3 * Database load monitoring.
5 * This program is free software; you can redistribute it and/or modify
6 * it under the terms of the GNU General Public License as published by
7 * the Free Software Foundation; either version 2 of the License, or
8 * (at your option) any later version.
10 * This program is distributed in the hope that it will be useful,
11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 * GNU General Public License for more details.
15 * You should have received a copy of the GNU General Public License along
16 * with this program; if not, write to the Free Software Foundation, Inc.,
17 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
18 * http://www.gnu.org/copyleft/gpl.html
25 * An interface for database load monitoring
29 interface LoadMonitor
{
31 * Construct a new LoadMonitor with a given LoadBalancer parent
33 * @param LoadBalancer $parent
35 function __construct( $parent );
38 * Perform pre-connection load ratio adjustment.
40 * @param string|bool $group The selected query group. Default: false
41 * @param string|bool $wiki Default: false
43 function scaleLoads( &$loads, $group = false, $wiki = false );
46 * Return an estimate of replication lag for each server
48 * @param array $serverIndexes
53 function getLagTimes( $serverIndexes, $wiki );
56 class LoadMonitorNull
implements LoadMonitor
{
57 function __construct( $parent ) {
60 function scaleLoads( &$loads, $group = false, $wiki = false ) {
64 * @param array $serverIndexes
68 function getLagTimes( $serverIndexes, $wiki ) {
69 return array_fill_keys( $serverIndexes, 0 );
74 * Basic MySQL load monitor with no external dependencies
75 * Uses memcached to cache the replication lag for a short time
79 class LoadMonitorMySQL
implements LoadMonitor
{
80 /** @var LoadBalancer */
84 * @param LoadBalancer $parent
86 function __construct( $parent ) {
87 $this->parent
= $parent;
95 function scaleLoads( &$loads, $group = false, $wiki = false ) {
99 * @param array $serverIndexes
100 * @param string $wiki
103 function getLagTimes( $serverIndexes, $wiki ) {
104 if ( count( $serverIndexes ) == 1 && reset( $serverIndexes ) == 0 ) {
105 // Single server only, just return zero without caching
106 return array( 0 => 0 );
109 wfProfileIn( __METHOD__
);
114 if ( empty( $wgMemc ) ) {
115 $wgMemc = wfGetMainCache();
118 $masterName = $this->parent
->getServerName( 0 );
119 $memcKey = wfMemcKey( 'lag_times', $masterName );
120 $times = $wgMemc->get( $memcKey );
121 if ( is_array( $times ) ) {
122 # Randomly recache with probability rising over $expiry
123 $elapsed = time() - $times['timestamp'];
124 $chance = max( 0, ( $expiry - $elapsed ) * $requestRate );
125 if ( mt_rand( 0, $chance ) != 0 ) {
126 unset( $times['timestamp'] ); // hide from caller
127 wfProfileOut( __METHOD__
);
131 wfIncrStats( 'lag_cache_miss_expired' );
133 wfIncrStats( 'lag_cache_miss_absent' );
136 # Cache key missing or expired
137 if ( $wgMemc->add( "$memcKey:lock", 1, 10 ) ) {
138 # Let this process alone update the cache value
139 $unlocker = new ScopedCallback( function () use ( $wgMemc, $memcKey ) {
140 $wgMemc->delete( $memcKey );
142 } elseif ( is_array( $times ) ) {
143 # Could not acquire lock but an old cache exists, so use it
144 unset( $times['timestamp'] ); // hide from caller
145 wfProfileOut( __METHOD__
);
151 foreach ( $serverIndexes as $i ) {
152 if ( $i == 0 ) { # Master
154 } elseif ( false !== ( $conn = $this->parent
->getAnyOpenConnection( $i ) ) ) {
155 $times[$i] = $conn->getLag();
156 } elseif ( false !== ( $conn = $this->parent
->openConnection( $i, $wiki ) ) ) {
157 $times[$i] = $conn->getLag();
161 # Add a timestamp key so we know when it was cached
162 $times['timestamp'] = time();
163 $wgMemc->set( $memcKey, $times, $expiry +
10 );
164 unset( $times['timestamp'] ); // hide from caller
166 wfProfileOut( __METHOD__
);