64 $serverIndexes = array_keys( $weightByServer );
66 $coefficientsByServer = $states[
'weightScales'];
67 foreach ( $weightByServer
as $i => $weight ) {
68 if ( isset( $coefficientsByServer[$i] ) ) {
69 $weightByServer[$i] = $weight * $coefficientsByServer[$i];
71 $host = $this->parent->getServerName( $i );
72 $this->replLogger->error( __METHOD__ .
": host $host not in cache" );
84 $writerIndex = $this->parent->getWriterIndex();
85 if ( count( $serverIndexes ) == 1 && reset( $serverIndexes ) == $writerIndex ) {
86 # Single server only, just return zero without caching
88 'lagTimes' => [ $writerIndex => 0 ],
89 'weightScales' => [ $writerIndex => 1.0 ]
94 # Randomize TTLs to reduce stampedes (4.0 - 5.0 sec)
95 $ttl = mt_rand( 4e6, 5e6 ) / 1e6;
96 # Keep keys around longer as fallbacks
99 # (a) Check the local APC cache
100 $value = $this->srvCache->get( $key );
101 if (
$value &&
$value[
'timestamp'] > ( microtime(
true ) - $ttl ) ) {
102 $this->replLogger->debug( __METHOD__ .
": got lag times ($key) from local cache" );
105 $staleValue =
$value ?:
false;
107 # (b) Check the shared cache and backfill APC
108 $value = $this->mainCache->get( $key );
109 if (
$value &&
$value[
'timestamp'] > ( microtime(
true ) - $ttl ) ) {
110 $this->srvCache->set( $key,
$value, $staleTTL );
111 $this->replLogger->debug( __METHOD__ .
": got lag times ($key) from main cache" );
115 $staleValue =
$value ?: $staleValue;
117 # (c) Cache key missing or expired; regenerate and backfill
118 if ( $this->mainCache->lock( $key, 0, 10 ) ) {
119 # Let this process alone update the cache value
122 $unlocker =
new ScopedCallback(
function ()
use (
$cache, $key ) {
125 } elseif ( $staleValue ) {
126 # Could not acquire lock but an old cache exists, so use it
133 foreach ( $serverIndexes
as $i ) {
134 if ( $i == $this->parent->getWriterIndex() ) {
136 $weightScales[$i] = 1.0;
140 $conn = $this->parent->getAnyOpenConnection( $i );
144 $conn = $this->parent->openConnection( $i, $domain );
148 $lastWeight = isset( $staleValue[
'weightScales'][$i] )
149 ? $staleValue[
'weightScales'][$i]
152 $newWeight = $movAveRatio * $coefficient + ( 1 - $movAveRatio ) * $lastWeight;
155 $weightScales[$i] = max( $newWeight, .10 );
158 $lagTimes[$i] =
false;
159 $host = $this->parent->getServerName( $i );
160 $this->replLogger->error( __METHOD__ .
": host $host is unreachable" );
164 if ( $conn->getLBInfo(
'is static' ) ) {
167 $lagTimes[$i] = $conn->getLag();
168 if ( $lagTimes[$i] ===
false ) {
169 $host = $this->parent->getServerName( $i );
170 $this->replLogger->error( __METHOD__ .
": host $host is not replicating?" );
175 # Close the connection to avoid sleeper connections piling up.
176 # Note that the caller will pick one of these DBs and reconnect,
177 # which is slightly inefficient, but this only matters for the lag
178 # time cache miss cache, which is far less common that cache hits.
179 $this->parent->closeConnection( $conn );
183 # Add a timestamp key so we know when it was cached
185 'lagTimes' => $lagTimes,
186 'weightScales' => $weightScales,
187 'timestamp' => microtime(
true )
189 $this->mainCache->set( $key,
$value, $staleTTL );
190 $this->srvCache->set( $key,
$value, $staleTTL );
191 $this->replLogger->info( __METHOD__ .
": re-calculated lag times ($key)" );