protected function getServerStates(array $serverIndexes, $domain)
{
$writerIndex = $this->parent->getWriterIndex();
if (count($serverIndexes) == 1 && reset($serverIndexes) == $writerIndex) {
# Single server only, just return zero without caching
return ['lagTimes' => [$writerIndex => 0], 'weightScales' => [$writerIndex => 1.0]];
}
$key = $this->getCacheKey($serverIndexes);
# Randomize TTLs to reduce stampedes (4.0 - 5.0 sec)
$ttl = mt_rand(4000000.0, 5000000.0) / 1000000.0;
# Keep keys around longer as fallbacks
$staleTTL = 60;
# (a) Check the local APC cache
$value = $this->srvCache->get($key);
if ($value && $value['timestamp'] > microtime(true) - $ttl) {
$this->replLogger->debug(__METHOD__ . ": got lag times ({$key}) from local cache");
return $value;
// cache hit
}
$staleValue = $value ?: false;
# (b) Check the shared cache and backfill APC
$value = $this->mainCache->get($key);
if ($value && $value['timestamp'] > microtime(true) - $ttl) {
$this->srvCache->set($key, $value, $staleTTL);
$this->replLogger->debug(__METHOD__ . ": got lag times ({$key}) from main cache");
return $value;
// cache hit
}
$staleValue = $value ?: $staleValue;
# (c) Cache key missing or expired; regenerate and backfill
if ($this->mainCache->lock($key, 0, 10)) {
# Let this process alone update the cache value
$cache = $this->mainCache;
/** @noinspection PhpUnusedLocalVariableInspection */
$unlocker = new ScopedCallback(function () use($cache, $key) {
$cache->unlock($key);
});
} elseif ($staleValue) {
# Could not acquire lock but an old cache exists, so use it
return $staleValue;
}
$lagTimes = [];
$weightScales = [];
$movAveRatio = $this->movingAveRatio;
foreach ($serverIndexes as $i) {
if ($i == $this->parent->getWriterIndex()) {
$lagTimes[$i] = 0;
// master always has no lag
$weightScales[$i] = 1.0;
// nominal weight
continue;
}
$conn = $this->parent->getAnyOpenConnection($i);
if ($conn) {
$close = false;
// already open
} else {
$conn = $this->parent->openConnection($i, $domain);
$close = true;
// new connection
}
$lastWeight = isset($staleValue['weightScales'][$i]) ? $staleValue['weightScales'][$i] : 1.0;
$coefficient = $this->getWeightScale($i, $conn ?: null);
$newWeight = $movAveRatio * $coefficient + (1 - $movAveRatio) * $lastWeight;
// Scale from 10% to 100% of nominal weight
$weightScales[$i] = max($newWeight, 0.1);
if (!$conn) {
$lagTimes[$i] = false;
$host = $this->parent->getServerName($i);
$this->replLogger->error(__METHOD__ . ": host {$host} is unreachable");
continue;
}
if ($conn->getLBInfo('is static')) {
$lagTimes[$i] = 0;
} else {
$lagTimes[$i] = $conn->getLag();
if ($lagTimes[$i] === false) {
$host = $this->parent->getServerName($i);
$this->replLogger->error(__METHOD__ . ": host {$host} is not replicating?");
}
}
if ($close) {
# Close the connection to avoid sleeper connections piling up.
# Note that the caller will pick one of these DBs and reconnect,
# which is slightly inefficient, but this only matters for the lag
# time cache miss cache, which is far less common that cache hits.
$this->parent->closeConnection($conn);
}
}
# Add a timestamp key so we know when it was cached
$value = ['lagTimes' => $lagTimes, 'weightScales' => $weightScales, 'timestamp' => microtime(true)];
$this->mainCache->set($key, $value, $staleTTL);
$this->srvCache->set($key, $value, $staleTTL);
$this->replLogger->info(__METHOD__ . ": re-calculated lag times ({$key})");
return $value;
}
