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[mediawiki.git] / includes / objectcache / RedisBagOStuff.php

<?php
/**
 * Object caching using Redis (http://redis.io/).
 *
 * 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
 */

class RedisBagOStuff extends BagOStuff {
        /** @var RedisConnectionPool */
        protected $redisPool;
        /** @var Array List of server names */
        protected $servers;
        /** @var bool */
        protected $automaticFailover;

        /**
         * Construct a RedisBagOStuff object. Parameters are:
         *
         *   - servers: An array of server names. A server name may be a hostname,
         *     a hostname/port combination or the absolute path of a UNIX socket.
         *     If a hostname is specified but no port, the standard port number
         *     6379 will be used. Required.
         *
         *   - connectTimeout: The timeout for new connections, in seconds. Optional,
         *     default is 1 second.
         *
         *   - persistent: Set this to true to allow connections to persist across
         *     multiple web requests. False by default.
         *
         *   - password: The authentication password, will be sent to Redis in
         *     clear text. Optional, if it is unspecified, no AUTH command will be
         *     sent.
         *
         *   - automaticFailover: If this is false, then each key will be mapped to
         *     a single server, and if that server is down, any requests for that key
         *     will fail. If this is true, a connection failure will cause the client
         *     to immediately try the next server in the list (as determined by a
         *     consistent hashing algorithm). True by default. This has the
         *     potential to create consistency issues if a server is slow enough to
         *     flap, for example if it is in swap death.
         */
        function __construct( $params ) {
                $redisConf = array( 'serializer' => 'none' ); // manage that in this class
                foreach ( array( 'connectTimeout', 'persistent', 'password' ) as $opt ) {
                        if ( isset( $params[$opt] ) ) {
                                $redisConf[$opt] = $params[$opt];
                        }
                }
                $this->redisPool = RedisConnectionPool::singleton( $redisConf );

                $this->servers = $params['servers'];
                if ( isset( $params['automaticFailover'] ) ) {
                        $this->automaticFailover = $params['automaticFailover'];
                } else {
                        $this->automaticFailover = true;
                }
        }

        public function get( $key, &$casToken = null ) {
                $section = new ProfileSection( __METHOD__ );

                list( $server, $conn ) = $this->getConnection( $key );
                if ( !$conn ) {
                        return false;
                }
                try {
                        $value = $conn->get( $key );
                        $casToken = $value;
                        $result = $this->unserialize( $value );
                } catch ( RedisException $e ) {
                        $result = false;
                        $this->handleException( $server, $conn, $e );
                }

                $this->logRequest( 'get', $key, $server, $result );
                return $result;
        }

        public function set( $key, $value, $expiry = 0 ) {
                $section = new ProfileSection( __METHOD__ );

                list( $server, $conn ) = $this->getConnection( $key );
                if ( !$conn ) {
                        return false;
                }
                $expiry = $this->convertToRelative( $expiry );
                try {
                        if ( $expiry ) {
                                $result = $conn->setex( $key, $expiry, $this->serialize( $value ) );
                        } else {
                                // No expiry, that is very different from zero expiry in Redis
                                $result = $conn->set( $key, $this->serialize( $value ) );
                        }
                } catch ( RedisException $e ) {
                        $result = false;
                        $this->handleException( $server, $conn, $e );
                }

                $this->logRequest( 'set', $key, $server, $result );
                return $result;
        }

        public function cas( $casToken, $key, $value, $expiry = 0 ) {
                $section = new ProfileSection( __METHOD__ );

                list( $server, $conn ) = $this->getConnection( $key );
                if ( !$conn ) {
                        return false;
                }
                $expiry = $this->convertToRelative( $expiry );
                try {
                        $conn->watch( $key );

                        if ( $this->serialize( $this->get( $key ) ) !== $casToken ) {
                                $conn->unwatch();
                                return false;
                        }

                        // multi()/exec() will fail atomically if the key changed since watch()
                        $conn->multi();
                        if ( $expiry ) {
                                $conn->setex( $key, $expiry, $this->serialize( $value ) );
                        } else {
                                // No expiry, that is very different from zero expiry in Redis
                                $conn->set( $key, $this->serialize( $value ) );
                        }
                        $result = ( $conn->exec() == array( true ) );
                } catch ( RedisException $e ) {
                        $result = false;
                        $this->handleException( $server, $conn, $e );
                }

                $this->logRequest( 'cas', $key, $server, $result );
                return $result;
        }

        public function delete( $key, $time = 0 ) {
                $section = new ProfileSection( __METHOD__ );

                list( $server, $conn ) = $this->getConnection( $key );
                if ( !$conn ) {
                        return false;
                }
                try {
                        $conn->delete( $key );
                        // Return true even if the key didn't exist
                        $result = true;
                } catch ( RedisException $e ) {
                        $result = false;
                        $this->handleException( $server, $conn, $e );
                }

                $this->logRequest( 'delete', $key, $server, $result );
                return $result;
        }

        public function getMulti( array $keys ) {
                $section = new ProfileSection( __METHOD__ );

                $batches = array();
                $conns = array();
                foreach ( $keys as $key ) {
                        list( $server, $conn ) = $this->getConnection( $key );
                        if ( !$conn ) {
                                continue;
                        }
                        $conns[$server] = $conn;
                        $batches[$server][] = $key;
                }
                $result = array();
                foreach ( $batches as $server => $batchKeys ) {
                        $conn = $conns[$server];
                        try {
                                $conn->multi( Redis::PIPELINE );
                                foreach ( $batchKeys as $key ) {
                                        $conn->get( $key );
                                }
                                $batchResult = $conn->exec();
                                if ( $batchResult === false ) {
                                        $this->debug( "multi request to $server failed" );
                                        continue;
                                }
                                foreach ( $batchResult as $i => $value ) {
                                        if ( $value !== false ) {
                                                $result[$batchKeys[$i]] = $this->unserialize( $value );
                                        }
                                }
                        } catch ( RedisException $e ) {
                                $this->handleException( $server, $conn, $e );
                        }
                }

                $this->debug( "getMulti for " . count( $keys ) . " keys " .
                        "returned " . count( $result ) . " results" );
                return $result;
        }

        public function add( $key, $value, $expiry = 0 ) {
                $section = new ProfileSection( __METHOD__ );

                list( $server, $conn ) = $this->getConnection( $key );
                if ( !$conn ) {
                        return false;
                }
                $expiry = $this->convertToRelative( $expiry );
                try {
                        if ( $expiry ) {
                                $conn->multi();
                                $conn->setnx( $key, $this->serialize( $value ) );
                                $conn->expire( $key, $expiry );
                                $result = ( $conn->exec() == array( true, true ) );
                        } else {
                                $result = $conn->setnx( $key, $this->serialize( $value ) );
                        }
                } catch ( RedisException $e ) {
                        $result = false;
                        $this->handleException( $server, $conn, $e );
                }

                $this->logRequest( 'add', $key, $server, $result );
                return $result;
        }

        /**
         * Non-atomic implementation of replace(). Could perhaps be done atomically
         * with WATCH or scripting, but this function is rarely used.
         */
        public function replace( $key, $value, $expiry = 0 ) {
                $section = new ProfileSection( __METHOD__ );

                list( $server, $conn ) = $this->getConnection( $key );
                if ( !$conn ) {
                        return false;
                }
                if ( !$conn->exists( $key ) ) {
                        return false;
                }

                $expiry = $this->convertToRelative( $expiry );
                try {
                        if ( !$expiry ) {
                                $result = $conn->set( $key, $this->serialize( $value ) );
                        } else {
                                $result = $conn->setex( $key, $expiry, $this->serialize( $value ) );
                        }
                } catch ( RedisException $e ) {
                        $result = false;
                        $this->handleException( $server, $conn, $e );
                }

                $this->logRequest( 'replace', $key, $server, $result );
                return $result;
        }

        /**
         * Non-atomic implementation of incr().
         *
         * Probably all callers actually want incr() to atomically initialise
         * values to zero if they don't exist, as provided by the Redis INCR
         * command. But we are constrained by the memcached-like interface to
         * return null in that case. Once the key exists, further increments are
         * atomic.
         */
        public function incr( $key, $value = 1 ) {
                $section = new ProfileSection( __METHOD__ );

                list( $server, $conn ) = $this->getConnection( $key );
                if ( !$conn ) {
                        return false;
                }
                if ( !$conn->exists( $key ) ) {
                        return null;
                }
                try {
                        $result = $this->unserialize( $conn->incrBy( $key, $value ) );
                } catch ( RedisException $e ) {
                        $result = false;
                        $this->handleException( $server, $conn, $e );
                }

                $this->logRequest( 'incr', $key, $server, $result );
                return $result;
        }

        /**
         * @param mixed $data
         * @return string
         */
        protected function serialize( $data ) {
                // Ignore digit strings and ints so INCR/DECR work
                return ( is_int( $data ) || ctype_digit( $data ) ) ? $data : serialize( $data );
        }

        /**
         * @param string $data
         * @return mixed
         */
        protected function unserialize( $data ) {
                // Ignore digit strings and ints so INCR/DECR work
                return ( is_int( $data ) || ctype_digit( $data ) ) ? $data : unserialize( $data );
        }

        /**
         * Get a Redis object with a connection suitable for fetching the specified key
         * @return Array (server, RedisConnRef) or (false, false)
         */
        protected function getConnection( $key ) {
                if ( count( $this->servers ) === 1 ) {
                        $candidates = $this->servers;
                } else {
                        $candidates = $this->servers;
                        ArrayUtils::consistentHashSort( $candidates, $key, '/' );
                        if ( !$this->automaticFailover ) {
                                $candidates = array_slice( $candidates, 0, 1 );
                        }
                }

                foreach ( $candidates as $server ) {
                        $conn = $this->redisPool->getConnection( $server );
                        if ( $conn ) {
                                return array( $server, $conn );
                        }
                }
                return array( false, false );
        }

        /**
         * Log a fatal error
         */
        protected function logError( $msg ) {
                wfDebugLog( 'redis', "Redis error: $msg\n" );
        }

        /**
         * The redis extension throws an exception in response to various read, write
         * and protocol errors. Sometimes it also closes the connection, sometimes
         * not. The safest response for us is to explicitly destroy the connection
         * object and let it be reopened during the next request.
         */
        protected function handleException( $server, RedisConnRef $conn, $e ) {
                $this->redisPool->handleException( $server, $conn, $e );
        }

        /**
         * Send information about a single request to the debug log
         */
        public function logRequest( $method, $key, $server, $result ) {
                $this->debug( "$method $key on $server: " .
                        ( $result === false ? "failure" : "success" ) );
        }
}