() directly, the load balancer won't update its state.
 234          *
 235          * @param IDatabase $conn
 236          */
 237         public function closeConnection( IDatabase $conn );
 238
 239         /**
 240          * Commit transactions on all open connections
 241          * @param string $fname Caller name
 242          * @throws DBExpectedError
 243          */
 244         public function commitAll( $fname = __METHOD__ );
 245
 246         /**
 247          * Perform all pre-commit callbacks that remain part of the atomic transactions
 248          * and disable any post-commit callbacks until runMasterPostTrxCallbacks()
 249          *
 250          * Use this only for mutli-database commits
 251          */
 252         public function finalizeMasterChanges();
 253
 254         /**
 255          * Perform all pre-commit checks for things like replication safety
 256          *
 257          * Use this only for mutli-database commits
 258          *
 259          * @param array $options Includes:
 260          *   - maxWriteDuration : max write query duration time in seconds
 261          * @throws DBTransactionError
 262          */
 263         public function approveMasterChanges( array $options );
 264
 265         /**
 266          * Flush any master transaction snapshots and set DBO_TRX (if DBO_DEFAULT is set)
 267          *
 268          * The DBO_TRX setting will be reverted to the default in each of these methods:
 269          *   - commitMasterChanges()
 270          *   - rollbackMasterChanges()
 271          *   - commitAll()
 272          * This allows for custom transaction rounds from any outer transaction scope.
 273          *
 274          * @param string $fname
 275          * @throws DBExpectedError
 276          */
 277         public function beginMasterChanges( $fname = __METHOD__ );
 278
 279         /**
 280          * Issue COMMIT on all master connections where writes where done
 281          * @param string $fname Caller name
 282          * @throws DBExpectedError
 283          */
 284         public function commitMasterChanges( $fname = __METHOD__ );
 285
 286         /**
 287          * Issue all pending post-COMMIT/ROLLBACK callbacks
 288          *
 289          * Use this only for mutli-database commits
 290          *
 291          * @param integer $type IDatabase::TRIGGER_* constant
 292          * @return Exception|null The first exception or null if there were none
 293          */
 294         public function runMasterPostTrxCallbacks( $type );
 295
 296         /**
 297          * Issue ROLLBACK only on master, only if queries were done on connection
 298          * @param string $fname Caller name
 299          * @throws DBExpectedError
 300          */
 301         public function rollbackMasterChanges( $fname = __METHOD__ );
 302
 303         /**
 304          * Suppress all pending post-COMMIT/ROLLBACK callbacks
 305          *
 306          * Use this only for mutli-database commits
 307          *
 308          * @return Exception|null The first exception or null if there were none
 309          */
 310         public function suppressTransactionEndCallbacks();
 311
 312         /**
 313          * Commit all replica DB transactions so as to flush any REPEATABLE-READ or SSI snapshot
 314          *
 315          * @param string $fname Caller name
 316          */
 317         public function flushReplicaSnapshots( $fname = __METHOD__ );
 318
 319         /**
 320          * @return bool Whether a master connection is already open
 321          */
 322         public function hasMasterConnection();
 323
 324         /**
 325          * Determine if there are pending changes in a transaction by this thread
 326          * @return bool
 327          */
 328         public function hasMasterChanges();
 329
 330         /**
 331          * Get the timestamp of the latest write query done by this thread
 332          * @return float|bool UNIX timestamp or false
 333          */
 334         public function lastMasterChangeTimestamp();
 335
 336         /**
 337          * Check if this load balancer object had any recent or still
 338          * pending writes issued against it by this PHP thread
 339          *
 340          * @param float $age How many seconds ago is "recent" [defaults to mWaitTimeout]
 341          * @return bool
 342          */
 343         public function hasOrMadeRecentMasterChanges( $age = null );
 344
 345         /**
 346          * Get the list of callers that have pending master changes
 347          *
 348          * @return string[] List of method names
 349          */
 350         public function pendingMasterChangeCallers();
 351
 352         /**
 353          * @note This method will trigger a DB connection if not yet done
 354          * @param string|bool $wiki Wiki ID, or false for the current wiki
 355          * @return bool Whether the generic connection for reads is highly "lagged"
 356          */
 357         public function getLaggedReplicaMode( $wiki = false );
 358
 359         /**
 360          * @note This method will never cause a new DB connection
 361          * @return bool Whether any generic connection used for reads was highly "lagged"
 362          */
 363         public function laggedReplicaUsed();
 364
 365         /**
 366          * @note This method may trigger a DB connection if not yet done
 367          * @param string|bool $wiki Wiki ID, or false for the current wiki
 368          * @param IDatabase|null DB master connection; used to avoid loops [optional]
 369          * @return string|bool Reason the master is read-only or false if it is not
 370          */
 371         public function getReadOnlyReason( $wiki = false, IDatabase $conn = null );
 372
 373         /**
 374          * Disables/enables lag checks
 375          * @param null|bool $mode
 376          * @return bool
 377          */
 378         public function allowLagged( $mode = null );
 379
 380         /**
 381          * @return bool
 382          */
 383         public function pingAll();
 384
 385         /**
 386          * Call a function with each open connection object
 387          * @param callable $callback
 388          * @param array $params
 389          */
 390         public function forEachOpenConnection( $callback, array $params = [] );
 391
 392         /**
 393          * Call a function with each open connection object to a master
 394          * @param callable $callback
 395          * @param array $params
 396          */
 397         public function forEachOpenMasterConnection( $callback, array $params = [] );
 398
 399         /**
 400          * Call a function with each open replica DB connection object
 401          * @param callable $callback
 402          * @param array $params
 403          */
 404         public function forEachOpenReplicaConnection( $callback, array $params = [] );
 405
 406         /**
 407          * Get the hostname and lag time of the most-lagged replica DB
 408          *
 409          * This is useful for maintenance scripts that need to throttle their updates.
 410          * May attempt to open connections to replica DBs on the default DB. If there is
 411          * no lag, the maximum lag will be reported as -1.
 412          *
 413          * @param bool|string $wiki Wiki ID, or false for the default database
 414          * @return array ( host, max lag, index of max lagged host )
 415          */
 416         public function getMaxLag( $wiki = false );
 417
 418         /**
 419          * Get an estimate of replication lag (in seconds) for each server
 420          *
 421          * Results are cached for a short time in memcached/process cache
 422          *
 423          * Values may be "false" if replication is too broken to estimate
 424          *
 425          * @param string|bool $wiki
 426          * @return int[] Map of (server index => float|int|bool)
 427          */
 428         public function getLagTimes( $wiki = false );
 429
 430         /**
 431          * Get the lag in seconds for a given connection, or zero if this load
 432          * balancer does not have replication enabled.
 433          *
 434          * This should be used in preference to Database::getLag() in cases where
 435          * replication may not be in use, since there is no way to determine if
 436          * replication is in use at the connection level without running
 437          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
 438          * function instead of Database::getLag() avoids a fatal error in this
 439          * case on many installations.
 440          *
 441          * @param IDatabase $conn
 442          * @return int|bool Returns false on error
 443          */
 444         public function safeGetLag( IDatabase $conn );
 445
 446         /**
 447          * Wait for a replica DB to reach a specified master position
 448          *
 449          * This will connect to the master to get an accurate position if $pos is not given
 450          *
 451          * @param IDatabase $conn Replica DB
 452          * @param DBMasterPos|bool $pos Master position; default: current position
 453          * @param integer|null $timeout Timeout in seconds [optional]
 454          * @return bool Success
 455          */
 456         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = null );
 457
 458         /**
 459          * Clear the cache for slag lag delay times
 460          *
 461          * This is only used for testing
 462          */
 463         public function clearLagTimeCache();
 464
 465         /**
 466          * Set a callback via IDatabase::setTransactionListener() on
 467          * all current and future master connections of this load balancer
 468          *
 469          * @param string $name Callback name
 470          * @param callable|null $callback
 471          */
 472         public function setTransactionListener( $name, callable $callback = null );
 473 }