Aaron Schulz has uploaded a new change for review.
https://gerrit.wikimedia.org/r/118800
Change subject: Tweaked "latest" handling of filebackend stat entries
......................................................................
Tweaked "latest" handling of filebackend stat entries
* Track the stat cache time and compute "latest" dynamically.
Storing "latest" was too strict and also did not work well
since "latest" entries did not override non-"latest" ones
due to the use of add(). This should avoid some cache misses.
Change-Id: I1e9391039537d608b89773b4d51575e3b364a751
---
M includes/filebackend/FileBackendStore.php
1 file changed, 18 insertions(+), 2 deletions(-)
git pull ssh://gerrit.wikimedia.org:29418/mediawiki/core
refs/changes/00/118800/1
diff --git a/includes/filebackend/FileBackendStore.php
b/includes/filebackend/FileBackendStore.php
index 16300af..67f8b8c 100644
--- a/includes/filebackend/FileBackendStore.php
+++ b/includes/filebackend/FileBackendStore.php
@@ -50,6 +50,7 @@
protected $mimeCallback;
protected $maxFileSize = 4294967296; // integer bytes (4GiB)
+ protected $consistencyWindow = 30; // integer; seconds of eventual
consistency
const CACHE_TTL = 10; // integer; TTL in seconds for process cache
entries
const CACHE_CHEAP_SIZE = 500; // integer; max entries in "cheap cache"
@@ -1650,9 +1651,15 @@
}
/**
- * Set the cached stat info for a file path.
+ * Set the cached stat info for a file path
+ *
* Negatives (404s) are not cached. By not caching negatives, we can
skip cache
* salting for the case when a file is created at a path were there was
none before.
+ *
+ * The cache duration is factor of how long it has been since the file
last changed.
+ * The cache time is also tracked in the stat info. Unless the file
changes, the cache
+ * TTL increases each miss and the gap between last change and cache
time increases.
+ * The chance of staleness due to eventual consistency goes down over
time.
*
* @param string $path Storage path
* @param array $val Stat information to cache
@@ -1662,7 +1669,10 @@
if ( $path === null ) {
return; // invalid storage path
}
- $age = time() - wfTimestamp( TS_UNIX, $val['mtime'] );
+ unset( $val['latest'] ); // only useful for process cache
+ $now = time();
+ $val['asof'] = wfTimestamp( TS_MW, $now );
+ $age = $now - wfTimestamp( TS_UNIX, $val['mtime'] );
$ttl = min( 7 * 86400, max( 300, floor( .1 * $age ) ) );
$this->memCache->add( $this->fileCacheKey( $path ), $val, $ttl
);
}
@@ -1716,6 +1726,12 @@
$values = $this->memCache->getMulti( array_keys( $pathNames ) );
foreach ( $values as $cacheKey => $val ) {
if ( is_array( $val ) ) {
+ // Find out how long the cache time is after
the reported mtime
+ $delay = isset( $val['asof'] )
+ ? wfTimestamp( TS_UNIX, $val['asof'] )
- wfTimestamp( TS_UNIX, $val['mtime'] )
+ : INF;
+ // If the cache time was safely after the
mtime, flag it as "latest info"
+ $val['latest'] = ( $delay >
$this->consistencyWindow );
$path = $pathNames[$cacheKey];
$this->cheapCache->set( $path, 'stat', $val );
if ( isset( $val['sha1'] ) ) { // some backends
store SHA-1 as metadata
--
To view, visit https://gerrit.wikimedia.org/r/118800
To unsubscribe, visit https://gerrit.wikimedia.org/r/settings
Gerrit-MessageType: newchange
Gerrit-Change-Id: I1e9391039537d608b89773b4d51575e3b364a751
Gerrit-PatchSet: 1
Gerrit-Project: mediawiki/core
Gerrit-Branch: master
Gerrit-Owner: Aaron Schulz <[email protected]>
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