* @author Aaron Schulz
*/
+use Psr\Log\LoggerAwareInterface;
+use Psr\Log\LoggerInterface;
+use Psr\Log\NullLogger;
+
/**
* Multi-datacenter aware caching interface
*
* @ingroup Cache
* @since 1.26
*/
-class WANObjectCache {
+class WANObjectCache implements IExpiringStore, LoggerAwareInterface {
/** @var BagOStuff The local datacenter cache */
protected $cache;
/** @var HashBagOStuff Script instance PHP cache */
protected $pool;
/** @var EventRelayer Bus that handles purge broadcasts */
protected $relayer;
+ /** @var LoggerInterface */
+ protected $logger;
/** @var int ERR_* constant for the "last error" registry */
protected $lastRelayError = self::ERR_NONE;
/** Max time expected to pass between delete() and DB commit finishing */
const MAX_COMMIT_DELAY = 3;
- /** Max replication lag before applying TTL_LAGGED to set() */
- const MAX_REPLICA_LAG = 5;
- /** Max time since snapshot transaction start to avoid no-op of set() */
- const MAX_SNAPSHOT_LAG = 5;
+ /** Max replication+snapshot lag before applying TTL_LAGGED or disallowing set() */
+ const MAX_READ_LAG = 7;
/** Seconds to tombstone keys on delete() */
- const HOLDOFF_TTL = 14; // MAX_COMMIT_DELAY + MAX_REPLICA_LAG + MAX_SNAPSHOT_LAG + 1
+ const HOLDOFF_TTL = 11; // MAX_COMMIT_DELAY + MAX_READ_LAG + 1
/** Seconds to keep dependency purge keys around */
- const CHECK_KEY_TTL = 31536000; // 1 year
+ const CHECK_KEY_TTL = self::TTL_YEAR;
/** Seconds to keep lock keys around */
- const LOCK_TTL = 5;
+ const LOCK_TTL = 10;
/** Default remaining TTL at which to consider pre-emptive regeneration */
const LOW_TTL = 30;
/** Default time-since-expiry on a miss that makes a key "hot" */
const LOCK_TSE = 1;
- /** Idiom for set()/getWithSetCallback() TTL being "forever" */
- const TTL_NONE = 0;
/** Idiom for getWithSetCallback() callbacks to avoid calling set() */
const TTL_UNCACHEABLE = -1;
/** Idiom for getWithSetCallback() callbacks to 'lockTSE' logic */
/** Max TTL to store keys when a data sourced is lagged */
const TTL_LAGGED = 30;
+ /** Tiny negative float to use when CTL comes up >= 0 due to clock skew */
+ const TINY_NEGATIVE = -0.000001;
+
/** Cache format version number */
const VERSION = 1;
const FLD_VALUE = 1;
const FLD_TTL = 2;
const FLD_TIME = 3;
+ const FLD_FLAGS = 4;
+
+ /** @var integer Treat this value as expired-on-arrival */
+ const FLG_STALE = 1;
const ERR_NONE = 0; // no error
const ERR_NO_RESPONSE = 1; // no response
const PURGE_VAL_PREFIX = 'PURGED:';
+ const MAX_PC_KEYS = 1000; // max keys to keep in process cache
+
/**
* @param array $params
* - cache : BagOStuff object
* - pool : pool name
* - relayer : EventRelayer object
+ * - logger : LoggerInterface object
*/
public function __construct( array $params ) {
$this->cache = $params['cache'];
$this->pool = $params['pool'];
$this->relayer = $params['relayer'];
- $this->procCache = new HashBagOStuff();
+ $this->procCache = new HashBagOStuff( array( 'maxKeys' => self::MAX_PC_KEYS ) );
+ $this->setLogger( isset( $params['logger'] ) ? $params['logger'] : new NullLogger() );
+ }
+
+ public function setLogger( LoggerInterface $logger ) {
+ $this->logger = $logger;
}
/**
/**
* Fetch the value of a key from cache
*
- * If passed in, $curTTL is set to the remaining TTL (current time left):
- * - a) INF; if the key exists, has no TTL, and is not expired by $checkKeys
- * - b) float (>=0); if the key exists, has a TTL, and is not expired by $checkKeys
- * - c) float (<0); if the key is tombstoned or existing but expired by $checkKeys
- * - d) null; if the key does not exist and is not tombstoned
+ * If supplied, $curTTL is set to the remaining TTL (current time left):
+ * - a) INF; if $key exists, has no TTL, and is not expired by $checkKeys
+ * - b) float (>=0); if $key exists, has a TTL, and is not expired by $checkKeys
+ * - c) float (<0); if $key is tombstoned, stale, or existing but expired by $checkKeys
+ * - d) null; if $key does not exist and is not tombstoned
*
* If a key is tombstoned, $curTTL will reflect the time since delete().
*
* $setOpts = Database::getCacheSetOptions( $dbr );
* // Fetch the row from the DB
* $row = $dbr->selectRow( ... );
- * $key = wfMemcKey( 'building', $buildingId );
- * $cache->set( $key, $row, 86400, $setOpts );
+ * $key = $cache->makeKey( 'building', $buildingId );
+ * $cache->set( $key, $row, $cache::TTL_DAY, $setOpts );
* @endcode
*
* @param string $key Cache key
* @param mixed $value
- * @param integer $ttl Seconds to live [0=forever]
+ * @param integer $ttl Seconds to live. Special values are:
+ * - WANObjectCache::TTL_INDEFINITE: Cache forever
* @param array $opts Options map:
* - lag : Seconds of slave lag. Typically, this is either the slave lag
* before the data was read or, if applicable, the slave lag before
* the current time the data was read or (if applicable) the time when
* the snapshot-isolated transaction the data was read from started.
* Default: 0 seconds
- * - lockTSE : if excessive possible snapshot lag is detected,
- * then stash the value into a temporary location
- * with this TTL. This is only useful if the reads
- * use getWithSetCallback() with "lockTSE" set.
+ * - pending : Whether this data is possibly from an uncommitted write transaction.
+ * Generally, other threads should not see values from the future and
+ * they certainly should not see ones that ended up getting rolled back.
+ * Default: false
+ * - lockTSE : if excessive replication/snapshot lag is detected, then store the value
+ * with this TTL and flag it as stale. This is only useful if the reads for
+ * this key use getWithSetCallback() with "lockTSE" set.
* Default: WANObjectCache::TSE_NONE
* @return bool Success
*/
$age = isset( $opts['since'] ) ? max( 0, microtime( true ) - $opts['since'] ) : 0;
$lag = isset( $opts['lag'] ) ? $opts['lag'] : 0;
- if ( $lag > self::MAX_REPLICA_LAG ) {
- // Too much lag detected; lower TTL so it converges faster
- $ttl = $ttl ? min( $ttl, self::TTL_LAGGED ) : self::TTL_LAGGED;
+ // Do not cache potentially uncommitted data as it might get rolled back
+ if ( !empty( $opts['pending'] ) ) {
+ $this->logger->info( "Rejected set() for $key due to pending writes." );
+
+ return true; // no-op the write for being unsafe
}
- if ( $age > self::MAX_SNAPSHOT_LAG ) {
+ $wrapExtra = array(); // additional wrapped value fields
+ // Check if there's a risk of writing stale data after the purge tombstone expired
+ if ( ( $lag + $age ) > self::MAX_READ_LAG ) {
+ // Case A: read lag with "lockTSE"; save but record value as stale
if ( $lockTSE >= 0 ) {
- $tempTTL = max( 1, (int)$lockTSE ); // set() expects seconds
- $this->cache->set( self::STASH_KEY_PREFIX . $key, $value, $tempTTL );
- }
+ $ttl = max( 1, (int)$lockTSE ); // set() expects seconds
+ $wrapExtra[self::FLD_FLAGS] = self::FLG_STALE; // mark as stale
+ // Case B: any long-running transaction; ignore this set()
+ } elseif ( $age > self::MAX_READ_LAG ) {
+ $this->logger->warning( "Rejected set() for $key due to snapshot lag." );
+
+ return true; // no-op the write for being unsafe
+ // Case C: high replication lag; lower TTL instead of ignoring all set()s
+ } elseif ( $lag > self::MAX_READ_LAG ) {
+ $ttl = $ttl ? min( $ttl, self::TTL_LAGGED ) : self::TTL_LAGGED;
+ $this->logger->warning( "Lowered set() TTL for $key due to replication lag." );
+ // Case D: medium length request with medium replication lag; ignore this set()
+ } else {
+ $this->logger->warning( "Rejected set() for $key due to high read lag." );
- return true; // no-op the write for being unsafe
+ return true; // no-op the write for being unsafe
+ }
}
- $wrapped = $this->wrap( $value, $ttl );
+ // Wrap that value with time/TTL/version metadata
+ $wrapped = $this->wrap( $value, $ttl ) + $wrapExtra;
$func = function ( $cache, $key, $cWrapped ) use ( $wrapped ) {
return ( is_string( $cWrapped ) )
* ... <execute some stuff> ...
* // Update the row in the DB
* $dbw->update( ... );
- * $key = wfMemcKey( 'homes', $homeId );
+ * $key = $cache->makeKey( 'homes', $homeId );
* // Purge the corresponding cache entry just before committing
* $dbw->onTransactionPreCommitOrIdle( function() use ( $cache, $key ) {
* $cache->delete( $key );
* $dbw->commit(); // end of request
* @endcode
*
- * If called twice on the same key, then the last hold-off TTL takes
- * precedence. For idempotence, the $ttl should not vary for different
- * delete() calls on the same key. Also note that lowering $ttl reduces
- * the effective range of the 'lockTSE' parameter to getWithSetCallback().
+ * The $ttl parameter can be used when purging values that have not actually changed
+ * recently. For example, a cleanup script to purge cache entries does not really need
+ * a hold-off period, so it can use the value 1. Likewise for user-requested purge.
+ * Note that $ttl limits the effective range of 'lockTSE' for getWithSetCallback().
+ *
+ * If called twice on the same key, then the last hold-off TTL takes precedence. For
+ * idempotence, the $ttl should not vary for different delete() calls on the same key.
*
* @param string $key Cache key
- * @param integer $ttl How long to block writes to the key [seconds]
+ * @param integer $ttl Tombstone TTL; Default: WANObjectCache::HOLDOFF_TTL
* @return bool True if the item was purged or not found, false on failure
*/
final public function delete( $key, $ttl = self::HOLDOFF_TTL ) {
* @code
* $catInfo = $cache->getWithSetCallback(
* // Key to store the cached value under
- * wfMemcKey( 'cat-attributes', $catId ),
- * // Time-to-live (seconds)
- * 60,
+ * $cache->makeKey( 'cat-attributes', $catId ),
+ * // Time-to-live (in seconds)
+ * $cache::TTL_MINUTE,
* // Function that derives the new key value
* function ( $oldValue, &$ttl, array &$setOpts ) {
* $dbr = wfGetDB( DB_SLAVE );
* @code
* $catConfig = $cache->getWithSetCallback(
* // Key to store the cached value under
- * wfMemcKey( 'site-cat-config' ),
- * // Time-to-live (seconds)
- * 86400,
+ * $cache->makeKey( 'site-cat-config' ),
+ * // Time-to-live (in seconds)
+ * $cache::TTL_DAY,
* // Function that derives the new key value
* function ( $oldValue, &$ttl, array &$setOpts ) {
* $dbr = wfGetDB( DB_SLAVE );
* },
* array(
* // Calling touchCheckKey() on this key invalidates the cache
- * 'checkKeys' => array( wfMemcKey( 'site-cat-config' ) ),
+ * 'checkKeys' => array( $cache->makeKey( 'site-cat-config' ) ),
* // Try to only let one datacenter thread manage cache updates at a time
* 'lockTSE' => 30
* )
* @code
* $catState = $cache->getWithSetCallback(
* // Key to store the cached value under
- * wfMemcKey( 'cat-state', $cat->getId() ),
+ * $cache->makeKey( 'cat-state', $cat->getId() ),
* // Time-to-live (seconds)
- * 900,
+ * $cache::TTL_HOUR,
* // Function that derives the new key value
* function ( $oldValue, &$ttl, array &$setOpts ) {
* // Determine new value from the DB
* // The "check" keys that represent things the value depends on;
* // Calling touchCheckKey() on any of them invalidates the cache
* 'checkKeys' => array(
- * wfMemcKey( 'sustenance-bowls', $cat->getRoomId() ),
- * wfMemcKey( 'people-present', $cat->getHouseId() ),
- * wfMemcKey( 'cat-laws', $cat->getCityId() ),
+ * $cache->makeKey( 'sustenance-bowls', $cat->getRoomId() ),
+ * $cache->makeKey( 'people-present', $cat->getHouseId() ),
+ * $cache->makeKey( 'cat-laws', $cat->getCityId() ),
* )
* )
* );
* @code
* $lastCatActions = $cache->getWithSetCallback(
* // Key to store the cached value under
- * wfMemcKey( 'cat-last-actions', 100 ),
- * // Time-to-live (seconds)
+ * $cache->makeKey( 'cat-last-actions', 100 ),
+ * // Time-to-live (in seconds)
* 10,
* // Function that derives the new key value
* function ( $oldValue, &$ttl, array &$setOpts ) {
*
* @param string $key Cache key
* @param integer $ttl Seconds to live for key updates. Special values are:
- * - WANObjectCache::TTL_NONE : Cache forever
+ * - WANObjectCache::TTL_INDEFINITE: Cache forever
* - WANObjectCache::TTL_UNCACHEABLE: Do not cache at all
* @param callable $callback Value generation function
* @param array $opts Options map:
* since the callback should use slave DBs and they may be lagged or have snapshot
* isolation anyway, this should not typically matter.
* Default: WANObjectCache::TTL_UNCACHEABLE.
- * @param array $oldOpts Unused (mentioned only to avoid PHPDoc warnings)
* @return mixed Value to use for the key
*/
- final public function getWithSetCallback(
- $key, $ttl, $callback, array $opts = array(), $oldOpts = array()
- ) {
- // Back-compat with 1.26: Swap $ttl and $callback
- if ( is_int( $callback ) ) {
- $temp = $ttl;
- $ttl = $callback;
- $callback = $temp;
- }
- // Back-compat with 1.26: $checkKeys as separate parameter
- if ( $oldOpts || ( is_array( $opts ) && isset( $opts[0] ) ) ) {
- $checkKeys = $opts;
- $opts = $oldOpts;
- } else {
- $checkKeys = isset( $opts['checkKeys'] ) ? $opts['checkKeys'] : array();
- }
-
+ final public function getWithSetCallback( $key, $ttl, $callback, array $opts = array() ) {
$pcTTL = isset( $opts['pcTTL'] ) ? $opts['pcTTL'] : self::TTL_UNCACHEABLE;
// Try the process cache if enabled
if ( $value === false ) {
// Fetch the value over the network
- $value = $this->doGetWithSetCallback( $key, $ttl, $callback, $checkKeys, $opts );
+ $value = $this->doGetWithSetCallback( $key, $ttl, $callback, $opts );
// Update the process cache if enabled
if ( $pcTTL >= 0 && $value !== false ) {
$this->procCache->set( $key, $value, $pcTTL );
* @param string $key
* @param integer $ttl
* @param callback $callback
- * @param array $checkKeys
* @param array $opts
* @return mixed
*/
- protected function doGetWithSetCallback(
- $key, $ttl, $callback, array $checkKeys, array $opts
- ) {
+ protected function doGetWithSetCallback( $key, $ttl, $callback, array $opts ) {
$lowTTL = isset( $opts['lowTTL'] ) ? $opts['lowTTL'] : min( self::LOW_TTL, $ttl );
$lockTSE = isset( $opts['lockTSE'] ) ? $opts['lockTSE'] : self::TSE_NONE;
+ $checkKeys = isset( $opts['checkKeys'] ) ? $opts['checkKeys'] : array();
// Get the current key value
$curTTL = null;
return $value;
}
+ /**
+ * @see BagOStuff::makeKey()
+ * @param string ... Key component
+ * @return string
+ * @since 1.27
+ */
+ public function makeKey() {
+ return call_user_func_array( array( $this->cache, __FUNCTION__ ), func_get_args() );
+ }
+
+ /**
+ * @see BagOStuff::makeGlobalKey()
+ * @param string ... Key component
+ * @return string
+ * @since 1.27
+ */
+ public function makeGlobalKey() {
+ return call_user_func_array( array( $this->cache, __FUNCTION__ ), func_get_args() );
+ }
+
/**
* Get the "last error" registered; clearLastError() should be called manually
* @return int ERR_* constant for the "last error" registry
*
* @param mixed $value
* @param integer $ttl [0=forever]
- * @return string
+ * @return array
*/
protected function wrap( $value, $ttl ) {
return array(
$purgeTimestamp = self::parsePurgeValue( $wrapped );
if ( is_float( $purgeTimestamp ) ) {
// Purged values should always have a negative current $ttl
- $curTTL = min( -0.000001, $purgeTimestamp - $now );
+ $curTTL = min( $purgeTimestamp - $now, self::TINY_NEGATIVE );
return array( false, $curTTL );
}
return array( false, null );
}
- if ( $wrapped[self::FLD_TTL] > 0 ) {
+ $flags = isset( $wrapped[self::FLD_FLAGS] ) ? $wrapped[self::FLD_FLAGS] : 0;
+ if ( ( $flags & self::FLG_STALE ) == self::FLG_STALE ) {
+ // Treat as expired, with the cache time as the expiration
+ $age = $now - $wrapped[self::FLD_TIME];
+ $curTTL = min( -$age, self::TINY_NEGATIVE );
+ } elseif ( $wrapped[self::FLD_TTL] > 0 ) {
// Get the approximate time left on the key
$age = $now - $wrapped[self::FLD_TIME];
$curTTL = max( $wrapped[self::FLD_TTL] - $age, 0.0 );
dépôts / lhc / web / wiklou.git / blobdiff