Merge "Deprecate wfWaitForSlaves() with LBFactory::waitForReplication()"

[lhc/web/wiklou.git] / includes / db / loadbalancer / LBFactory.php

diff --git a/includes/db/loadbalancer/LBFactory.php b/includes/db/loadbalancer/LBFactory.php
index 37ab9ca..25fdea9 100644 (file)
--- a/includes/db/loadbalancer/LBFactory.php
+++ b/includes/db/loadbalancer/LBFactory.php
@@ -312,6 +312,90 @@ abstract class LBFactory {
                return $ret;
        }
 
+       /**
+        * Waits for the slave DBs to catch up to the current master position
+        *
+        * Use this when updating very large numbers of rows, as in maintenance scripts,
+        * to avoid causing too much lag. Of course, this is a no-op if there are no slaves.
+        *
+        * By default this waits on all DB clusters actually used in this request.
+        * This makes sense when lag being waiting on is caused by the code that does this check.
+        * In that case, setting "ifWritesSince" can avoid the overhead of waiting for clusters
+        * that were not changed since the last wait check. To forcefully wait on a specific cluster
+        * for a given wiki, use the 'wiki' parameter. To forcefully wait on an "external" cluster,
+        * use the "cluster" parameter.
+        *
+        * Never call this function after a large DB write that is *still* in a transaction.
+        * It only makes sense to call this after the possible lag inducing changes were committed.
+        *
+        * @param array $opts Optional fields that include:
+        *   - wiki : wait on the load balancer DBs that handles the given wiki
+        *   - cluster : wait on the given external load balancer DBs
+        *   - timeout : Max wait time. Default: ~60 seconds
+        *   - ifWritesSince: Only wait if writes were done since this UNIX timestamp
+        * @throws DBReplicationWaitError If a timeout or error occured waiting on a DB cluster
+        * @since 1.27
+        */
+       public function waitForReplication( array $opts = array() ) {
+               $opts += array(
+                       'wiki' => false,
+                       'cluster' => false,
+                       'timeout' => 60,
+                       'ifWritesSince' => null
+               );
+
+               // Figure out which clusters need to be checked
+               /** @var LoadBalancer[] $lbs */
+               $lbs = array();
+               if ( $opts['cluster'] !== false ) {
+                       $lbs[] = $this->getExternalLB( $opts['cluster'] );
+               } elseif ( $opts['wiki'] !== false ) {
+                       $lbs[] = $this->getMainLB( $opts['wiki'] );
+               } else {
+                       $this->forEachLB( function ( LoadBalancer $lb ) use ( &$lbs ) {
+                               $lbs[] = $lb;
+                       } );
+                       if ( !$lbs ) {
+                               return; // nothing actually used
+                       }
+               }
+
+               // Get all the master positions of applicable DBs right now.
+               // This can be faster since waiting on one cluster reduces the
+               // time needed to wait on the next clusters.
+               $masterPositions = array_fill( 0, count( $lbs ), false );
+               foreach ( $lbs as $i => $lb ) {
+                       if ( $lb->getServerCount() <= 1 ) {
+                               // Bug 27975 - Don't try to wait for slaves if there are none
+                               // Prevents permission error when getting master position
+                               continue;
+                       } elseif ( $opts['ifWritesSince']
+                               && $lb->lastMasterChangeTimestamp() < $opts['ifWritesSince']
+                       ) {
+                               continue; // no writes since the last wait
+                       }
+                       $masterPositions[$i] = $lb->getMasterPos();
+               }
+
+               $failed = array();
+               foreach ( $lbs as $i => $lb ) {
+                       if ( $masterPositions[$i] ) {
+                               // The DBMS may not support getMasterPos() or the whole
+                               // load balancer might be fake (e.g. $wgAllDBsAreLocalhost).
+                               if ( !$lb->waitForAll( $masterPositions[$i], $opts['timeout'] ) ) {
+                                       $failed[] = $lb->getServerName( $lb->getWriterIndex() );
+                               }
+                       }
+               }
+
+               if ( $failed ) {
+                       throw new DBReplicationWaitError(
+                               "Could not wait for slaves to catch up to " .
+                               implode( ', ', $failed )
+                       );
+               }
+       }
+
        /**
         * Disable the ChronologyProtector for all load balancers
         *
@@ -378,3 +462,9 @@ class DBAccessError extends MWException {
                        "This is not allowed." );
        }
 }
+
+/**
+ * Exception class for replica DB wait timeouts
+ */
+class DBReplicationWaitError extends Exception {
+}