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