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<?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
* @author Aaron Schulz
*/
/**
* 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 integer Request a replica DB connection */
const DB_REPLICA = -1;
/** @var integer Request a master DB connection */
const DB_MASTER = -2;
/** @var string Domain specifier when no specific database needs to be selected */
const DOMAIN_ANY = '';
/**
* 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]
* - memCache : BagOStuff object for cluster memory cache [optional]
* - wanCache : WANObjectCache 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, waits
* Otherwise sets a variable telling it to wait if such a connection is opened
* @param DBMasterPos $pos
*/
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 $pos
* @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 $pos
* @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
* Returns false if there is no connection open
*
* @param int $i Server index
* @return IDatabase|bool False on failure
*/
public function getAnyOpenConnection( $i );
/**
* Get a connection by index
* This is the main entry point for this class.
*
* @param int $i Server index
* @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
*
* @throws DBError
* @return IDatabase
*/
public function getConnection( $i, $groups = [], $domain = false );
/**
* Mark a foreign connection as being available for reuse under a different
* DB name or prefix. 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 wrap simply wrap those of a IDatabase handle
*
* @see LoadBalancer::getConnection() for parameter information
*
* @param int $db
* @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
* @return DBConnRef
*/
public function getConnectionRef( $db, $groups = [], $domain = false );
/**
* Get a database connection handle reference without connecting yet
*
* The handle's methods wrap simply wrap those of a IDatabase handle
*
* @see LoadBalancer::getConnection() for parameter information
*
* @param int $db
* @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
* @return DBConnRef
*/
public function getLazyConnectionRef( $db, $groups = [], $domain = false );
/**
* Open a connection to the server given by the specified index
* Index must be an actual index into the array.
* If the server is already open, returns it.
*
* On error, returns false, and the connection which caused the
* error will be available via $this->mErrorConnection.
*
* @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
*
* @param int $i Server index
* @param string|bool $domain Domain ID, or false for the current domain
* @return IDatabase|bool Returns false on errors
* @throws DBAccessError
*/
public function openConnection( $i, $domain = false );
/**
* @return int
*/
public function getWriterIndex();
/**
* Returns true if the specified index is a valid server index
*
* @param string $i
* @return bool
*/
public function haveIndex( $i );
/**
* Returns true if the specified index is valid and has non-zero load
*
* @param string $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
* Prefer a readable name if available.
* @param string $i
* @return string
*/
public function getServerName( $i );
/**
* Return the server info structure for a given index, or false if the index is invalid.
* @param int $i
* @return array|bool
*/
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
*/
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 integer $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 generic connection for reads is highly "lagged"
*/
public function getLaggedReplicaMode( $domain = false );
/**
* @note This method will never cause a new DB connection
* @return bool Whether any generic connection used for reads was highly "lagged"
*/
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 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 integer|null $timeout Timeout in seconds [optional]
* @return bool Success
*/
public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = null );
/**
* 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 );
}