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