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