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_AUTO = 1;
  89
  90         /**
  91          * Construct a manager of IDatabase connection objects
  92          *
  93          * @param array $params Parameter map with keys:
  94          *  - servers : Required. Array of server info structures.
  95          *  - localDomain: A DatabaseDomain or domain ID string.
  96          *  - loadMonitor : Name of a class used to fetch server lag and load.
  97          *  - readOnlyReason : Reason the master DB is read-only if so [optional]
  98          *  - waitTimeout : Maximum time to wait for replicas for consistency [optional]
  99          *  - maxLag: Avoid replica DB servers with more lag than this [optional]
 100          *  - srvCache : BagOStuff object for server cache [optional]
 101          *  - wanCache : WANObjectCache object [optional]
 102          *  - chronologyProtector: ChronologyProtector object [optional]
 103          *  - hostname : The name of the current server [optional]
 104          *  - cliMode: Whether the execution context is a CLI script. [optional]
 105          *  - profiler : Class name or instance with profileIn()/profileOut() methods. [optional]
 106          *  - trxProfiler: TransactionProfiler instance. [optional]
 107          *  - replLogger: PSR-3 logger instance. [optional]
 108          *  - connLogger: PSR-3 logger instance. [optional]
 109          *  - queryLogger: PSR-3 logger instance. [optional]
 110          *  - perfLogger: PSR-3 logger instance. [optional]
 111          *  - errorLogger : Callback that takes an Exception and logs it. [optional]
 112          * @throws InvalidArgumentException
 113          */
 114         public function __construct( array $params );
 115
 116         /**
 117          * Get the index of the reader connection, which may be a replica DB
 118          *
 119          * This takes into account load ratios and lag times. It should
 120          * always return a consistent index during a given invocation.
 121          *
 122          * Side effect: opens connections to databases
 123          * @param string|bool $group Query group, or false for the generic reader
 124          * @param string|bool $domain Domain ID, or false for the current domain
 125          * @throws DBError
 126          * @return bool|int|string
 127          */
 128         public function getReaderIndex( $group = false, $domain = false );
 129
 130         /**
 131          * Set the master wait position
 132          *
 133          * If a DB_REPLICA connection has been opened already, then wait immediately.
 134          * Otherwise sets a variable telling it to wait if such a connection is opened.
 135          *
 136          * This only applies to connections to the generic replica DB for this request.
 137          * If a timeout happens when waiting, then getLaggedReplicaMode()/laggedReplicaUsed()
 138          * will return true.
 139          *
 140          * @param DBMasterPos|bool $pos Master position or false
 141          */
 142         public function waitFor( $pos );
 143
 144         /**
 145          * Set the master wait position and wait for a "generic" replica DB to catch up to it
 146          *
 147          * This can be used a faster proxy for waitForAll()
 148          *
 149          * @param DBMasterPos|bool $pos Master position or false
 150          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 151          * @return bool Success (able to connect and no timeouts reached)
 152          */
 153         public function waitForOne( $pos, $timeout = null );
 154
 155         /**
 156          * Set the master wait position and wait for ALL replica DBs to catch up to it
 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 waitForAll( $pos, $timeout = null );
 163
 164         /**
 165          * Get any open connection to a given server index, local or foreign
 166          *
 167          * @param int $i Server index or DB_MASTER/DB_REPLICA
 168          * @return Database|bool False if no such connection is open
 169          */
 170         public function getAnyOpenConnection( $i );
 171
 172         /**
 173          * Get a connection by index
 174          *
 175          * Avoid using CONN_TRX_AUTO with sqlite (e.g. check getServerType() first)
 176          *
 177          * @param int $i Server index or DB_MASTER/DB_REPLICA
 178          * @param array|string|bool $groups Query group(s), or false for the generic reader
 179          * @param string|bool $domain Domain ID, or false for the current domain
 180          * @param int $flags Bitfield of CONN_* class constants
 181          *
 182          * @throws DBError
 183          * @return Database
 184          */
 185         public function getConnection( $i, $groups = [], $domain = false, $flags = 0 );
 186
 187         /**
 188          * Mark a foreign connection as being available for reuse under a different DB domain
 189          *
 190          * This mechanism is reference-counted, and must be called the same number of times
 191          * as getConnection() to work.
 192          *
 193          * @param IDatabase $conn
 194          * @throws InvalidArgumentException
 195          */
 196         public function reuseConnection( $conn );
 197
 198         /**
 199          * Get a database connection handle reference
 200          *
 201          * The handle's methods simply wrap those of a Database handle
 202          *
 203          * Avoid using CONN_TRX_AUTO with sqlite (e.g. check getServerType() first)
 204          *
 205          * @see ILoadBalancer::getConnection() for parameter information
 206          *
 207          * @param int $i Server index or DB_MASTER/DB_REPLICA
 208          * @param array|string|bool $groups Query group(s), or false for the generic reader
 209          * @param string|bool $domain Domain ID, or false for the current domain
 210          * @param int $flags Bitfield of CONN_* class constants (e.g. CONN_TRX_AUTO)
 211          * @return DBConnRef
 212          */
 213         public function getConnectionRef( $i, $groups = [], $domain = false, $flags = 0 );
 214
 215         /**
 216          * Get a database connection handle reference without connecting yet
 217          *
 218          * The handle's methods simply wrap those of a Database handle
 219          *
 220          * Avoid using CONN_TRX_AUTO with sqlite (e.g. check getServerType() first)
 221          *
 222          * @see ILoadBalancer::getConnection() for parameter information
 223          *
 224          * @param int $i Server index or DB_MASTER/DB_REPLICA
 225          * @param array|string|bool $groups Query group(s), or false for the generic reader
 226          * @param string|bool $domain Domain ID, or false for the current domain
 227          * @param int $flags Bitfield of CONN_* class constants (e.g. CONN_TRX_AUTO)
 228          * @return DBConnRef
 229          */
 230         public function getLazyConnectionRef( $i, $groups = [], $domain = false, $flags = 0 );
 231
 232         /**
 233          * Get a maintenance database connection handle reference for migrations and schema changes
 234          *
 235          * The handle's methods simply wrap those of a Database handle
 236          *
 237          * Avoid using CONN_TRX_AUTO with sqlite (e.g. check getServerType() first)
 238          *
 239          * @see ILoadBalancer::getConnection() for parameter information
 240          *
 241          * @param int $db Server index or DB_MASTER/DB_REPLICA
 242          * @param array|string|bool $groups Query group(s), or false for the generic reader
 243          * @param string|bool $domain Domain ID, or false for the current domain
 244          * @param int $flags Bitfield of CONN_* class constants (e.g. CONN_TRX_AUTO)
 245          * @return MaintainableDBConnRef
 246          */
 247         public function getMaintenanceConnectionRef( $db, $groups = [], $domain = false, $flags = 0 );
 248
 249         /**
 250          * Open a connection to the server given by the specified index
 251          *
 252          * The index must be an actual index into the array. If a connection to the server is
 253          * already open and not considered an "in use" foreign connection, this simply returns it.
 254          *
 255          * Avoid using CONN_TRX_AUTO with sqlite (e.g. check getServerType() first)
 256          *
 257          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 258          *
 259          * @param int $i Server index (does not support DB_MASTER/DB_REPLICA)
 260          * @param string|bool $domain Domain ID, or false for the current domain
 261          * @param int $flags Bitfield of CONN_* class constants (e.g. CONN_TRX_AUTO)
 262          * @return Database|bool Returns false on errors
 263          * @throws DBAccessError
 264          */
 265         public function openConnection( $i, $domain = false, $flags = 0 );
 266
 267         /**
 268          * @return int
 269          */
 270         public function getWriterIndex();
 271
 272         /**
 273          * Returns true if the specified index is a valid server index
 274          *
 275          * @param int $i
 276          * @return bool
 277          */
 278         public function haveIndex( $i );
 279
 280         /**
 281          * Returns true if the specified index is valid and has non-zero load
 282          *
 283          * @param int $i
 284          * @return bool
 285          */
 286         public function isNonZeroLoad( $i );
 287
 288         /**
 289          * Get the number of defined servers (not the number of open connections)
 290          *
 291          * @return int
 292          */
 293         public function getServerCount();
 294
 295         /**
 296          * Get the host name or IP address of the server with the specified index
 297          *
 298          * @param int $i
 299          * @return string Readable name if available or IP/host otherwise
 300          */
 301         public function getServerName( $i );
 302
 303         /**
 304          * Get DB type of the server with the specified index
 305          *
 306          * @param int $i
 307          * @return string One of (mysql,postgres,sqlite,...) or "unknown" for bad indexes
 308          * @since 1.30
 309          */
 310         public function getServerType( $i );
 311
 312         /**
 313          * Get the current master position for chronology control purposes
 314          * @return DBMasterPos|bool Returns false if not applicable
 315          */
 316         public function getMasterPos();
 317
 318         /**
 319          * Disable this load balancer. All connections are closed, and any attempt to
 320          * open a new connection will result in a DBAccessError.
 321          */
 322         public function disable();
 323
 324         /**
 325          * Close all open connections
 326          */
 327         public function closeAll();
 328
 329         /**
 330          * Close a connection
 331          *
 332          * Using this function makes sure the LoadBalancer knows the connection is closed.
 333          * If you use $conn->close() directly, the load balancer won't update its state.
 334          *
 335          * @param IDatabase $conn
 336          */
 337         public function closeConnection( IDatabase $conn );
 338
 339         /**
 340          * Commit transactions on all open connections
 341          * @param string $fname Caller name
 342          * @throws DBExpectedError
 343          */
 344         public function commitAll( $fname = __METHOD__ );
 345
 346         /**
 347          * Perform all pre-commit callbacks that remain part of the atomic transactions
 348          * and disable any post-commit callbacks until runMasterPostTrxCallbacks()
 349          *
 350          * Use this only for mutli-database commits
 351          */
 352         public function finalizeMasterChanges();
 353
 354         /**
 355          * Perform all pre-commit checks for things like replication safety
 356          *
 357          * Use this only for mutli-database commits
 358          *
 359          * @param array $options Includes:
 360          *   - maxWriteDuration : max write query duration time in seconds
 361          * @throws DBTransactionError
 362          */
 363         public function approveMasterChanges( array $options );
 364
 365         /**
 366          * Flush any master transaction snapshots and set DBO_TRX (if DBO_DEFAULT is set)
 367          *
 368          * The DBO_TRX setting will be reverted to the default in each of these methods:
 369          *   - commitMasterChanges()
 370          *   - rollbackMasterChanges()
 371          *   - commitAll()
 372          * This allows for custom transaction rounds from any outer transaction scope.
 373          *
 374          * @param string $fname
 375          * @throws DBExpectedError
 376          */
 377         public function beginMasterChanges( $fname = __METHOD__ );
 378
 379         /**
 380          * Issue COMMIT on all master connections where writes where done
 381          * @param string $fname Caller name
 382          * @throws DBExpectedError
 383          */
 384         public function commitMasterChanges( $fname = __METHOD__ );
 385
 386         /**
 387          * Issue all pending post-COMMIT/ROLLBACK callbacks
 388          *
 389          * Use this only for mutli-database commits
 390          *
 391          * @param int $type IDatabase::TRIGGER_* constant
 392          * @return Exception|null The first exception or null if there were none
 393          */
 394         public function runMasterPostTrxCallbacks( $type );
 395
 396         /**
 397          * Issue ROLLBACK only on master, only if queries were done on connection
 398          * @param string $fname Caller name
 399          * @throws DBExpectedError
 400          */
 401         public function rollbackMasterChanges( $fname = __METHOD__ );
 402
 403         /**
 404          * Suppress all pending post-COMMIT/ROLLBACK callbacks
 405          *
 406          * Use this only for mutli-database commits
 407          *
 408          * @return Exception|null The first exception or null if there were none
 409          */
 410         public function suppressTransactionEndCallbacks();
 411
 412         /**
 413          * Commit all replica DB transactions so as to flush any REPEATABLE-READ or SSI snapshot
 414          *
 415          * @param string $fname Caller name
 416          */
 417         public function flushReplicaSnapshots( $fname = __METHOD__ );
 418
 419         /**
 420          * @return bool Whether a master connection is already open
 421          */
 422         public function hasMasterConnection();
 423
 424         /**
 425          * Determine if there are pending changes in a transaction by this thread
 426          * @return bool
 427          */
 428         public function hasMasterChanges();
 429
 430         /**
 431          * Get the timestamp of the latest write query done by this thread
 432          * @return float|bool UNIX timestamp or false
 433          */
 434         public function lastMasterChangeTimestamp();
 435
 436         /**
 437          * Check if this load balancer object had any recent or still
 438          * pending writes issued against it by this PHP thread
 439          *
 440          * @param float $age How many seconds ago is "recent" [defaults to mWaitTimeout]
 441          * @return bool
 442          */
 443         public function hasOrMadeRecentMasterChanges( $age = null );
 444
 445         /**
 446          * Get the list of callers that have pending master changes
 447          *
 448          * @return string[] List of method names
 449          */
 450         public function pendingMasterChangeCallers();
 451
 452         /**
 453          * @note This method will trigger a DB connection if not yet done
 454          * @param string|bool $domain Domain ID, or false for the current domain
 455          * @return bool Whether the database for generic connections this request is highly "lagged"
 456          */
 457         public function getLaggedReplicaMode( $domain = false );
 458
 459         /**
 460          * Checks whether the database for generic connections this request was both:
 461          *   - a) Already choosen due to a prior connection attempt
 462          *   - b) Considered highly "lagged"
 463          *
 464          * @note This method will never cause a new DB connection
 465          * @return bool
 466          */
 467         public function laggedReplicaUsed();
 468
 469         /**
 470          * @note This method may trigger a DB connection if not yet done
 471          * @param string|bool $domain Domain ID, or false for the current domain
 472          * @param IDatabase|null $conn DB master connection; used to avoid loops [optional]
 473          * @return string|bool Reason the master is read-only or false if it is not
 474          */
 475         public function getReadOnlyReason( $domain = false, IDatabase $conn = null );
 476
 477         /**
 478          * Disables/enables lag checks
 479          * @param null|bool $mode
 480          * @return bool
 481          */
 482         public function allowLagged( $mode = null );
 483
 484         /**
 485          * @return bool
 486          */
 487         public function pingAll();
 488
 489         /**
 490          * Call a function with each open connection object
 491          * @param callable $callback
 492          * @param array $params
 493          */
 494         public function forEachOpenConnection( $callback, array $params = [] );
 495
 496         /**
 497          * Call a function with each open connection object to a master
 498          * @param callable $callback
 499          * @param array $params
 500          */
 501         public function forEachOpenMasterConnection( $callback, array $params = [] );
 502
 503         /**
 504          * Call a function with each open replica DB connection object
 505          * @param callable $callback
 506          * @param array $params
 507          */
 508         public function forEachOpenReplicaConnection( $callback, array $params = [] );
 509
 510         /**
 511          * Get the hostname and lag time of the most-lagged replica DB
 512          *
 513          * This is useful for maintenance scripts that need to throttle their updates.
 514          * May attempt to open connections to replica DBs on the default DB. If there is
 515          * no lag, the maximum lag will be reported as -1.
 516          *
 517          * @param bool|string $domain Domain ID, or false for the default database
 518          * @return array ( host, max lag, index of max lagged host )
 519          */
 520         public function getMaxLag( $domain = false );
 521
 522         /**
 523          * Get an estimate of replication lag (in seconds) for each server
 524          *
 525          * Results are cached for a short time in memcached/process cache
 526          *
 527          * Values may be "false" if replication is too broken to estimate
 528          *
 529          * @param string|bool $domain
 530          * @return int[] Map of (server index => float|int|bool)
 531          */
 532         public function getLagTimes( $domain = false );
 533
 534         /**
 535          * Get the lag in seconds for a given connection, or zero if this load
 536          * balancer does not have replication enabled.
 537          *
 538          * This should be used in preference to Database::getLag() in cases where
 539          * replication may not be in use, since there is no way to determine if
 540          * replication is in use at the connection level without running
 541          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
 542          * function instead of Database::getLag() avoids a fatal error in this
 543          * case on many installations.
 544          *
 545          * @param IDatabase $conn
 546          * @return int|bool Returns false on error
 547          */
 548         public function safeGetLag( IDatabase $conn );
 549
 550         /**
 551          * Wait for a replica DB to reach a specified master position
 552          *
 553          * This will connect to the master to get an accurate position if $pos is not given
 554          *
 555          * @param IDatabase $conn Replica DB
 556          * @param DBMasterPos|bool $pos Master position; default: current position
 557          * @param int $timeout Timeout in seconds [optional]
 558          * @return bool Success
 559          */
 560         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = 10 );
 561
 562         /**
 563          * Set a callback via IDatabase::setTransactionListener() on
 564          * all current and future master connections of this load balancer
 565          *
 566          * @param string $name Callback name
 567          * @param callable|null $callback
 568          */
 569         public function setTransactionListener( $name, callable $callback = null );
 570
 571         /**
 572          * Set a new table prefix for the existing local domain ID for testing
 573          *
 574          * @param string $prefix
 575          */
 576         public function setDomainPrefix( $prefix );
 577
 578         /**
 579          * Make certain table names use their own database, schema, and table prefix
 580          * when passed into SQL queries pre-escaped and without a qualified database name
 581          *
 582          * For example, "user" can be converted to "myschema.mydbname.user" for convenience.
 583          * Appearances like `user`, somedb.user, somedb.someschema.user will used literally.
 584          *
 585          * Calling this twice will completely clear any old table aliases. Also, note that
 586          * callers are responsible for making sure the schemas and databases actually exist.
 587          *
 588          * @param array[] $aliases Map of (table => (dbname, schema, prefix) map)
 589          */
 590         public function setTableAliases( array $aliases );
 591 }