includes/libs/rdbms/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  * @since 1.28
  29  * @ingroup Database
  30  */
  31 interface ILoadBalancer {
  32         /**
  33          * @param array $params Array with keys:
  34          *  - servers : Required. Array of server info structures.
  35          *  - loadMonitor : Name of a class used to fetch server lag and load.
  36          *  - readOnlyReason : Reason the master DB is read-only if so [optional]
  37          *  - waitTimeout : Maximum time to wait for replicas for consistency [optional]
  38          *  - srvCache : BagOStuff object for server cache [optional]
  39          *  - memCache : BagOStuff object for cluster memory cache [optional]
  40          *  - wanCache : WANObjectCache object [optional]
  41          *  - hostname : the name of the current server [optional]
  42          * @throws InvalidArgumentException
  43          */
  44         public function __construct( array $params );
  45
  46         /**
  47          * Get the index of the reader connection, which may be a replica DB
  48          * This takes into account load ratios and lag times. It should
  49          * always return a consistent index during a given invocation
  50          *
  51          * Side effect: opens connections to databases
  52          * @param string|bool $group Query group, or false for the generic reader
  53          * @param string|bool $wiki Wiki ID, or false for the current wiki
  54          * @throws DBError
  55          * @return bool|int|string
  56          */
  57         public function getReaderIndex( $group = false, $wiki = false );
  58
  59         /**
  60          * Set the master wait position
  61          * If a DB_REPLICA connection has been opened already, waits
  62          * Otherwise sets a variable telling it to wait if such a connection is opened
  63          * @param DBMasterPos $pos
  64          */
  65         public function waitFor( $pos );
  66
  67         /**
  68          * Set the master wait position and wait for a "generic" replica DB to catch up to it
  69          *
  70          * This can be used a faster proxy for waitForAll()
  71          *
  72          * @param DBMasterPos $pos
  73          * @param int $timeout Max seconds to wait; default is mWaitTimeout
  74          * @return bool Success (able to connect and no timeouts reached)
  75          */
  76         public function waitForOne( $pos, $timeout = null );
  77
  78         /**
  79          * Set the master wait position and wait for ALL replica DBs to catch up to it
  80          * @param DBMasterPos $pos
  81          * @param int $timeout Max seconds to wait; default is mWaitTimeout
  82          * @return bool Success (able to connect and no timeouts reached)
  83          */
  84         public function waitForAll( $pos, $timeout = null );
  85
  86         /**
  87          * Get any open connection to a given server index, local or foreign
  88          * Returns false if there is no connection open
  89          *
  90          * @param int $i Server index
  91          * @return IDatabase|bool False on failure
  92          */
  93         public function getAnyOpenConnection( $i );
  94
  95         /**
  96          * Get a connection by index
  97          * This is the main entry point for this class.
  98          *
  99          * @param int $i Server index
 100          * @param array|string|bool $groups Query group(s), or false for the generic reader
 101          * @param string|bool $wiki Wiki ID, or false for the current wiki
 102          *
 103          * @throws DBError
 104          * @return IDatabase
 105          */
 106         public function getConnection( $i, $groups = [], $wiki = false );
 107
 108         /**
 109          * Mark a foreign connection as being available for reuse under a different
 110          * DB name or prefix. This mechanism is reference-counted, and must be called
 111          * the same number of times as getConnection() to work.
 112          *
 113          * @param IDatabase $conn
 114          * @throws InvalidArgumentException
 115          */
 116         public function reuseConnection( $conn );
 117
 118         /**
 119          * Get a database connection handle reference
 120          *
 121          * The handle's methods wrap simply wrap those of a IDatabase handle
 122          *
 123          * @see LoadBalancer::getConnection() for parameter information
 124          *
 125          * @param int $db
 126          * @param array|string|bool $groups Query group(s), or false for the generic reader
 127          * @param string|bool $wiki Wiki ID, or false for the current wiki
 128          * @return DBConnRef
 129          */
 130         public function getConnectionRef( $db, $groups = [], $wiki = false );
 131
 132         /**
 133          * Get a database connection handle reference without connecting yet
 134          *
 135          * The handle's methods wrap simply wrap those of a IDatabase handle
 136          *
 137          * @see LoadBalancer::getConnection() for parameter information
 138          *
 139          * @param int $db
 140          * @param array|string|bool $groups Query group(s), or false for the generic reader
 141          * @param string|bool $wiki Wiki ID, or false for the current wiki
 142          * @return DBConnRef
 143          */
 144         public function getLazyConnectionRef( $db, $groups = [], $wiki = false );
 145
 146         /**
 147          * Open a connection to the server given by the specified index
 148          * Index must be an actual index into the array.
 149          * If the server is already open, returns it.
 150          *
 151          * On error, returns false, and the connection which caused the
 152          * error will be available via $this->mErrorConnection.
 153          *
 154          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 155          *
 156          * @param int $i Server index
 157          * @param string|bool $wiki Wiki ID, or false for the current wiki
 158          * @return IDatabase|bool Returns false on errors
 159          */
 160         public function openConnection( $i, $wiki = false );
 161
 162         /**
 163          * @return int
 164          */
 165         public function getWriterIndex();
 166
 167         /**
 168          * Returns true if the specified index is a valid server index
 169          *
 170          * @param string $i
 171          * @return bool
 172          */
 173         public function haveIndex( $i );
 174
 175         /**
 176          * Returns true if the specified index is valid and has non-zero load
 177          *
 178          * @param string $i
 179          * @return bool
 180          */
 181         public function isNonZeroLoad( $i );
 182
 183         /**
 184          * Get the number of defined servers (not the number of open connections)
 185          *
 186          * @return int
 187          */
 188         public function getServerCount();
 189
 190         /**
 191          * Get the host name or IP address of the server with the specified index
 192          * Prefer a readable name if available.
 193          * @param string $i
 194          * @return string
 195          */
 196         public function getServerName( $i );
 197
 198         /**
 199          * Return the server info structure for a given index, or false if the index is invalid.
 200          * @param int $i
 201          * @return array|bool
 202          */
 203         public function getServerInfo( $i );
 204
 205         /**
 206          * Sets the server info structure for the given index. Entry at index $i
 207          * is created if it doesn't exist
 208          * @param int $i
 209          * @param array $serverInfo
 210          */
 211         public function setServerInfo( $i, array $serverInfo );
 212
 213         /**
 214          * Get the current master position for chronology control purposes
 215          * @return DBMasterPos|bool Returns false if not applicable
 216          */
 217         public function getMasterPos();
 218
 219         /**
 220          * Disable this load balancer. All connections are closed, and any attempt to
 221          * open a new connection will result in a DBAccessError.
 222          */
 223         public function disable();
 224
 225         /**
 226          * Close all open connections
 227          */
 228         public function closeAll();
 229
 230         /**
 231          * Close a connection
 232          *
 233          * Using this function makes sure the LoadBalancer knows the connection is closed.
 234          * If you use $conn->close() directly, the load balancer won't update its state.
 235          *
 236          * @param IDatabase $conn
 237          */
 238         public function closeConnection( IDatabase $conn );
 239
 240         /**
 241          * Commit transactions on all open connections
 242          * @param string $fname Caller name
 243          * @throws DBExpectedError
 244          */
 245         public function commitAll( $fname = __METHOD__ );
 246
 247         /**
 248          * Perform all pre-commit callbacks that remain part of the atomic transactions
 249          * and disable any post-commit callbacks until runMasterPostTrxCallbacks()
 250          *
 251          * Use this only for mutli-database commits
 252          */
 253         public function finalizeMasterChanges();
 254
 255         /**
 256          * Perform all pre-commit checks for things like replication safety
 257          *
 258          * Use this only for mutli-database commits
 259          *
 260          * @param array $options Includes:
 261          *   - maxWriteDuration : max write query duration time in seconds
 262          * @throws DBTransactionError
 263          */
 264         public function approveMasterChanges( array $options );
 265
 266         /**
 267          * Flush any master transaction snapshots and set DBO_TRX (if DBO_DEFAULT is set)
 268          *
 269          * The DBO_TRX setting will be reverted to the default in each of these methods:
 270          *   - commitMasterChanges()
 271          *   - rollbackMasterChanges()
 272          *   - commitAll()
 273          * This allows for custom transaction rounds from any outer transaction scope.
 274          *
 275          * @param string $fname
 276          * @throws DBExpectedError
 277          */
 278         public function beginMasterChanges( $fname = __METHOD__ );
 279
 280         /**
 281          * Issue COMMIT on all master connections where writes where done
 282          * @param string $fname Caller name
 283          * @throws DBExpectedError
 284          */
 285         public function commitMasterChanges( $fname = __METHOD__ );
 286
 287         /**
 288          * Issue all pending post-COMMIT/ROLLBACK callbacks
 289          *
 290          * Use this only for mutli-database commits
 291          *
 292          * @param integer $type IDatabase::TRIGGER_* constant
 293          * @return Exception|null The first exception or null if there were none
 294          */
 295         public function runMasterPostTrxCallbacks( $type );
 296
 297         /**
 298          * Issue ROLLBACK only on master, only if queries were done on connection
 299          * @param string $fname Caller name
 300          * @throws DBExpectedError
 301          */
 302         public function rollbackMasterChanges( $fname = __METHOD__ );
 303
 304         /**
 305          * Suppress all pending post-COMMIT/ROLLBACK callbacks
 306          *
 307          * Use this only for mutli-database commits
 308          *
 309          * @return Exception|null The first exception or null if there were none
 310          */
 311         public function suppressTransactionEndCallbacks();
 312
 313         /**
 314          * Commit all replica DB transactions so as to flush any REPEATABLE-READ or SSI snapshot
 315          *
 316          * @param string $fname Caller name
 317          */
 318         public function flushReplicaSnapshots( $fname = __METHOD__ );
 319
 320         /**
 321          * @return bool Whether a master connection is already open
 322          */
 323         public function hasMasterConnection();
 324
 325         /**
 326          * Determine if there are pending changes in a transaction by this thread
 327          * @return bool
 328          */
 329         public function hasMasterChanges();
 330
 331         /**
 332          * Get the timestamp of the latest write query done by this thread
 333          * @return float|bool UNIX timestamp or false
 334          */
 335         public function lastMasterChangeTimestamp();
 336
 337         /**
 338          * Check if this load balancer object had any recent or still
 339          * pending writes issued against it by this PHP thread
 340          *
 341          * @param float $age How many seconds ago is "recent" [defaults to mWaitTimeout]
 342          * @return bool
 343          */
 344         public function hasOrMadeRecentMasterChanges( $age = null );
 345
 346         /**
 347          * Get the list of callers that have pending master changes
 348          *
 349          * @return string[] List of method names
 350          */
 351         public function pendingMasterChangeCallers();
 352
 353         /**
 354          * @note This method will trigger a DB connection if not yet done
 355          * @param string|bool $wiki Wiki ID, or false for the current wiki
 356          * @return bool Whether the generic connection for reads is highly "lagged"
 357          */
 358         public function getLaggedReplicaMode( $wiki = false );
 359
 360         /**
 361          * @note This method will never cause a new DB connection
 362          * @return bool Whether any generic connection used for reads was highly "lagged"
 363          */
 364         public function laggedReplicaUsed();
 365
 366         /**
 367          * @note This method may trigger a DB connection if not yet done
 368          * @param string|bool $wiki Wiki ID, or false for the current wiki
 369          * @param IDatabase|null DB master connection; used to avoid loops [optional]
 370          * @return string|bool Reason the master is read-only or false if it is not
 371          */
 372         public function getReadOnlyReason( $wiki = false, IDatabase $conn = null );
 373
 374         /**
 375          * Disables/enables lag checks
 376          * @param null|bool $mode
 377          * @return bool
 378          */
 379         public function allowLagged( $mode = null );
 380
 381         /**
 382          * @return bool
 383          */
 384         public function pingAll();
 385
 386         /**
 387          * Call a function with each open connection object
 388          * @param callable $callback
 389          * @param array $params
 390          */
 391         public function forEachOpenConnection( $callback, array $params = [] );
 392
 393         /**
 394          * Call a function with each open connection object to a master
 395          * @param callable $callback
 396          * @param array $params
 397          */
 398         public function forEachOpenMasterConnection( $callback, array $params = [] );
 399
 400         /**
 401          * Call a function with each open replica DB connection object
 402          * @param callable $callback
 403          * @param array $params
 404          */
 405         public function forEachOpenReplicaConnection( $callback, array $params = [] );
 406
 407         /**
 408          * Get the hostname and lag time of the most-lagged replica DB
 409          *
 410          * This is useful for maintenance scripts that need to throttle their updates.
 411          * May attempt to open connections to replica DBs on the default DB. If there is
 412          * no lag, the maximum lag will be reported as -1.
 413          *
 414          * @param bool|string $wiki Wiki ID, or false for the default database
 415          * @return array ( host, max lag, index of max lagged host )
 416          */
 417         public function getMaxLag( $wiki = false );
 418
 419         /**
 420          * Get an estimate of replication lag (in seconds) for each server
 421          *
 422          * Results are cached for a short time in memcached/process cache
 423          *
 424          * Values may be "false" if replication is too broken to estimate
 425          *
 426          * @param string|bool $wiki
 427          * @return int[] Map of (server index => float|int|bool)
 428          */
 429         public function getLagTimes( $wiki = false );
 430
 431         /**
 432          * Get the lag in seconds for a given connection, or zero if this load
 433          * balancer does not have replication enabled.
 434          *
 435          * This should be used in preference to Database::getLag() in cases where
 436          * replication may not be in use, since there is no way to determine if
 437          * replication is in use at the connection level without running
 438          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
 439          * function instead of Database::getLag() avoids a fatal error in this
 440          * case on many installations.
 441          *
 442          * @param IDatabase $conn
 443          * @return int|bool Returns false on error
 444          */
 445         public function safeGetLag( IDatabase $conn );
 446
 447         /**
 448          * Wait for a replica DB to reach a specified master position
 449          *
 450          * This will connect to the master to get an accurate position if $pos is not given
 451          *
 452          * @param IDatabase $conn Replica DB
 453          * @param DBMasterPos|bool $pos Master position; default: current position
 454          * @param integer|null $timeout Timeout in seconds [optional]
 455          * @return bool Success
 456          */
 457         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = null );
 458
 459         /**
 460          * Clear the cache for slag lag delay times
 461          *
 462          * This is only used for testing
 463          */
 464         public function clearLagTimeCache();
 465
 466         /**
 467          * Set a callback via IDatabase::setTransactionListener() on
 468          * all current and future master connections of this load balancer
 469          *
 470          * @param string $name Callback name
 471          * @param callable|null $callback
 472          */
 473         public function setTransactionListener( $name, callable $callback = null );
 474 }