public function getLagTimes($serverIndexes, $wiki)
{
if (count($serverIndexes) == 1 && reset($serverIndexes) == 0) {
// Single server only, just return zero without caching
return array(0 => 0);
}
$expiry = 5;
$requestRate = 10;
$cache = $this->cache;
$masterName = $this->parent->getServerName(0);
$memcKey = wfMemcKey('lag_times', $masterName);
$times = $cache->get($memcKey);
if (is_array($times)) {
# Randomly recache with probability rising over $expiry
$elapsed = time() - $times['timestamp'];
$chance = max(0, ($expiry - $elapsed) * $requestRate);
if (mt_rand(0, $chance) != 0) {
unset($times['timestamp']);
// hide from caller
return $times;
}
wfIncrStats('lag_cache.miss.expired');
} else {
wfIncrStats('lag_cache.miss.absent');
}
# Cache key missing or expired
if ($cache->lock($memcKey, 0, 10)) {
# Let this process alone update the cache value
$unlocker = new ScopedCallback(function () use($cache, $memcKey) {
$cache->unlock($memcKey);
});
} elseif (is_array($times)) {
# Could not acquire lock but an old cache exists, so use it
unset($times['timestamp']);
// hide from caller
return $times;
}
$times = array();
foreach ($serverIndexes as $i) {
if ($i == 0) {
# Master
$times[$i] = 0;
} elseif (false !== ($conn = $this->parent->getAnyOpenConnection($i))) {
$times[$i] = $conn->getLag();
} elseif (false !== ($conn = $this->parent->openConnection($i, $wiki))) {
$times[$i] = $conn->getLag();
// 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
$times['timestamp'] = time();
$cache->set($memcKey, $times, $expiry + 10);
unset($times['timestamp']);
// hide from caller
return $times;
}
public function getLagTimes($serverIndexes, $wiki)
{
if (count($serverIndexes) == 1 && reset($serverIndexes) == 0) {
# Single server only, just return zero without caching
return array(0 => 0);
}
$key = $this->getLagTimeCacheKey();
# 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) - $ttl) {
wfDebugLog('replication', __METHOD__ . ": got lag times ({$key}) from local cache");
return $value['lagTimes'];
// 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, $staleTTL);
wfDebugLog('replication', __METHOD__ . ": got lag times ({$key}) from main cache");
return $value['lagTimes'];
// 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'];
}
$lagTimes = array();
foreach ($serverIndexes as $i) {
if ($i == 0) {
# Master
$lagTimes[$i] = 0;
} elseif (false !== ($conn = $this->parent->getAnyOpenConnection($i))) {
$lagTimes[$i] = $conn->getLag();
} elseif (false !== ($conn = $this->parent->openConnection($i, $wiki))) {
$lagTimes[$i] = $conn->getLag();
# 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 = array('lagTimes' => $lagTimes, 'timestamp' => microtime(true));
$this->mainCache->set($key, $value, $staleTTL);
$this->srvCache->set($key, $value, $staleTTL);
wfDebugLog('replication', __METHOD__ . ": re-calculated lag times ({$key})");
return $value['lagTimes'];
}
