* 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.
+ * - Externally updated dataset 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
/** @var int DB handle should have DBO_TRX disabled and the caller will leave it as such */
const CONN_TRX_AUTOCOMMIT = 1;
+ /** @var int Return null on connection failure instead of throwing an exception */
+ const CONN_SILENCE_ERRORS = 2;
/** @var string Manager of ILoadBalancer instances is running post-commit callbacks */
const STAGE_POSTCOMMIT_CALLBACKS = 'stage-postcommit-callbacks';
public function redefineLocalDomain( $domain );
/**
- * Get the index of the reader connection, which may be a replica DB
+ * Get the server index of the reader connection for a given group
*
- * This takes into account load ratios and lag times. It should
- * always return a consistent index during a given invocation.
+ * This takes into account load ratios and lag times. It should return a consistent
+ * index during the life time of the load balancer. This initially checks replica DBs
+ * for connectivity to avoid returning an unusable server. This means that connections
+ * might be attempted by calling this method (usally one at the most but possibly more).
+ * Subsequent calls with the same $group will not need to make new connection attempts
+ * since the acquired connection for each group is preserved.
*
- * Side effect: opens connections to databases
* @param string|bool $group Query group, or false for the generic group
* @param string|bool $domain Domain ID, or false for the current domain
* @throws DBError
*
* @note This method throws DBAccessError if ILoadBalancer::disable() was called
*
- * @throws DBError
- * @return Database
+ * @throws DBError If any error occurs that prevents the yielding of a (live) IDatabase
+ * @return IDatabase|bool This returns false on failure if CONN_SILENCE_ERRORS is set
*/
public function getConnection( $i, $groups = [], $domain = false, $flags = 0 );
public function getMaintenanceConnectionRef( $i, $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.
- * Avoid the use of begin() or startAtomic() on any such connections.
+ * Get the server index of the master server
*
- * @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();
public function isNonZeroLoad( $i );
/**
- * Get the number of defined servers (not the number of open connections)
+ * Get the number of servers defined in configuration
*
* @return int
*/
public function getServerCount();
+ /**
+ * Whether there are any replica servers configured
+ *
+ * This counts both servers using streaming replication from the master server and
+ * servers that just have a clone of the static dataset found on the master server
+ *
+ * @return int
+ * @since 1.34
+ */
+ public function hasReplicaServers();
+
+ /**
+ * Whether any replica servers use streaming replication from the master server
+ *
+ * Generally this is one less than getServerCount(), though it might otherwise
+ * return a lower number if some of the servers are configured with "is static".
+ * That flag is used when both the server has no active replication setup and the
+ * dataset is either read-only or occasionally updated out-of-band. For example,
+ * a script might import a new geographic information dataset each week by writing
+ * it to each server and later directing the application to use the new version.
+ *
+ * It is possible for some replicas to be configured with "is static" but not
+ * others, though it generally should either be set for all or none of the replicas.
+ *
+ * If this returns zero, this means that there is generally no reason to execute
+ * replication wait logic for session consistency and lag reduction.
+ *
+ * @return int
+ * @since 1.34
+ */
+ public function hasStreamingReplicaServers();
+
/**
* Get the host name or IP address of the server with the specified index
*
public function forEachOpenReplicaConnection( $callback, array $params = [] );
/**
- * Get the hostname and lag time of the most-lagged replica DB
+ * Get the hostname and lag time of the most-lagged replica server
*
* 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
dépôts / lhc / web / wiklou.git / blobdiff