diff options
Diffstat (limited to 'www/wiki/includes/libs/rdbms/loadbalancer/ILoadBalancer.php')
| -rw-r--r-- | www/wiki/includes/libs/rdbms/loadbalancer/ILoadBalancer.php | 647 |
1 files changed, 647 insertions, 0 deletions
diff --git a/www/wiki/includes/libs/rdbms/loadbalancer/ILoadBalancer.php b/www/wiki/includes/libs/rdbms/loadbalancer/ILoadBalancer.php new file mode 100644 index 00000000..d6b7e3bd --- /dev/null +++ b/www/wiki/includes/libs/rdbms/loadbalancer/ILoadBalancer.php @@ -0,0 +1,647 @@ +<?php +/** + * Database load balancing interface + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License along + * with this program; if not, write to the Free Software Foundation, Inc., + * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. + * http://www.gnu.org/copyleft/gpl.html + * + * @file + * @ingroup Database + */ +namespace Wikimedia\Rdbms; + +use Exception; +use InvalidArgumentException; + +/** + * Database cluster connection, tracking, load balancing, and transaction manager interface + * + * A "cluster" is considered to be one master database and zero or more replica databases. + * Typically, the replica DBs replicate from the master asynchronously. The first node in the + * "servers" configuration array is always considered the "master". However, this class can still + * be used when all or some of the "replica" DBs are multi-master peers of the master or even + * when all the DBs are non-replicating clones of each other holding read-only data. Thus, the + * role of "master" is in some cases merely nominal. + * + * By default, each DB server uses DBO_DEFAULT for its 'flags' setting, unless explicitly set + * otherwise in configuration. DBO_DEFAULT behavior depends on whether 'cliMode' is set: + * - In CLI mode, the flag has no effect with regards to LoadBalancer. + * - In non-CLI mode, the flag causes implicit transactions to be used; the first query on + * a database starts a transaction on that database. The transactions are meant to remain + * pending until either commitMasterChanges() or rollbackMasterChanges() is called. The + * application must have some point where it calls commitMasterChanges() near the end of + * the PHP request. + * Every iteration of beginMasterChanges()/commitMasterChanges() is called a "transaction round". + * Rounds are useful on the master DB connections because they make single-DB (and by and large + * multi-DB) updates in web requests all-or-nothing. Also, transactions on replica DBs are useful + * when REPEATABLE-READ or SERIALIZABLE isolation is used because all foriegn keys and constraints + * hold across separate queries in the DB transaction since the data appears within a consistent + * point-in-time snapshot. + * + * The typical caller will use LoadBalancer::getConnection( DB_* ) to yield a live database + * connection handle. The choice of which DB server to use is based on pre-defined loads for + * weighted random selection, adjustments thereof by LoadMonitor, and the amount of replication + * lag on each DB server. Lag checks might cause problems in certain setups, so they should be + * tuned in the server configuration maps as follows: + * - Master + N Replica(s): set 'max lag' to an appropriate threshold for avoiding any database + * lagged by this much or more. If all DBs are this lagged, then the load balancer considers + * the cluster to be read-only. + * - Galera Cluster: Seconds_Behind_Master will be 0, so there probably is nothing to tune. + * Note that lag is still possible depending on how wsrep-sync-wait is set server-side. + * - Read-only archive clones: set 'is static' in the server configuration maps. This will + * treat all such DBs as having 0 lag. + * - SQL load balancing proxy: any proxy should handle lag checks on its own, so the 'max lag' + * parameter should probably be set to INF in the server configuration maps. This will make + * the load balancer ignore whatever it detects as the lag of the logical replica is (which + * would probably just randomly bounce around). + * + * If using a SQL proxy service, it would probably be best to have two proxy hosts for the + * load balancer to talk to. One would be the 'host' of the master server entry and another for + * the (logical) replica server entry. The proxy could map the load balancer's "replica" DB to + * any number of physical replica DBs. + * + * @since 1.28 + * @ingroup Database + */ +interface ILoadBalancer { + /** @var int Request a replica DB connection */ + const DB_REPLICA = -1; + /** @var int Request a master DB connection */ + const DB_MASTER = -2; + + /** @var string Domain specifier when no specific database needs to be selected */ + const DOMAIN_ANY = ''; + + /** @var int DB handle should have DBO_TRX disabled and the caller will leave it as such */ + const CONN_TRX_AUTOCOMMIT = 1; + /** @var int Alias for CONN_TRX_AUTOCOMMIT for b/c; deprecated since 1.31 */ + const CONN_TRX_AUTO = 1; + + /** + * Construct a manager of IDatabase connection objects + * + * @param array $params Parameter map with keys: + * - servers : Required. Array of server info structures. + * - localDomain: A DatabaseDomain or domain ID string. + * - loadMonitor : Name of a class used to fetch server lag and load. + * - readOnlyReason : Reason the master DB is read-only if so [optional] + * - waitTimeout : Maximum time to wait for replicas for consistency [optional] + * - maxLag: Avoid replica DB servers with more lag than this [optional] + * - srvCache : BagOStuff object for server cache [optional] + * - wanCache : WANObjectCache object [optional] + * - chronologyCallback: Callback to run before the first connection attempt [optional] + * - hostname : The name of the current server [optional] + * - cliMode: Whether the execution context is a CLI script. [optional] + * - profiler : Class name or instance with profileIn()/profileOut() methods. [optional] + * - trxProfiler: TransactionProfiler instance. [optional] + * - replLogger: PSR-3 logger instance. [optional] + * - connLogger: PSR-3 logger instance. [optional] + * - queryLogger: PSR-3 logger instance. [optional] + * - perfLogger: PSR-3 logger instance. [optional] + * - errorLogger : Callback that takes an Exception and logs it. [optional] + * - deprecationLogger: Callback to log a deprecation warning. [optional] + * @throws InvalidArgumentException + */ + public function __construct( array $params ); + + /** + * Get the index of the reader connection, which may be a replica DB + * + * This takes into account load ratios and lag times. It should + * always return a consistent index during a given invocation. + * + * Side effect: opens connections to databases + * @param string|bool $group Query group, or false for the generic reader + * @param string|bool $domain Domain ID, or false for the current domain + * @throws DBError + * @return bool|int|string + */ + public function getReaderIndex( $group = false, $domain = false ); + + /** + * Set the master wait position + * + * If a DB_REPLICA connection has been opened already, then wait immediately. + * Otherwise sets a variable telling it to wait if such a connection is opened. + * + * This only applies to connections to the generic replica DB for this request. + * If a timeout happens when waiting, then getLaggedReplicaMode()/laggedReplicaUsed() + * will return true. + * + * @param DBMasterPos|bool $pos Master position or false + */ + public function waitFor( $pos ); + + /** + * Set the master wait position and wait for a "generic" replica DB to catch up to it + * + * This can be used a faster proxy for waitForAll() + * + * @param DBMasterPos|bool $pos Master position or false + * @param int $timeout Max seconds to wait; default is mWaitTimeout + * @return bool Success (able to connect and no timeouts reached) + */ + public function waitForOne( $pos, $timeout = null ); + + /** + * Set the master wait position and wait for ALL replica DBs to catch up to it + * + * @param DBMasterPos|bool $pos Master position or false + * @param int $timeout Max seconds to wait; default is mWaitTimeout + * @return bool Success (able to connect and no timeouts reached) + */ + public function waitForAll( $pos, $timeout = null ); + + /** + * Get any open connection to a given server index, local or foreign + * + * Use CONN_TRX_AUTOCOMMIT to only look for connections opened with that flag + * + * @param int $i Server index or DB_MASTER/DB_REPLICA + * @param int $flags Bitfield of CONN_* class constants + * @return Database|bool False if no such connection is open + */ + public function getAnyOpenConnection( $i, $flags = 0 ); + + /** + * Get a connection handle by server index + * + * The CONN_TRX_AUTOCOMMIT flag is ignored for databases with ATTR_DB_LEVEL_LOCKING + * (e.g. sqlite) in order to avoid deadlocks. ILoadBalancer::getServerAttributes() + * can be used to check such flags beforehand. + * + * If the caller uses $domain or sets CONN_TRX_AUTOCOMMIT in $flags, then it must also + * call ILoadBalancer::reuseConnection() on the handle when finished using it. + * In all other cases, this is not necessary, though not harmful either. + * + * @param int $i Server index (overrides $groups) or DB_MASTER/DB_REPLICA + * @param array|string|bool $groups Query group(s), or false for the generic reader + * @param string|bool $domain Domain ID, or false for the current domain + * @param int $flags Bitfield of CONN_* class constants + * + * @note This method throws DBAccessError if ILoadBalancer::disable() was called + * + * @throws DBError + * @return Database + */ + public function getConnection( $i, $groups = [], $domain = false, $flags = 0 ); + + /** + * Mark a foreign connection as being available for reuse under a different DB domain + * + * This mechanism is reference-counted, and must be called the same number of times + * as getConnection() to work. + * + * @param IDatabase $conn + * @throws InvalidArgumentException + */ + public function reuseConnection( IDatabase $conn ); + + /** + * Get a database connection handle reference + * + * The handle's methods simply wrap those of a Database handle + * + * The CONN_TRX_AUTOCOMMIT flag is ignored for databases with ATTR_DB_LEVEL_LOCKING + * (e.g. sqlite) in order to avoid deadlocks. ILoadBalancer::getServerAttributes() + * can be used to check such flags beforehand. + * + * @see ILoadBalancer::getConnection() for parameter information + * + * @param int $i Server index or DB_MASTER/DB_REPLICA + * @param array|string|bool $groups Query group(s), or false for the generic reader + * @param string|bool $domain Domain ID, or false for the current domain + * @param int $flags Bitfield of CONN_* class constants (e.g. CONN_TRX_AUTOCOMMIT) + * @return DBConnRef + */ + public function getConnectionRef( $i, $groups = [], $domain = false, $flags = 0 ); + + /** + * Get a database connection handle reference without connecting yet + * + * The handle's methods simply wrap those of a Database handle + * + * The CONN_TRX_AUTOCOMMIT flag is ignored for databases with ATTR_DB_LEVEL_LOCKING + * (e.g. sqlite) in order to avoid deadlocks. ILoadBalancer::getServerAttributes() + * can be used to check such flags beforehand. + * + * @see ILoadBalancer::getConnection() for parameter information + * + * @param int $i Server index or DB_MASTER/DB_REPLICA + * @param array|string|bool $groups Query group(s), or false for the generic reader + * @param string|bool $domain Domain ID, or false for the current domain + * @param int $flags Bitfield of CONN_* class constants (e.g. CONN_TRX_AUTOCOMMIT) + * @return DBConnRef + */ + public function getLazyConnectionRef( $i, $groups = [], $domain = false, $flags = 0 ); + + /** + * Get a maintenance database connection handle reference for migrations and schema changes + * + * The handle's methods simply wrap those of a Database handle + * + * The CONN_TRX_AUTOCOMMIT flag is ignored for databases with ATTR_DB_LEVEL_LOCKING + * (e.g. sqlite) in order to avoid deadlocks. ILoadBalancer::getServerAttributes() + * can be used to check such flags beforehand. + * + * @see ILoadBalancer::getConnection() for parameter information + * + * @param int $db Server index or DB_MASTER/DB_REPLICA + * @param array|string|bool $groups Query group(s), or false for the generic reader + * @param string|bool $domain Domain ID, or false for the current domain + * @param int $flags Bitfield of CONN_* class constants (e.g. CONN_TRX_AUTOCOMMIT) + * @return MaintainableDBConnRef + */ + public function getMaintenanceConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ); + + /** + * Open a connection to the server given by the specified index + * + * The index must be an actual index into the array. If a connection to the server is + * already open and not considered an "in use" foreign connection, this simply returns it. + * + * Avoid using CONN_TRX_AUTOCOMMIT for databases with ATTR_DB_LEVEL_LOCKING (e.g. sqlite) in + * order to avoid deadlocks. ILoadBalancer::getServerAttributes() can be used to check + * such flags beforehand. + * + * If the caller uses $domain or sets CONN_TRX_AUTOCOMMIT in $flags, then it must also + * call ILoadBalancer::reuseConnection() on the handle when finished using it. + * In all other cases, this is not necessary, though not harmful either. + * + * @note This method throws DBAccessError if ILoadBalancer::disable() was called + * + * @param int $i Server index (does not support DB_MASTER/DB_REPLICA) + * @param string|bool $domain Domain ID, or false for the current domain + * @param int $flags Bitfield of CONN_* class constants (e.g. CONN_TRX_AUTOCOMMIT) + * @return Database|bool Returns false on errors + * @throws DBAccessError + */ + public function openConnection( $i, $domain = false, $flags = 0 ); + + /** + * @return int + */ + public function getWriterIndex(); + + /** + * Returns true if the specified index is a valid server index + * + * @param int $i + * @return bool + */ + public function haveIndex( $i ); + + /** + * Returns true if the specified index is valid and has non-zero load + * + * @param int $i + * @return bool + */ + public function isNonZeroLoad( $i ); + + /** + * Get the number of defined servers (not the number of open connections) + * + * @return int + */ + public function getServerCount(); + + /** + * Get the host name or IP address of the server with the specified index + * + * @param int $i + * @return string Readable name if available or IP/host otherwise + */ + public function getServerName( $i ); + + /** + * Get DB type of the server with the specified index + * + * @param int $i + * @return string One of (mysql,postgres,sqlite,...) or "unknown" for bad indexes + * @since 1.30 + */ + public function getServerType( $i ); + + /** + * Return the server info structure for a given index, or false if the index is invalid. + * @param int $i + * @return array|bool + * @since 1.31 + */ + public function getServerInfo( $i ); + + /** + * @param int $i Server index + * @return array (Database::ATTRIBUTE_* constant => value) for all such constants + * @since 1.31 + */ + public function getServerAttributes( $i ); + + /** + * Get the current master position for chronology control purposes + * @return DBMasterPos|bool Returns false if not applicable + */ + public function getMasterPos(); + + /** + * Disable this load balancer. All connections are closed, and any attempt to + * open a new connection will result in a DBAccessError. + */ + public function disable(); + + /** + * Close all open connections + */ + public function closeAll(); + + /** + * Close a connection + * + * Using this function makes sure the LoadBalancer knows the connection is closed. + * If you use $conn->close() directly, the load balancer won't update its state. + * + * @param IDatabase $conn + */ + public function closeConnection( IDatabase $conn ); + + /** + * Commit transactions on all open connections + * @param string $fname Caller name + * @throws DBExpectedError + */ + public function commitAll( $fname = __METHOD__ ); + + /** + * Perform all pre-commit callbacks that remain part of the atomic transactions + * and disable any post-commit callbacks until runMasterPostTrxCallbacks() + * + * Use this only for mutli-database commits + */ + public function finalizeMasterChanges(); + + /** + * Perform all pre-commit checks for things like replication safety + * + * Use this only for mutli-database commits + * + * @param array $options Includes: + * - maxWriteDuration : max write query duration time in seconds + * @throws DBTransactionError + */ + public function approveMasterChanges( array $options ); + + /** + * Flush any master transaction snapshots and set DBO_TRX (if DBO_DEFAULT is set) + * + * The DBO_TRX setting will be reverted to the default in each of these methods: + * - commitMasterChanges() + * - rollbackMasterChanges() + * - commitAll() + * This allows for custom transaction rounds from any outer transaction scope. + * + * @param string $fname + * @throws DBExpectedError + */ + public function beginMasterChanges( $fname = __METHOD__ ); + + /** + * Issue COMMIT on all master connections where writes where done + * @param string $fname Caller name + * @throws DBExpectedError + */ + public function commitMasterChanges( $fname = __METHOD__ ); + + /** + * Issue all pending post-COMMIT/ROLLBACK callbacks + * + * Use this only for mutli-database commits + * + * @param int $type IDatabase::TRIGGER_* constant + * @return Exception|null The first exception or null if there were none + */ + public function runMasterPostTrxCallbacks( $type ); + + /** + * Issue ROLLBACK only on master, only if queries were done on connection + * @param string $fname Caller name + * @throws DBExpectedError + */ + public function rollbackMasterChanges( $fname = __METHOD__ ); + + /** + * Suppress all pending post-COMMIT/ROLLBACK callbacks + * + * Use this only for mutli-database commits + * + * @return Exception|null The first exception or null if there were none + */ + public function suppressTransactionEndCallbacks(); + + /** + * Commit all replica DB transactions so as to flush any REPEATABLE-READ or SSI snapshot + * + * @param string $fname Caller name + */ + public function flushReplicaSnapshots( $fname = __METHOD__ ); + + /** + * @return bool Whether a master connection is already open + */ + public function hasMasterConnection(); + + /** + * Determine if there are pending changes in a transaction by this thread + * @return bool + */ + public function hasMasterChanges(); + + /** + * Get the timestamp of the latest write query done by this thread + * @return float|bool UNIX timestamp or false + */ + public function lastMasterChangeTimestamp(); + + /** + * Check if this load balancer object had any recent or still + * pending writes issued against it by this PHP thread + * + * @param float $age How many seconds ago is "recent" [defaults to mWaitTimeout] + * @return bool + */ + public function hasOrMadeRecentMasterChanges( $age = null ); + + /** + * Get the list of callers that have pending master changes + * + * @return string[] List of method names + */ + public function pendingMasterChangeCallers(); + + /** + * @note This method will trigger a DB connection if not yet done + * @param string|bool $domain Domain ID, or false for the current domain + * @return bool Whether the database for generic connections this request is highly "lagged" + */ + public function getLaggedReplicaMode( $domain = false ); + + /** + * Checks whether the database for generic connections this request was both: + * - a) Already choosen due to a prior connection attempt + * - b) Considered highly "lagged" + * + * @note This method will never cause a new DB connection + * @return bool + */ + public function laggedReplicaUsed(); + + /** + * @note This method may trigger a DB connection if not yet done + * @param string|bool $domain Domain ID, or false for the current domain + * @param IDatabase|null $conn DB master connection; used to avoid loops [optional] + * @return string|bool Reason the master is read-only or false if it is not + */ + public function getReadOnlyReason( $domain = false, IDatabase $conn = null ); + + /** + * Disables/enables lag checks + * @param null|bool $mode + * @return bool + */ + public function allowLagged( $mode = null ); + + /** + * @return bool + */ + public function pingAll(); + + /** + * Call a function with each open connection object + * @param callable $callback + * @param array $params + */ + public function forEachOpenConnection( $callback, array $params = [] ); + + /** + * Call a function with each open connection object to a master + * @param callable $callback + * @param array $params + */ + public function forEachOpenMasterConnection( $callback, array $params = [] ); + + /** + * Call a function with each open replica DB connection object + * @param callable $callback + * @param array $params + */ + public function forEachOpenReplicaConnection( $callback, array $params = [] ); + + /** + * Get the hostname and lag time of the most-lagged replica DB + * + * This is useful for maintenance scripts that need to throttle their updates. + * May attempt to open connections to replica DBs on the default DB. If there is + * no lag, the maximum lag will be reported as -1. + * + * @param bool|string $domain Domain ID, or false for the default database + * @return array ( host, max lag, index of max lagged host ) + */ + public function getMaxLag( $domain = false ); + + /** + * Get an estimate of replication lag (in seconds) for each server + * + * Results are cached for a short time in memcached/process cache + * + * Values may be "false" if replication is too broken to estimate + * + * @param string|bool $domain + * @return int[] Map of (server index => float|int|bool) + */ + public function getLagTimes( $domain = false ); + + /** + * Get the lag in seconds for a given connection, or zero if this load + * balancer does not have replication enabled. + * + * This should be used in preference to Database::getLag() in cases where + * replication may not be in use, since there is no way to determine if + * replication is in use at the connection level without running + * potentially restricted queries such as SHOW SLAVE STATUS. Using this + * function instead of Database::getLag() avoids a fatal error in this + * case on many installations. + * + * @param IDatabase $conn + * @return int|bool Returns false on error + */ + public function safeGetLag( IDatabase $conn ); + + /** + * Wait for a replica DB to reach a specified master position + * + * This will connect to the master to get an accurate position if $pos is not given + * + * @param IDatabase $conn Replica DB + * @param DBMasterPos|bool $pos Master position; default: current position + * @param int $timeout Timeout in seconds [optional] + * @return bool Success + */ + public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = 10 ); + + /** + * Set a callback via IDatabase::setTransactionListener() on + * all current and future master connections of this load balancer + * + * @param string $name Callback name + * @param callable|null $callback + */ + public function setTransactionListener( $name, callable $callback = null ); + + /** + * Set a new table prefix for the existing local domain ID for testing + * + * @param string $prefix + */ + public function setDomainPrefix( $prefix ); + + /** + * Make certain table names use their own database, schema, and table prefix + * when passed into SQL queries pre-escaped and without a qualified database name + * + * For example, "user" can be converted to "myschema.mydbname.user" for convenience. + * Appearances like `user`, somedb.user, somedb.someschema.user will used literally. + * + * Calling this twice will completely clear any old table aliases. Also, note that + * callers are responsible for making sure the schemas and databases actually exist. + * + * @param array[] $aliases Map of (table => (dbname, schema, prefix) map) + */ + public function setTableAliases( array $aliases ); + + /** + * Convert certain index names to alternative names before querying the DB + * + * Note that this applies to indexes regardless of the table they belong to. + * + * This can be employed when an index was renamed X => Y in code, but the new Y-named + * indexes were not yet built on all DBs. After all the Y-named ones are added by the DBA, + * the aliases can be removed, and then the old X-named indexes dropped. + * + * @param string[] $aliases + * @return mixed + * @since 1.31 + */ + public function setIndexAliases( array $aliases ); +} |