Description

Yac keeps the cache in shared memory inherited by every PHP-FPM worker on the machine, so a read is a hash lookup in local memory — no cache server, no socket, no network.

Highlights

Fast. No socket, no network, no global lock — per-slot CAS, so throughput scales with workers. A 0.005 ms round trip, and ~19% faster page renders than the Memcached drop-in (141.6 vs 118.7 req/s).
Nothing to operate. No cache server to install, secure, monitor or restart.
Health you can read. Hit rate, hits and misses charted over Today / Yesterday / Last 7 days, with a diagnosis that also says when not to add memory.
Fails soft. No extension, or yac.enable=0, degrades to a per-request cache and the site keeps serving.

Best fit

Single-node or few-node installs where all PHP workers share a machine. For multi-server clusters needing cross-node consistency, a network cache (Memcached/Redis) suits better.

Screenshots

Dashboard widget: hit rate, uptime, key slots, values occupied and the 24-hour counters.

Tools → Yac Object Cache: the status bar, with the live shared-memory round trip. — Dashboard widget: hit rate, uptime, key slots, values occupied and the 24-hour counters.

Installation

Install the Yac extension, any of three ways (then enable extension=yac.so in php.ini):
PECL
pecl install yac
PIE (the PHP Foundation’s PECL successor; yac is on Packagist)
pie install laruence/yac

Or from source: download the latest release, unzip it, then inside:

phpize && ./configure && make && make install

Install and activate Yac Object Cache. Activation deploys wp-content/object-cache.php.

That is it — no wp-config edit needed. Visit Tools Yac Object Cache to verify status.

Optional php.ini tuning

yac.enable = 1
yac.keys_memory_size = 16M      ; ~128K slots (~32K per 4M)
yac.values_memory_size = 64M    ; raise for large sites (big alloptions)

Optional wp-config switches

define( 'YAC_OCACHE_KEY_PREFIX', 'ab' ); // default wp; give each install its own when sites share one PHP pool
define( 'YAC_OCACHE_EMPTY_TTL', 0 );     // default 21600s: lifetime cap on empty negative results; 0 disables
define( 'YAC_OCACHE_DISABLE', true );    // escape hatch: force runtime-only mode

FAQ

Do I need a Memcached or Redis server?: No. That is the point — the cache lives in shared memory on the machine.
What happens if the Yac extension is not installed?: The drop-in degrades to a per-request cache: the site keeps working, you lose cross-request persistence, and the status page flags the missing extension.
How are keys stored, given Yac’s 48-byte key limit?: As <YAC_OCACHE_KEY_PREFIX>:<group>:<key> (default prefix wp), verbatim while they fit the 48-byte budget; over-long keys keep the group verbatim and hash (crc32b) only the key part.
Does flush() clear other Yac users on the same machine?: Yes. wp_cache_flush() calls Yac::flush(), which wipes the entire shared memory on the machine, including data written by other Yac users sharing the PHP pool. The admin page asks for confirmation first.
Multisite?: Yes, with a caveat: keys carry no per-blog prefix, so blogs of one install share the namespace and switch_to_blog() does not re-namespace. Give each install its own YAC_OCACHE_KEY_PREFIX when sites sharing a PHP pool must not see each other’s entries.
What about wp_cache_flush_group()?: Yac cannot delete entries by prefix, so a group flush clears the request-level copy of that group; shared entries then expire via TTL. The plugin reports flush_group as unsupported so core does not rely on it.

Reviews

There are no reviews for this plugin.

Contributors & Developers

“Yac Object Cache” is open source software. The following people have contributed to this plugin.

laruence

Translate “Yac Object Cache” into your language.

Interested in development?

Browse the code, check out the SVN repository, or subscribe to the development log by RSS.

Changelog

1.3.0

No wp-config edit is needed any more: WP_CACHE is no longer required or reported. WordPress loads object-cache.php regardless of it — that constant only gates advanced-cache.php (page caching), which this plugin does not provide. The live CI run now boots WordPress without it to prove the point.
The Cache health panel became a client-side trend chart: hit rate, hits and misses over Today / Yesterday / Last 7 days, with the window’s counters and the capacity diagnosis on hover. Counters are sampled every 15 minutes into a ~7-day ring.
Fixed the entry inspector exhausting the PHP memory limit on a busy cache: it now pages through Yac::dump() instead of accumulating the whole dump.
Fixed the dashboard widget reporting “0 bytes” for values occupied. The Active bar now also shows shared-memory uptime.
Suggested tuning raised to yac.keys_memory_size = 16M (~128K slots); 4M gives only ~32K.

1.2.2

Fixed stale shared-memory writes: wp_cache_set() on a key already written by wp_cache_add() in the same request skipped the shared write, so other requests kept reading the value the add stored (the update_option() pattern left the old option behind).
Replaced YAC_OCACHE_SKIP_EMPTY with YAC_OCACHE_EMPTY_TTL (default 21600s): empty results now share as usual but expire instead of occupying a slot forever.
The health panel’s “keys used” reports live entries rather than the slots_used high-water mark.

1.2.1

Moved the PHPCS EscapeOutput annotations so WordPress.org Plugin Check recognizes the exemption; annotated pre_wp_cache_get as a core hook.

1.2.0

Fixed the health-ring donut disappearing: wp_kses_post() strips SVG elements.
Renamed every plugin-owned symbol to the yac_ocache_/YAC_OCACHE_/yac-ocache- prefixes for WordPress.org policy (wp_ is reserved for core). The wp_cache_* functions and $wp_object_cache keep their standard names; WP-CLI stays wp yac status / wp yac flush.

1.1.1

A stored false is now written as 0: Yac’s get() returns false for both a miss and a stored false, so a stored false never survived past the request.
Top entries grew a Hottest tab (by access count) alongside Largest; the entry inspector gained Hits, Embedded-in-slot and c_len.
Entry listings page through Yac::dump() instead of one dump(-1), which could exhaust the memory limit.

1.1.0

Dashboard rebuilt around a cache-health verdict, keys-by-group pie, largest entries, configuration reference and diagnostics.
Key format rework: <prefix>:<group>:<key> with no per-blog prefix; over-long keys hash only the key part.
YAC_OCACHE_DISABLE escape hatch forces runtime-only mode.

1.0.0

Initial release. Yac-backed object cache with self-deploying drop-in, verbatim keys with hashed fallback, multisite support, graceful runtime-only fallback, and the admin dashboard.

Description

Screenshots

Installation

FAQ

Do I need a Memcached or Redis server?

What happens if the Yac extension is not installed?

How are keys stored, given Yac’s 48-byte key limit?

Does flush() clear other Yac users on the same machine?

Multisite?

What about wp_cache_flush_group()?