--- /dev/null
+<?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_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]
+ * - srvCache : BagOStuff object for server cache [optional]
+ * - wanCache : WANObjectCache object [optional]
+ * - chronologyProtector: ChronologyProtector object [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]
+ * @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
+ *
+ * @param int $i Server index or DB_MASTER/DB_REPLICA
+ * @return Database|bool False if no such connection is open
+ */
+ public function getAnyOpenConnection( $i );
+
+ /**
+ * Get a connection by index
+ *
+ * Avoid using CONN_TRX_AUTO with sqlite (e.g. check getServerType() first)
+ *
+ * @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
+ *
+ * @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( $conn );
+
+ /**
+ * Get a database connection handle reference
+ *
+ * The handle's methods simply wrap those of a Database handle
+ *
+ * Avoid using CONN_TRX_AUTO with sqlite (e.g. check getServerType() first)
+ *
+ * @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_AUTO)
+ * @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
+ *
+ * Avoid using CONN_TRX_AUTO with sqlite (e.g. check getServerType() first)
+ *
+ * @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_AUTO)
+ * @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
+ *
+ * Avoid using CONN_TRX_AUTO with sqlite (e.g. check getServerType() first)
+ *
+ * @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_AUTO)
+ * @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_AUTO with sqlite (e.g. check getServerType() first)
+ *
+ * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
+ *
+ * @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_AUTO)
+ * @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
+ *
+ * @deprecated Since 1.30, no alternative
+ */
+ public function getServerInfo( $i );
+
+ /**
+ * Sets the server info structure for the given index. Entry at index $i
+ * is created if it doesn't exist
+ * @param int $i
+ * @param array $serverInfo
+ *
+ * @deprecated Since 1.30, construct new object
+ */
+ public function setServerInfo( $i, array $serverInfo );
+
+ /**
+ * 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 );
+}
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