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Improve MultiWriteBagOStuff::merge() cross-DC performance

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Implement merge() by getting a lock on the tier 1
cache, getting it's value, generating the new one,
writing to all tiers, and then unlocking tier 1.
This is done by just using the stock mergeViaLock().

This means that if tier 1 is in the same DC, the
other tiers only need 1 request each, just for set().

Change-Id: I4b0c303ef3b86b63e7630032ed0b010e79706324
This commit is contained in:
Aaron Schulz 2015-10-20 21:50:27 -07:00
parent 445136b5bf
commit 6463cd02f7
1 changed files with 7 additions and 11 deletions
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18
includes/objectcache/MultiWriteBagOStuff.php
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@ -106,6 +106,13 @@ class MultiWriteBagOStuff extends BagOStuff {
}
protected function doGet( $key, $flags = 0 ) {
if ( ( $flags & self::READ_LATEST ) == self::READ_LATEST ) {
// If the latest write was a delete(), we do NOT want to fallback
// to the other tiers and possibly see the old value. Also, this
// is used by mergeViaLock(), which only needs to hit the primary.
return $this->caches[0]->get( $key, $flags );
}
$misses = 0; // number backends checked
$value = false;
foreach ( $this->caches as $cache ) {
@ -192,17 +199,6 @@ class MultiWriteBagOStuff extends BagOStuff {
return $this->caches[0]->unlock( $key );
}
/**
* @param string $key
* @param callable $callback Callback method to be executed
* @param int $exptime Either an interval in seconds or a unix timestamp for expiry
* @param int $attempts The amount of times to attempt a merge in case of failure
* @return bool Success
*/
public function merge( $key, $callback, $exptime = 0, $attempts = 10 ) {
return $this->doWrite( self::ALL, 'merge', $key, $callback, $exptime );
}
public function getLastError() {
return $this->caches[0]->getLastError();
}