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  */
  23 namespace Wikimedia\Rdbms;
  24
  25 use Exception;
  26 use InvalidArgumentException;
  27
  28 /**
  29  * Database cluster connection, tracking, load balancing, and transaction manager interface
  30  *
  31  * A "cluster" is considered to be one master database and zero or more replica databases.
  32  * Typically, the replica DBs replicate from the master asynchronously. The first node in the
  33  * "servers" configuration array is always considered the "master". However, this class can still
  34  * be used when all or some of the "replica" DBs are multi-master peers of the master or even
  35  * when all the DBs are non-replicating clones of each other holding read-only data. Thus, the
  36  * role of "master" is in some cases merely nominal.
  37  *
  38  * By default, each DB server uses DBO_DEFAULT for its 'flags' setting, unless explicitly set
  39  * otherwise in configuration. DBO_DEFAULT behavior depends on whether 'cliMode' is set:
  40  *   - In CLI mode, the flag has no effect with regards to LoadBalancer.
  41  *   - In non-CLI mode, the flag causes implicit transactions to be used; the first query on
  42  *     a database starts a transaction on that database. The transactions are meant to remain
  43  *     pending until either commitMasterChanges() or rollbackMasterChanges() is called. The
  44  *     application must have some point where it calls commitMasterChanges() near the end of
  45  *     the PHP request.
  46  * Every iteration of beginMasterChanges()/commitMasterChanges() is called a "transaction round".
  47  * Rounds are useful on the master DB connections because they make single-DB (and by and large
  48  * multi-DB) updates in web requests all-or-nothing. Also, transactions on replica DBs are useful
  49  * when REPEATABLE-READ or SERIALIZABLE isolation is used because all foriegn keys and constraints
  50  * hold across separate queries in the DB transaction since the data appears within a consistent
  51  * point-in-time snapshot.
  52  *
  53  * The typical caller will use LoadBalancer::getConnection( DB_* ) to yield a live database
  54  * connection handle. The choice of which DB server to use is based on pre-defined loads for
  55  * weighted random selection, adjustments thereof by LoadMonitor, and the amount of replication
  56  * lag on each DB server. Lag checks might cause problems in certain setups, so they should be
  57  * tuned in the server configuration maps as follows:
  58  *   - Master + N Replica(s): set 'max lag' to an appropriate threshold for avoiding any database
  59  *      lagged by this much or more. If all DBs are this lagged, then the load balancer considers
  60  *      the cluster to be read-only.
  61  *   - Galera Cluster: Seconds_Behind_Master will be 0, so there probably is nothing to tune.
  62  *      Note that lag is still possible depending on how wsrep-sync-wait is set server-side.
  63  *   - Read-only archive clones: set 'is static' in the server configuration maps. This will
  64  *      treat all such DBs as having 0 lag.
  65  *   - SQL load balancing proxy: any proxy should handle lag checks on its own, so the 'max lag'
  66  *      parameter should probably be set to INF in the server configuration maps. This will make
  67  *      the load balancer ignore whatever it detects as the lag of the logical replica is (which
  68  *      would probably just randomly bounce around).
  69  *
  70  * If using a SQL proxy service, it would probably be best to have two proxy hosts for the
  71  * load balancer to talk to. One would be the 'host' of the master server entry and another for
  72  * the (logical) replica server entry. The proxy could map the load balancer's "replica" DB to
  73  * any number of physical replica DBs.
  74  *
  75  * @since 1.28
  76  * @ingroup Database
  77  */
  78 interface ILoadBalancer {
  79         /** @var int Request a replica DB connection */
  80         const DB_REPLICA = -1;
  81         /** @var int Request a master DB connection */
  82         const DB_MASTER = -2;
  83
  84         /** @var string Domain specifier when no specific database needs to be selected */
  85         const DOMAIN_ANY = '';
  86
  87         /** @var int DB handle should have DBO_TRX disabled and the caller will leave it as such */
  88         const CONN_TRX_AUTOCOMMIT = 1;
  89
  90         /** @var string Manager of ILoadBalancer instances is running post-commit callbacks */
  91         const STAGE_POSTCOMMIT_CALLBACKS = 'stage-postcommit-callbacks';
  92         /** @var string Manager of ILoadBalancer instances is running post-rollback callbacks */
  93         const STAGE_POSTROLLBACK_CALLBACKS = 'stage-postrollback-callbacks';
  94
  95         /**
  96          * Construct a manager of IDatabase connection objects
  97          *
  98          * @param array $params Parameter map with keys:
  99          *  - servers : Required. Array of server info structures.
 100          *  - localDomain: A DatabaseDomain or domain ID string.
 101          *  - loadMonitor : Name of a class used to fetch server lag and load.
 102          *  - readOnlyReason : Reason the master DB is read-only if so [optional]
 103          *  - waitTimeout : Maximum time to wait for replicas for consistency [optional]
 104          *  - maxLag: Avoid replica DB servers with more lag than this [optional]
 105          *  - srvCache : BagOStuff object for server cache [optional]
 106          *  - wanCache : WANObjectCache object [optional]
 107          *  - chronologyCallback: Callback to run before the first connection attempt [optional]
 108          *  - hostname : The name of the current server [optional]
 109          *  - cliMode: Whether the execution context is a CLI script. [optional]
 110          *  - profiler : Class name or instance with profileIn()/profileOut() methods. [optional]
 111          *  - trxProfiler: TransactionProfiler instance. [optional]
 112          *  - replLogger: PSR-3 logger instance. [optional]
 113          *  - connLogger: PSR-3 logger instance. [optional]
 114          *  - queryLogger: PSR-3 logger instance. [optional]
 115          *  - perfLogger: PSR-3 logger instance. [optional]
 116          *  - errorLogger : Callback that takes an Exception and logs it. [optional]
 117          *  - deprecationLogger: Callback to log a deprecation warning. [optional]
 118          *  - roundStage: STAGE_POSTCOMMIT_* class constant; for internal use [optional]
 119          * @throws InvalidArgumentException
 120          */
 121         public function __construct( array $params );
 122
 123         /**
 124          * Get the index of the reader connection, which may be a replica DB
 125          *
 126          * This takes into account load ratios and lag times. It should
 127          * always return a consistent index during a given invocation.
 128          *
 129          * Side effect: opens connections to databases
 130          * @param string|bool $group Query group, or false for the generic reader
 131          * @param string|bool $domain Domain ID, or false for the current domain
 132          * @throws DBError
 133          * @return bool|int|string
 134          */
 135         public function getReaderIndex( $group = false, $domain = false );
 136
 137         /**
 138          * Set the master wait position
 139          *
 140          * If a DB_REPLICA connection has been opened already, then wait immediately.
 141          * Otherwise sets a variable telling it to wait if such a connection is opened.
 142          *
 143          * This only applies to connections to the generic replica DB for this request.
 144          * If a timeout happens when waiting, then getLaggedReplicaMode()/laggedReplicaUsed()
 145          * will return true.
 146          *
 147          * @param DBMasterPos|bool $pos Master position or false
 148          */
 149         public function waitFor( $pos );
 150
 151         /**
 152          * Set the master wait position and wait for a "generic" replica DB to catch up to it
 153          *
 154          * This can be used a faster proxy for waitForAll()
 155          *
 156          * @param DBMasterPos|bool $pos Master position or false
 157          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 158          * @return bool Success (able to connect and no timeouts reached)
 159          */
 160         public function waitForOne( $pos, $timeout = null );
 161
 162         /**
 163          * Set the master wait position and wait for ALL replica DBs to catch up to it
 164          *
 165          * @param DBMasterPos|bool $pos Master position or false
 166          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 167          * @return bool Success (able to connect and no timeouts reached)
 168          */
 169         public function waitForAll( $pos, $timeout = null );
 170
 171         /**
 172          * Get any open connection to a given server index, local or foreign
 173          *
 174          * Use CONN_TRX_AUTOCOMMIT to only look for connections opened with that flag
 175          *
 176          * @param int $i Server index or DB_MASTER/DB_REPLICA
 177          * @param int $flags Bitfield of CONN_* class constants
 178          * @return Database|bool False if no such connection is open
 179          */
 180         public function getAnyOpenConnection( $i, $flags = 0 );
 181
 182         /**
 183          * Get a connection handle by server index
 184          *
 185          * The CONN_TRX_AUTOCOMMIT flag is ignored for databases with ATTR_DB_LEVEL_LOCKING
 186          * (e.g. sqlite) in order to avoid deadlocks. ILoadBalancer::getServerAttributes()
 187          * can be used to check such flags beforehand.
 188          *
 189          * If the caller uses $domain or sets CONN_TRX_AUTOCOMMIT in $flags, then it must also
 190          * call ILoadBalancer::reuseConnection() on the handle when finished using it.
 191          * In all other cases, this is not necessary, though not harmful either.
 192          *
 193          * @param int $i Server index (overrides $groups) or DB_MASTER/DB_REPLICA
 194          * @param array|string|bool $groups Query group(s), or false for the generic reader
 195          * @param string|bool $domain Domain ID, or false for the current domain
 196          * @param int $flags Bitfield of CONN_* class constants
 197          *
 198          * @note This method throws DBAccessError if ILoadBalancer::disable() was called
 199          *
 200          * @throws DBError
 201          * @return Database
 202          */
 203         public function getConnection( $i, $groups = [], $domain = false, $flags = 0 );
 204
 205         /**
 206          * Mark a foreign connection as being available for reuse under a different DB domain
 207          *
 208          * This mechanism is reference-counted, and must be called the same number of times
 209          * as getConnection() to work.
 210          *
 211          * @param IDatabase $conn
 212          * @throws InvalidArgumentException
 213          */
 214         public function reuseConnection( IDatabase $conn );
 215
 216         /**
 217          * Get a database connection handle reference
 218          *
 219          * The handle's methods simply wrap those of a Database handle
 220          *
 221          * The CONN_TRX_AUTOCOMMIT flag is ignored for databases with ATTR_DB_LEVEL_LOCKING
 222          * (e.g. sqlite) in order to avoid deadlocks. ILoadBalancer::getServerAttributes()
 223          * can be used to check such flags beforehand.
 224          *
 225          * @see ILoadBalancer::getConnection() for parameter information
 226          *
 227          * @param int $i Server index or DB_MASTER/DB_REPLICA
 228          * @param array|string|bool $groups Query group(s), or false for the generic reader
 229          * @param string|bool $domain Domain ID, or false for the current domain
 230          * @param int $flags Bitfield of CONN_* class constants (e.g. CONN_TRX_AUTOCOMMIT)
 231          * @return DBConnRef
 232          */
 233         public function getConnectionRef( $i, $groups = [], $domain = false, $flags = 0 );
 234
 235         /**
 236          * Get a database connection handle reference without connecting yet
 237          *
 238          * The handle's methods simply wrap those of a Database handle
 239          *
 240          * The CONN_TRX_AUTOCOMMIT flag is ignored for databases with ATTR_DB_LEVEL_LOCKING
 241          * (e.g. sqlite) in order to avoid deadlocks. ILoadBalancer::getServerAttributes()
 242          * can be used to check such flags beforehand.
 243          *
 244          * @see ILoadBalancer::getConnection() for parameter information
 245          *
 246          * @param int $i Server index or DB_MASTER/DB_REPLICA
 247          * @param array|string|bool $groups Query group(s), or false for the generic reader
 248          * @param string|bool $domain Domain ID, or false for the current domain
 249          * @param int $flags Bitfield of CONN_* class constants (e.g. CONN_TRX_AUTOCOMMIT)
 250          * @return DBConnRef
 251          */
 252         public function getLazyConnectionRef( $i, $groups = [], $domain = false, $flags = 0 );
 253
 254         /**
 255          * Get a maintenance database connection handle reference for migrations and schema changes
 256          *
 257          * The handle's methods simply wrap those of a Database handle
 258          *
 259          * The CONN_TRX_AUTOCOMMIT flag is ignored for databases with ATTR_DB_LEVEL_LOCKING
 260          * (e.g. sqlite) in order to avoid deadlocks. ILoadBalancer::getServerAttributes()
 261          * can be used to check such flags beforehand.
 262          *
 263          * @see ILoadBalancer::getConnection() for parameter information
 264          *
 265          * @param int $db Server index or DB_MASTER/DB_REPLICA
 266          * @param array|string|bool $groups Query group(s), or false for the generic reader
 267          * @param string|bool $domain Domain ID, or false for the current domain
 268          * @param int $flags Bitfield of CONN_* class constants (e.g. CONN_TRX_AUTOCOMMIT)
 269          * @return MaintainableDBConnRef
 270          */
 271         public function getMaintenanceConnectionRef( $db, $groups = [], $domain = false, $flags = 0 );
 272
 273         /**
 274          * Open a connection to the server given by the specified index
 275          *
 276          * The index must be an actual index into the array. If a connection to the server is
 277          * already open and not considered an "in use" foreign connection, this simply returns it.
 278          *
 279          * Avoid using CONN_TRX_AUTOCOMMIT for databases with ATTR_DB_LEVEL_LOCKING (e.g. sqlite) in
 280          * order to avoid deadlocks. ILoadBalancer::getServerAttributes() can be used to check
 281          * such flags beforehand.
 282          *
 283          * If the caller uses $domain or sets CONN_TRX_AUTOCOMMIT in $flags, then it must also
 284          * call ILoadBalancer::reuseConnection() on the handle when finished using it.
 285          * In all other cases, this is not necessary, though not harmful either.
 286          *
 287          * @note This method throws DBAccessError if ILoadBalancer::disable() was called
 288          *
 289          * @param int $i Server index (does not support DB_MASTER/DB_REPLICA)
 290          * @param string|bool $domain Domain ID, or false for the current domain
 291          * @param int $flags Bitfield of CONN_* class constants (e.g. CONN_TRX_AUTOCOMMIT)
 292          * @return Database|bool Returns false on errors
 293          * @throws DBAccessError
 294          */
 295         public function openConnection( $i, $domain = false, $flags = 0 );
 296
 297         /**
 298          * @return int
 299          */
 300         public function getWriterIndex();
 301
 302         /**
 303          * Returns true if the specified index is a valid server index
 304          *
 305          * @param int $i
 306          * @return bool
 307          */
 308         public function haveIndex( $i );
 309
 310         /**
 311          * Returns true if the specified index is valid and has non-zero load
 312          *
 313          * @param int $i
 314          * @return bool
 315          */
 316         public function isNonZeroLoad( $i );
 317
 318         /**
 319          * Get the number of defined servers (not the number of open connections)
 320          *
 321          * @return int
 322          */
 323         public function getServerCount();
 324
 325         /**
 326          * Get the host name or IP address of the server with the specified index
 327          *
 328          * @param int $i
 329          * @return string Readable name if available or IP/host otherwise
 330          */
 331         public function getServerName( $i );
 332
 333         /**
 334          * Return the server info structure for a given index, or false if the index is invalid.
 335          * @param int $i
 336          * @return array|bool
 337          */
 338         public function getServerInfo( $i );
 339
 340         /**
 341          * Get DB type of the server with the specified index
 342          *
 343          * @param int $i
 344          * @return string One of (mysql,postgres,sqlite,...) or "unknown" for bad indexes
 345          * @since 1.30
 346          */
 347         public function getServerType( $i );
 348
 349         /**
 350          * @param int $i Server index
 351          * @return array (Database::ATTRIBUTE_* constant => value) for all such constants
 352          * @since 1.31
 353          */
 354         public function getServerAttributes( $i );
 355
 356         /**
 357          * Get the current master position for chronology control purposes
 358          * @return DBMasterPos|bool Returns false if not applicable
 359          */
 360         public function getMasterPos();
 361
 362         /**
 363          * Disable this load balancer. All connections are closed, and any attempt to
 364          * open a new connection will result in a DBAccessError.
 365          */
 366         public function disable();
 367
 368         /**
 369          * Close all open connections
 370          */
 371         public function closeAll();
 372
 373         /**
 374          * Close a connection
 375          *
 376          * Using this function makes sure the LoadBalancer knows the connection is closed.
 377          * If you use $conn->close() directly, the load balancer won't update its state.
 378          *
 379          * @param IDatabase $conn
 380          */
 381         public function closeConnection( IDatabase $conn );
 382
 383         /**
 384          * Commit transactions on all open connections
 385          * @param string $fname Caller name
 386          * @throws DBExpectedError
 387          */
 388         public function commitAll( $fname = __METHOD__ );
 389
 390         /**
 391          * Run pre-commit callbacks and defer execution of post-commit callbacks
 392          *
 393          * Use this only for mutli-database commits
 394          *
 395          * @return int Number of pre-commit callbacks run (since 1.32)
 396          */
 397         public function finalizeMasterChanges();
 398
 399         /**
 400          * Perform all pre-commit checks for things like replication safety
 401          *
 402          * Use this only for mutli-database commits
 403          *
 404          * @param array $options Includes:
 405          *   - maxWriteDuration : max write query duration time in seconds
 406          * @throws DBTransactionError
 407          */
 408         public function approveMasterChanges( array $options );
 409
 410         /**
 411          * Flush any master transaction snapshots and set DBO_TRX (if DBO_DEFAULT is set)
 412          *
 413          * The DBO_TRX setting will be reverted to the default in each of these methods:
 414          *   - commitMasterChanges()
 415          *   - rollbackMasterChanges()
 416          *   - commitAll()
 417          * This allows for custom transaction rounds from any outer transaction scope.
 418          *
 419          * @param string $fname
 420          * @throws DBExpectedError
 421          */
 422         public function beginMasterChanges( $fname = __METHOD__ );
 423
 424         /**
 425          * Issue COMMIT on all master connections where writes where done
 426          * @param string $fname Caller name
 427          * @throws DBExpectedError
 428          */
 429         public function commitMasterChanges( $fname = __METHOD__ );
 430
 431         /**
 432          * Consume and run all pending post-COMMIT/ROLLBACK callbacks and commit dangling transactions
 433          *
 434          * @return Exception|null The first exception or null if there were none
 435          */
 436         public function runMasterTransactionIdleCallbacks();
 437
 438         /**
 439          * Run all recurring post-COMMIT/ROLLBACK listener callbacks
 440          *
 441          * @return Exception|null The first exception or null if there were none
 442          */
 443         public function runMasterTransactionListenerCallbacks();
 444
 445         /**
 446          * Issue ROLLBACK only on master, only if queries were done on connection
 447          * @param string $fname Caller name
 448          * @throws DBExpectedError
 449          */
 450         public function rollbackMasterChanges( $fname = __METHOD__ );
 451
 452         /**
 453          * Commit all replica DB transactions so as to flush any REPEATABLE-READ or SSI snapshots
 454          *
 455          * @param string $fname Caller name
 456          */
 457         public function flushReplicaSnapshots( $fname = __METHOD__ );
 458
 459         /**
 460          * Commit all master DB transactions so as to flush any REPEATABLE-READ or SSI snapshots
 461          *
 462          * An error will be thrown if a connection has pending writes or callbacks
 463          *
 464          * @param string $fname Caller name
 465          */
 466         public function flushMasterSnapshots( $fname = __METHOD__ );
 467
 468         /**
 469          * @return bool Whether a master connection is already open
 470          */
 471         public function hasMasterConnection();
 472
 473         /**
 474          * Whether there are pending changes or callbacks in a transaction by this thread
 475          * @return bool
 476          */
 477         public function hasMasterChanges();
 478
 479         /**
 480          * Get the timestamp of the latest write query done by this thread
 481          * @return float|bool UNIX timestamp or false
 482          */
 483         public function lastMasterChangeTimestamp();
 484
 485         /**
 486          * Check if this load balancer object had any recent or still
 487          * pending writes issued against it by this PHP thread
 488          *
 489          * @param float $age How many seconds ago is "recent" [defaults to mWaitTimeout]
 490          * @return bool
 491          */
 492         public function hasOrMadeRecentMasterChanges( $age = null );
 493
 494         /**
 495          * Get the list of callers that have pending master changes
 496          *
 497          * @return string[] List of method names
 498          */
 499         public function pendingMasterChangeCallers();
 500
 501         /**
 502          * @note This method will trigger a DB connection if not yet done
 503          * @param string|bool $domain Domain ID, or false for the current domain
 504          * @return bool Whether the database for generic connections this request is highly "lagged"
 505          */
 506         public function getLaggedReplicaMode( $domain = false );
 507
 508         /**
 509          * Checks whether the database for generic connections this request was both:
 510          *   - a) Already choosen due to a prior connection attempt
 511          *   - b) Considered highly "lagged"
 512          *
 513          * @note This method will never cause a new DB connection
 514          * @return bool
 515          */
 516         public function laggedReplicaUsed();
 517
 518         /**
 519          * @note This method may trigger a DB connection if not yet done
 520          * @param string|bool $domain Domain ID, or false for the current domain
 521          * @param IDatabase|null $conn DB master connection; used to avoid loops [optional]
 522          * @return string|bool Reason the master is read-only or false if it is not
 523          */
 524         public function getReadOnlyReason( $domain = false, IDatabase $conn = null );
 525
 526         /**
 527          * Disables/enables lag checks
 528          * @param null|bool $mode
 529          * @return bool
 530          */
 531         public function allowLagged( $mode = null );
 532
 533         /**
 534          * @return bool
 535          */
 536         public function pingAll();
 537
 538         /**
 539          * Call a function with each open connection object
 540          * @param callable $callback
 541          * @param array $params
 542          */
 543         public function forEachOpenConnection( $callback, array $params = [] );
 544
 545         /**
 546          * Call a function with each open connection object to a master
 547          * @param callable $callback
 548          * @param array $params
 549          */
 550         public function forEachOpenMasterConnection( $callback, array $params = [] );
 551
 552         /**
 553          * Call a function with each open replica DB connection object
 554          * @param callable $callback
 555          * @param array $params
 556          */
 557         public function forEachOpenReplicaConnection( $callback, array $params = [] );
 558
 559         /**
 560          * Get the hostname and lag time of the most-lagged replica DB
 561          *
 562          * This is useful for maintenance scripts that need to throttle their updates.
 563          * May attempt to open connections to replica DBs on the default DB. If there is
 564          * no lag, the maximum lag will be reported as -1.
 565          *
 566          * @param bool|string $domain Domain ID, or false for the default database
 567          * @return array ( host, max lag, index of max lagged host )
 568          */
 569         public function getMaxLag( $domain = false );
 570
 571         /**
 572          * Get an estimate of replication lag (in seconds) for each server
 573          *
 574          * Results are cached for a short time in memcached/process cache
 575          *
 576          * Values may be "false" if replication is too broken to estimate
 577          *
 578          * @param string|bool $domain
 579          * @return int[] Map of (server index => float|int|bool)
 580          */
 581         public function getLagTimes( $domain = false );
 582
 583         /**
 584          * Get the lag in seconds for a given connection, or zero if this load
 585          * balancer does not have replication enabled.
 586          *
 587          * This should be used in preference to Database::getLag() in cases where
 588          * replication may not be in use, since there is no way to determine if
 589          * replication is in use at the connection level without running
 590          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
 591          * function instead of Database::getLag() avoids a fatal error in this
 592          * case on many installations.
 593          *
 594          * @param IDatabase $conn
 595          * @return int|bool Returns false on error
 596          */
 597         public function safeGetLag( IDatabase $conn );
 598
 599         /**
 600          * Wait for a replica DB to reach a specified master position
 601          *
 602          * This will connect to the master to get an accurate position if $pos is not given
 603          *
 604          * @param IDatabase $conn Replica DB
 605          * @param DBMasterPos|bool $pos Master position; default: current position
 606          * @param int $timeout Timeout in seconds [optional]
 607          * @return bool Success
 608          */
 609         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = 10 );
 610
 611         /**
 612          * Set a callback via IDatabase::setTransactionListener() on
 613          * all current and future master connections of this load balancer
 614          *
 615          * @param string $name Callback name
 616          * @param callable|null $callback
 617          */
 618         public function setTransactionListener( $name, callable $callback = null );
 619
 620         /**
 621          * Set a new table prefix for the existing local domain ID for testing
 622          *
 623          * @param string $prefix
 624          */
 625         public function setDomainPrefix( $prefix );
 626
 627         /**
 628          * Make certain table names use their own database, schema, and table prefix
 629          * when passed into SQL queries pre-escaped and without a qualified database name
 630          *
 631          * For example, "user" can be converted to "myschema.mydbname.user" for convenience.
 632          * Appearances like `user`, somedb.user, somedb.someschema.user will used literally.
 633          *
 634          * Calling this twice will completely clear any old table aliases. Also, note that
 635          * callers are responsible for making sure the schemas and databases actually exist.
 636          *
 637          * @param array[] $aliases Map of (table => (dbname, schema, prefix) map)
 638          */
 639         public function setTableAliases( array $aliases );
 640
 641         /**
 642          * Convert certain index names to alternative names before querying the DB
 643          *
 644          * Note that this applies to indexes regardless of the table they belong to.
 645          *
 646          * This can be employed when an index was renamed X => Y in code, but the new Y-named
 647          * indexes were not yet built on all DBs. After all the Y-named ones are added by the DBA,
 648          * the aliases can be removed, and then the old X-named indexes dropped.
 649          *
 650          * @param string[] $aliases
 651          * @return mixed
 652          * @since 1.31
 653          */
 654         public function setIndexAliases( array $aliases );
 655 }