*
* ### Deploying WANObjectCache
*
- * There are three supported ways to set up broadcasted operations:
+ * There are two supported ways to set up broadcasted operations:
*
- * - A) Configure the 'purge' EventRelayer to point to a valid PubSub endpoint
- * that has subscribed listeners on the cache servers applying the cache updates.
- * - B) Omit the 'purge' EventRelayer parameter and set up mcrouter as the underlying cache
- * backend, using a memcached BagOStuff class for the 'cache' parameter. The 'region'
- * and 'cluster' parameters must be provided and 'mcrouterAware' must be set to `true`.
+ * - A) Set up mcrouter as the underlying cache backend, using a memcached BagOStuff class
+ * for the 'cache' parameter. The 'region' and 'cluster' parameters must be provided
+ * and 'mcrouterAware' must be set to `true`.
* Configure mcrouter as follows:
* - 1) Use Route Prefixing based on region (datacenter) and cache cluster.
* See https://github.com/facebook/mcrouter/wiki/Routing-Prefix and
* configure 'set' and 'delete' operations to go to all servers in the cache
* cluster, instead of just one server determined by hashing.
* See https://github.com/facebook/mcrouter/wiki/List-of-Route-Handles.
- * - C) Omit the 'purge' EventRelayer parameter and set up dynomite as cache middleware
- * between the web servers and either memcached or redis. This will broadcast all
- * key setting operations, not just purges, which can be useful for cache warming.
- * Writes are eventually consistent via the Dynamo replication model.
- * See https://github.com/Netflix/dynomite.
+ * - B) Set up dynomite as a cache middleware between the web servers and either memcached
+ * or redis and use it as the underlying cache backend, using a memcached BagOStuff
+ * class for the 'cache' parameter. This will broadcast all key setting operations,
+ * not just purges, which can be useful for cache warming. Writes are eventually
+ * consistent via the Dynamo replication model. See https://github.com/Netflix/dynomite.
*
* Broadcasted operations like delete() and touchCheckKey() are done asynchronously
* in all datacenters this way, though the local one should likely be near immediate.
protected $cache;
/** @var MapCacheLRU[] Map of group PHP instance caches */
protected $processCaches = [];
- /** @var string Purge channel name */
- protected $purgeChannel;
- /** @var EventRelayer Bus that handles purge broadcasts */
- protected $purgeRelayer;
/** @bar bool Whether to use mcrouter key prefixing for routing */
protected $mcrouterAware;
/** @var string Physical region for mcrouter use */
/** @var float Unix timestamp of the oldest possible valid values */
protected $epoch;
- /** @var int ERR_* constant for the "last error" registry */
- protected $lastRelayError = self::ERR_NONE;
-
/** @var int Callback stack depth for getWithSetCallback() */
private $callbackDepth = 0;
/** @var mixed[] Temporary warm-up cache */
/**
* @param array $params
* - cache : BagOStuff object for a persistent cache
- * - channels : Map of (action => channel string). Actions include "purge".
- * - relayers : Map of (action => EventRelayer object). Actions include "purge".
* - logger : LoggerInterface object
* - stats : LoggerInterface object
* - asyncHandler : A function that takes a callback and runs it later. If supplied,
*/
public function __construct( array $params ) {
$this->cache = $params['cache'];
- $this->purgeChannel = $params['channels']['purge'] ?? self::DEFAULT_PURGE_CHANNEL;
- $this->purgeRelayer = $params['relayers']['purge'] ?? new EventRelayerNull( [] );
$this->region = $params['region'] ?? 'main';
$this->cluster = $params['cluster'] ?? 'wan-main';
$this->mcrouterAware = !empty( $params['mcrouterAware'] );
$preCallbackTime = $this->getCurrentTime();
// Determine if a cached value regeneration is needed or desired
- if ( $value !== false
- && $this->isAliveOrInGracePeriod( $curTTL, $graceTTL )
- && $this->isValid( $value, $versioned, $asOf, $minTime )
+ if (
+ $this->isValid( $value, $versioned, $asOf, $minTime ) &&
+ $this->isAliveOrInGracePeriod( $curTTL, $graceTTL )
) {
$preemptiveRefresh = (
$this->worthRefreshExpiring( $curTTL, $lowTTL ) ||
}
}
- // A deleted key with a negative TTL left must be tombstoned
- $isTombstone = ( $curTTL !== null && $value === false );
- if ( $isTombstone && $lockTSE <= 0 ) {
- // Use the INTERIM value for tombstoned keys to reduce regeneration load
- $lockTSE = self::INTERIM_KEY_TTL;
- }
- // Assume a key is hot if requested soon after invalidation
- $isHot = ( $curTTL !== null && $curTTL <= 0 && abs( $curTTL ) <= $lockTSE );
- // Use the mutex if there is no value and a busy fallback is given
- $checkBusy = ( $busyValue !== null && $value === false );
- // Decide whether a single thread should handle regenerations.
- // This avoids stampedes when $checkKeys are bumped and when preemptive
- // renegerations take too long. It also reduces regenerations while $key
- // is tombstoned. This balances cache freshness with avoiding DB load.
- $useMutex = ( $isHot || ( $isTombstone && $lockTSE > 0 ) || $checkBusy );
+ // Only a tombstoned key yields no value yet has a (negative) "current time left"
+ $isKeyTombstoned = ( $curTTL !== null && $value === false );
+ // Decide if only one thread should handle regeneration at a time
+ $useMutex =
+ // Note that since tombstones no-op set(), $lockTSE and $curTTL cannot be used to
+ // deduce the key hotness because $curTTL will always keep increasing until the
+ // tombstone expires or is overwritten by a new tombstone. Also, even if $lockTSE
+ // is not set, constant regeneration of a key for the tombstone lifetime might be
+ // very expensive. Assume tombstoned keys are possibly hot in order to reduce
+ // the risk of high regeneration load after the delete() method is called.
+ $isKeyTombstoned ||
+ // Assume a key is hot if requested soon ($lockTSE seconds) after invalidation.
+ // This avoids stampedes when timestamps from $checkKeys/$touchedCallback bump.
+ ( $curTTL !== null && $curTTL <= 0 && abs( $curTTL ) <= $lockTSE ) ||
+ // Assume a key is hot if there is no value and a busy fallback is given.
+ // This avoids stampedes on eviction or preemptive regeneration taking too long.
+ ( $busyValue !== null && $value === false );
$lockAcquired = false;
if ( $useMutex ) {
// Acquire a datacenter-local non-blocking lock
if ( $this->cache->add( self::MUTEX_KEY_PREFIX . $key, 1, self::LOCK_TTL ) ) {
- // Lock acquired; this thread should update the key
+ // Lock acquired; this thread will recompute the value and update cache
$lockAcquired = true;
- } elseif ( $value !== false && $this->isValid( $value, $versioned, $asOf, $minTime ) ) {
+ } elseif ( $this->isValid( $value, $versioned, $asOf, $minTime ) ) {
+ // Lock not acquired and a stale value exists; use the stale value
$this->stats->increment( "wanobjectcache.$kClass.hit.stale" );
- // If it cannot be acquired; then the stale value can be used
+
return $value;
} else {
- // Use the INTERIM value for tombstoned keys to reduce regeneration load.
- // For hot keys, either another thread has the lock or the lock failed;
- // use the INTERIM value from the last thread that regenerated it.
- $value = $this->getInterimValue( $key, $versioned, $minTime, $asOf );
- if ( $value !== false ) {
- $this->stats->increment( "wanobjectcache.$kClass.hit.volatile" );
-
- return $value;
+ // Lock not acquired and no stale value exists
+ if ( $isKeyTombstoned ) {
+ // Use the INTERIM value from the last thread that regenerated it if possible
+ $value = $this->getInterimValue( $key, $versioned, $minTime, $asOf );
+ if ( $value !== false ) {
+ $this->stats->increment( "wanobjectcache.$kClass.hit.volatile" );
+
+ return $value;
+ }
}
- // Use the busy fallback value if nothing else
+
if ( $busyValue !== null ) {
+ // Use the busy fallback value if nothing else
$miss = is_infinite( $minTime ) ? 'renew' : 'miss';
$this->stats->increment( "wanobjectcache.$kClass.$miss.busy" );
}
$valueIsCacheable = ( $value !== false && $ttl >= 0 );
- // When delete() is called, writes are write-holed by the tombstone,
- // so use a special INTERIM key to pass the new value around threads.
- if ( ( $isTombstone && $lockTSE > 0 ) && $valueIsCacheable ) {
- $tempTTL = max( 1, (int)$lockTSE ); // set() expects seconds
- $newAsOf = $this->getCurrentTime();
- $wrapped = $this->wrap( $value, $tempTTL, $newAsOf );
- // Avoid using set() to avoid pointless mcrouter broadcasting
- $this->setInterimValue( $key, $wrapped, $tempTTL );
- }
-
- // Save the value unless a mutex-winning thread is already expected to do that
- if ( $valueIsCacheable && ( !$useMutex || $lockAcquired ) ) {
- $setOpts['lockTSE'] = $lockTSE;
- $setOpts['staleTTL'] = $staleTTL;
- // Use best known "since" timestamp if not provided
- $setOpts += [ 'since' => $preCallbackTime ];
- // Update the cache; this will fail if the key is tombstoned
- $this->set( $key, $value, $ttl, $setOpts );
+ if ( $valueIsCacheable ) {
+ if ( $isKeyTombstoned ) {
+ // When delete() is called, writes are write-holed by the tombstone,
+ // so use a special INTERIM key to pass the new value among threads.
+ $tempTTL = max( self::INTERIM_KEY_TTL, (int)$lockTSE ); // set() expects seconds
+ $newAsOf = $this->getCurrentTime();
+ $wrapped = $this->wrap( $value, $tempTTL, $newAsOf );
+ // Avoid using set() to avoid pointless mcrouter broadcasting
+ $this->setInterimValue( $key, $wrapped, $tempTTL );
+ } elseif ( !$useMutex || $lockAcquired ) {
+ // Save the value unless a lock-winning thread is already expected to do that
+ $setOpts['lockTSE'] = $lockTSE;
+ $setOpts['staleTTL'] = $staleTTL;
+ // Use best known "since" timestamp if not provided
+ $setOpts += [ 'since' => $preCallbackTime ];
+ // Update the cache; this will fail if the key is tombstoned
+ $this->set( $key, $value, $ttl, $setOpts );
+ }
}
if ( $lockAcquired ) {
$wrapped = $this->cache->get( self::INTERIM_KEY_PREFIX . $key );
list( $value ) = $this->unwrap( $wrapped, $this->getCurrentTime() );
- if ( $value !== false && $this->isValid( $value, $versioned, $asOf, $minTime ) ) {
+ if ( $this->isValid( $value, $versioned, $asOf, $minTime ) ) {
$asOf = $wrapped[self::FLD_TIME];
return $value;
* @return int ERR_* class constant for the "last error" registry
*/
final public function getLastError() {
- if ( $this->lastRelayError ) {
- // If the cache and the relayer failed, focus on the latter.
- // An update not making it to the relayer means it won't show up
- // in other DCs (nor will consistent re-hashing see up-to-date values).
- // On the other hand, if just the cache update failed, then it should
- // eventually be applied by the relayer.
- return $this->lastRelayError;
- }
-
$code = $this->cache->getLastError();
switch ( $code ) {
case BagOStuff::ERR_NONE:
*/
final public function clearLastError() {
$this->cache->clearLastError();
- $this->lastRelayError = self::ERR_NONE;
}
/**
$this->makePurgeValue( $this->getCurrentTime(), self::HOLDOFF_NONE ),
$ttl
);
- } elseif ( $this->purgeRelayer instanceof EventRelayerNull ) {
+ } else {
// This handles the mcrouter and the single-DC case
$ok = $this->cache->set(
$key,
$this->makePurgeValue( $this->getCurrentTime(), self::HOLDOFF_NONE ),
$ttl
);
- } else {
- $event = $this->cache->modifySimpleRelayEvent( [
- 'cmd' => 'set',
- 'key' => $key,
- 'val' => 'PURGED:$UNIXTIME$:' . (int)$holdoff,
- 'ttl' => max( $ttl, self::TTL_SECOND ),
- 'sbt' => true, // substitute $UNIXTIME$ with actual microtime
- ] );
-
- $ok = $this->purgeRelayer->notify( $this->purgeChannel, $event );
- if ( !$ok ) {
- $this->lastRelayError = self::ERR_RELAY;
- }
}
return $ok;
// See https://github.com/facebook/mcrouter/wiki/Multi-cluster-broadcast-setup
// Wildcards select all matching routes, e.g. the WAN cluster on all DCs
$ok = $this->cache->delete( "/*/{$this->cluster}/{$key}" );
- } elseif ( $this->purgeRelayer instanceof EventRelayerNull ) {
+ } else {
// Some other proxy handles broadcasting or there is only one datacenter
$ok = $this->cache->delete( $key );
- } else {
- $event = $this->cache->modifySimpleRelayEvent( [
- 'cmd' => 'delete',
- 'key' => $key,
- ] );
-
- $ok = $this->purgeRelayer->notify( $this->purgeChannel, $event );
- if ( !$ok ) {
- $this->lastRelayError = self::ERR_RELAY;
- }
}
return $ok;
}
/**
- * Check whether $value is appropriately versioned and not older than $minTime (if set)
+ * Check if $value is not false, versioned (if needed), and not older than $minTime (if set)
*
- * @param array $value
+ * @param array|bool $value
* @param bool $versioned
* @param float $asOf The time $value was generated
* @param float $minTime The last time the main value was generated (0.0 if unknown)
* @return bool
*/
protected function isValid( $value, $versioned, $asOf, $minTime ) {
- if ( $versioned && !isset( $value[self::VFLD_VERSION] ) ) {
+ if ( $value === false ) {
+ return false;
+ } elseif ( $versioned && !isset( $value[self::VFLD_VERSION] ) ) {
return false;
} elseif ( $minTime > 0 && $asOf < $minTime ) {
return false;
dépôts / lhc / web / wiklou.git / blobdiff