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