jenkins-bot has submitted this change and it was merged.
Change subject: Make WAN cache HOLDOFF_TTL smaller by combining db/snapshot lag
......................................................................
Make WAN cache HOLDOFF_TTL smaller by combining db/snapshot lag
* In the common ~0 second lag case, transactions up to ~7 seconds
long will have normal set() behavior (instead of just ~5 seconds).
* Like wise with ~0 second transactions tolerating ~7 seconds of
lag (instead of just ~5).
* The lower hold-off time lets caching resume 3 seconds sooner.
Change-Id: I21e2a0a6915492cec422b6a6af5541937745c15b
---
M includes/libs/objectcache/WANObjectCache.php
M tests/phpunit/includes/libs/objectcache/WANObjectCacheTest.php
2 files changed, 49 insertions(+), 16 deletions(-)
Approvals:
Gilles: Looks good to me, approved
jenkins-bot: Verified
diff --git a/includes/libs/objectcache/WANObjectCache.php
b/includes/libs/objectcache/WANObjectCache.php
index 0c7b7ed..d9a8d71 100644
--- a/includes/libs/objectcache/WANObjectCache.php
+++ b/includes/libs/objectcache/WANObjectCache.php
@@ -81,12 +81,10 @@
/** 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
@@ -327,27 +325,34 @@
$lockTSE = isset( $opts['lockTSE'] ) ? $opts['lockTSE'] :
self::TSE_NONE;
$age = isset( $opts['since'] ) ? max( 0, microtime( true ) -
$opts['since'] ) : 0;
$lag = isset( $opts['lag'] ) ? $opts['lag'] : 0;
-
+ // Disallow set() if the source data is uncommitted 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 ( $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;
- $this->logger->warning( "Lowered set() TTL for $key due
to replication lag." );
- }
-
- if ( $age > self::MAX_SNAPSHOT_LAG ) {
+ // Check if there's a risk of writing stale data after the
purge tombstone expired
+ if ( ( $lag + $age ) > self::MAX_READ_LAG ) {
if ( $lockTSE >= 0 ) {
+ // Focus on avoiding stampedes; stash the value
with a low TTL
$tempTTL = max( 1, (int)$lockTSE ); // set()
expects seconds
$this->cache->set( self::STASH_KEY_PREFIX .
$key, $value, $tempTTL );
}
- $this->logger->warning( "Rejected set() for $key due to
snapshot lag." );
+ // Case A: any long-running transaction; ignore this
set()
+ if ( $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
+ return true; // no-op the write for being unsafe
+ // Case B: replication lag is high; 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 C: medium length request during medium 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
+ }
}
$wrapped = $this->wrap( $value, $ttl );
diff --git a/tests/phpunit/includes/libs/objectcache/WANObjectCacheTest.php
b/tests/phpunit/includes/libs/objectcache/WANObjectCacheTest.php
index c3702c5..54393a7 100644
--- a/tests/phpunit/includes/libs/objectcache/WANObjectCacheTest.php
+++ b/tests/phpunit/includes/libs/objectcache/WANObjectCacheTest.php
@@ -313,4 +313,32 @@
$t6 = $this->cache->getCheckKeyTime( $key );
$this->assertEquals( $t5, $t6, 'Check key time did not change'
);
}
+
+ public function testSetWithLag() {
+ $value = 1;
+
+ $key = wfRandomString();
+ $opts = array( 'lag' => 300, 'since' => microtime( true ) );
+ $this->cache->set( $key, $value, 30, $opts );
+ $this->assertEquals( $value, $this->cache->get( $key ),
"Rep-lagged value written." );
+
+ $key = wfRandomString();
+ $opts = array( 'lag' => 0, 'since' => microtime( true ) - 300 );
+ $this->cache->set( $key, $value, 30, $opts );
+ $this->assertEquals( false, $this->cache->get( $key ),
"Trx-lagged value not written." );
+
+ $key = wfRandomString();
+ $opts = array( 'lag' => 5, 'since' => microtime( true ) - 5 );
+ $this->cache->set( $key, $value, 30, $opts );
+ $this->assertEquals( false, $this->cache->get( $key ), "Lagged
value not written." );
+ }
+
+ public function testWritePending() {
+ $value = 1;
+
+ $key = wfRandomString();
+ $opts = array( 'pending' => true );
+ $this->cache->set( $key, $value, 30, $opts );
+ $this->assertEquals( false, $this->cache->get( $key ), "Pending
value not written." );
+ }
}
--
To view, visit https://gerrit.wikimedia.org/r/248734
To unsubscribe, visit https://gerrit.wikimedia.org/r/settings
Gerrit-MessageType: merged
Gerrit-Change-Id: I21e2a0a6915492cec422b6a6af5541937745c15b
Gerrit-PatchSet: 2
Gerrit-Project: mediawiki/core
Gerrit-Branch: master
Gerrit-Owner: Aaron Schulz <asch...@wikimedia.org>
Gerrit-Reviewer: Gilles <gdu...@wikimedia.org>
Gerrit-Reviewer: jenkins-bot <>
_______________________________________________
MediaWiki-commits mailing list
MediaWiki-commits@lists.wikimedia.org
https://lists.wikimedia.org/mailman/listinfo/mediawiki-commits
