Make DB handles inherit configured read-only mode

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

diff --git a/includes/db/loadbalancer/LoadBalancer.php b/includes/db/loadbalancer/LoadBalancer.php
index fbc8c8c..bc9465b 100644 (file)
--- a/includes/db/loadbalancer/LoadBalancer.php
+++ b/includes/db/loadbalancer/LoadBalancer.php
@@ -55,9 +55,13 @@ class LoadBalancer {
        /** @var bool|DBMasterPos False if not set */
        private $mWaitForPos;
        /** @var bool Whether the generic reader fell back to a lagged slave */
-       private $mLaggedSlaveMode;
+       private $laggedSlaveMode = false;
+       /** @var bool Whether the generic reader fell back to a lagged slave */
+       private $slavesDownMode = false;
        /** @var string The last DB selection or connection error */
        private $mLastError = 'Unknown error';
+       /** @var string|bool Reason the LB is read-only or false if not */
+       private $readOnlyReason = false;
        /** @var integer Total connections opened */
        private $connsOpened = 0;
 
@@ -68,8 +72,9 @@ class LoadBalancer {
 
        /**
         * @param array $params Array with keys:
-        *   servers           Required. Array of server info structures.
-        *   loadMonitor       Name of a class used to fetch server lag and load.
+        *  - servers : Required. Array of server info structures.
+        *  - loadMonitor : Name of a class used to fetch server lag and load.
+        *  - readOnlyReason : Reason the master DB is read-only if so [optional]
         * @throws MWException
         */
        public function __construct( array $params ) {
@@ -87,10 +92,13 @@ class LoadBalancer {
                        'foreignFree' => array() );
                $this->mLoads = array();
                $this->mWaitForPos = false;
-               $this->mLaggedSlaveMode = false;
                $this->mErrorConnection = false;
                $this->mAllowLagged = false;
 
+               if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
+                       $this->readOnlyReason = $params['readOnlyReason'];
+               }
+
                if ( isset( $params['loadMonitor'] ) ) {
                        $this->mLoadMonitorClass = $params['loadMonitor'];
                } else {
@@ -154,7 +162,7 @@ class LoadBalancer {
        /**
         * @param array $loads
         * @param bool|string $wiki Wiki to get non-lagged for
-        * @param float $maxLag Restrict the maximum allowed lag to this many seconds
+        * @param int $maxLag Restrict the maximum allowed lag to this many seconds
         * @return bool|int|string
         */
        private function getRandomNonLagged( array $loads, $wiki = false, $maxLag = self::MAX_LAG ) {
@@ -329,7 +337,7 @@ class LoadBalancer {
                                $this->mReadIndex = $i;
                                # Record if the generic reader index is in "lagged slave" mode
                                if ( $laggedSlaveMode ) {
-                                       $this->mLaggedSlaveMode = true;
+                                       $this->laggedSlaveMode = true;
                                }
                        }
                        $serverName = $this->getServerName( $i );
@@ -352,7 +360,7 @@ class LoadBalancer {
                if ( $i > 0 ) {
                        if ( !$this->doWait( $i ) ) {
                                $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
-                               $this->mLaggedSlaveMode = true;
+                               $this->laggedSlaveMode = true;
                        }
                }
        }
@@ -548,12 +556,9 @@ class LoadBalancer {
                        $trxProf->recordConnection( $host, $dbname, $masterOnly );
                }
 
-               # Make master connections read only if in lagged slave mode
-               if ( $masterOnly && $this->getServerCount() > 1 && $this->getLaggedSlaveMode() ) {
-                       $conn->setLBInfo( 'readOnlyReason',
-                               'The database has been automatically locked ' .
-                               'while the slave database servers catch up to the master'
-                       );
+               if ( $masterOnly ) {
+                       # Make master-requested DB handles inherit any read-only mode setting
+                       $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $wiki ) );
                }
 
                return $conn;
@@ -1142,13 +1147,24 @@ class LoadBalancer {
 
        /**
         * @note This method will trigger a DB connection if not yet done
+        *
+        * @param string|bool $wiki Wiki ID, or false for the current wiki
         * @return bool Whether the generic connection for reads is highly "lagged"
         */
-       public function getLaggedSlaveMode() {
-               # Get a generic reader connection
-               $this->getConnection( DB_SLAVE );
+       public function getLaggedSlaveMode( $wiki = false ) {
+               // No-op if there is only one DB (also avoids recursion)
+               if ( !$this->laggedSlaveMode && $this->getServerCount() > 1 ) {
+                       try {
+                               // See if laggedSlaveMode gets set
+                               $this->getConnection( DB_SLAVE, false, $wiki );
+                       } catch ( DBConnectionError $e ) {
+                               // Avoid expensive re-connect attempts and failures
+                               $this->slavesDownMode = true;
+                               $this->laggedSlaveMode = true;
+                       }
+               }
 
-               return $this->mLaggedSlaveMode;
+               return $this->laggedSlaveMode;
        }
 
        /**
@@ -1157,7 +1173,29 @@ class LoadBalancer {
         * @since 1.27
         */
        public function laggedSlaveUsed() {
-               return $this->mLaggedSlaveMode;
+               return $this->laggedSlaveMode;
+       }
+
+       /**
+        * @note This method may trigger a DB connection if not yet done
+        * @param string|bool $wiki Wiki ID, or false for the current wiki
+        * @return string|bool Reason the master is read-only or false if it is not
+        * @since 1.27
+        */
+       public function getReadOnlyReason( $wiki = false ) {
+               if ( $this->readOnlyReason !== false ) {
+                       return $this->readOnlyReason;
+               } elseif ( $this->getLaggedSlaveMode( $wiki ) ) {
+                       if ( $this->slavesDownMode ) {
+                               return 'The database has been automatically locked ' .
+                                       'until the slave database servers become available';
+                       } else {
+                               return 'The database has been automatically locked ' .
+                                       'while the slave database servers catch up to the master.';
+                       }
+               }
+
+               return false;
        }
 
        /**