Descripción

Yac uses the Yac PHP extension as the backing store for the WordPress object cache.

Unlike Memcached or Redis, Yac stores data in shared memory inherited by every PHP-FPM worker on the machine. There is no cache server to install, no socket to configure, and every cache read is a hash lookup in local memory — typically microseconds, with no network round trip and no global lock.

Highlights

Fast. A cache read is a shared-memory hash lookup — the status page measures a 0.005 ms round trip. On a production site (laruence.com, PHP 8.1-FPM, 8 cores), full homepage renders ran ~20% faster than the classic Memcached drop-in: 141.6 vs 118.7 req/s at 20 concurrent users, +18-20% across 20-100 concurrency, zero failed requests.
No external server. The cache lives in shared memory (mmap/SysV), fork-inherited by FPM workers.
Lock-free. Per-slot CAS arbitration; throughput scales with worker count. No global lock.
Self-deploying. Activating the plugin writes object-cache.php to wp-content/.
Simple keys, simple flush. Keys are stored verbatim while they fit Yac’s 48-byte limit; wp_cache_flush() calls Yac::flush() and wipes the entire shared memory on the machine — know that before you flush.
Graceful degradation. If Yac is unavailable (extension missing), the drop-in falls back to a per-request in-memory cache and WordPress keeps working.
Single-node focus. Keys carry no per-blog prefix; installs sharing one PHP pool isolate via YAC_OCACHE_KEY_PREFIX. Multisite blogs share one namespace.
Entry inspector. On the admin page, click any top-entry key to see the deserialized value, padded size, expiry and — on newer yac builds — last access, hit count and whether the value is embedded in its slot; or delete the entry.

Best fit

Yac is a local cache. It is ideal for single-node or few-node WordPress installs where all PHP workers run on one machine. On large multi-server clusters with strict cross-node consistency needs, a network cache (Memcached/Redis) may suit better.

Capturas

Cache health dashboard: hit-rate ring, cause-attributed metric bars and the live shared-memory round trip (0.005 ms).

Storage overview: key slots in use, lookups, hit rate, values-memory pool and the memory-health verdict. — Cache health dashboard: hit-rate ring, cause-attributed metric bars and the live shared-memory round trip (0.005 ms).

Instalación

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
Build from source
git clone https://github.com/laruence/yac.git && cd yac phpize && ./configure && make && sudo make install
Install and activate Yac Object Cache. Activation deploys wp-content/object-cache.php.
In wp-config.php, above the "That’s all, stop editing!" line, add:

define( 'WP_CACHE', true ); define( 'YAC_OCACHE_KEY_PREFIX', 'ab_' ); // unique per install when sites share one PHP pool

That is it. Visit Tools Yac Object Cache to verify status.

Optional php.ini tuning

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

Optional wp-config switches

define( 'YAC_OCACHE_EMPTY_TTL', 0 );    // default 21600: lifetime cap (seconds) on empty-array negative cache results; set 0 to disable
define( 'YAC_OCACHE_DISABLE', true );     // emergency 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 in-memory cache. Your site keeps working; you just lose cross-request persistence. The status page flags the missing extension.
How are keys stored, given Yac’s 48-byte key limit?: Storage keys are <YAC_OCACHE_KEY_PREFIX>:<group>:<key> (default prefix wp), kept verbatim while they fit the 48-byte budget; over-long keys keep the group verbatim and hash (crc32b) only the key part. Keys carry no per-blog prefix: use a different YAC_OCACHE_KEY_PREFIX per install when sites share one PHP pool; multisite blogs share the namespace.
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 before flushing.
Multisite?: Yes, with a caveat: blogs of one install share the cache namespace (keys carry no blog prefix), which is fine for most sites; switch_to_blog() does not re-namespace keys. Run separate installs with different YAC_OCACHE_KEY_PREFIX values when blogs must not share 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 WordPress core does not rely on it.

Reseñas

No hay reseñas para este plugin.

Colaboradores y desarrolladores

"Yac Object Cache" es un software de código abierto. Las siguientes personas han colaborado con este plugin.

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Registro de cambios

1.2.2

Fixed stale shared-memory writes: within one request, wp_cache_set() on a key already written by wp_cache_add() in that same request skipped the shared-memory write, so other requests kept reading the value the add stored (the update_option() pattern — add() inside get_option(), then set() — left the old option behind).
Replaced YAC_OCACHE_SKIP_EMPTY with YAC_OCACHE_EMPTY_TTL (default 21600s): empty results (bot-probed get_page_by_path() paths, comment query misses) now share as usual but expire after that lifetime instead of occupying a slot forever. Set 0 to disable the cap.
The health panel’s "keys used" now reports the number of live entries rather than the slots_used high-water mark.

1.2.1

Placed the PHPCS EscapeOutput annotations around the health-ring output so WordPress.org Plugin Check recognizes the exemption (the previous inline annotation sat on the wrong line of the multi-line statement).
Annotated pre_wp_cache_get in the drop-in as a WordPress core hook.

1.2.0

Fixed the health-ring donut on the admin dashboard disappearing: the SVG was piped through wp_kses_post(), whose allowed-tag list strips SVG elements and left only the center text visible.
Renamed every plugin-owned symbol from the wp_yac_/WP_YAC_/wp-yac- prefixes to yac_ocache_/YAC_OCACHE_/yac-ocache- for WordPress.org prefix policy (the wp_ prefix is reserved for WordPress core). The wp-config switches were renamed accordingly: YAC_OCACHE_KEY_PREFIX, YAC_OCACHE_SKIP_EMPTY, YAC_OCACHE_DISABLE, YAC_OCACHE_WARMUP_LOOKUPS.
The wp_cache_* functions and the $wp_object_cache global are the standard WordPress object cache API and keep their names.
WP-CLI: the commands stay wp yac status / wp yac flush; the command class is now YAC_OCACHE_CLI_Command.

1.1.1

A stored false is now written to shared memory as 0. Yac’s get() returns false for both a miss and a stored false, so false negatives never survived past the request; with 0 they persist like any other value (readers comparing by value see 0 instead of false).
Admin page: top entries grew a Hottest tab (by access count) alongside Largest, shown whenever this yac build reports per-entry hits; the entry inspector gains Hits, Embedded-in-slot and compressed-payload (c_len) metadata.
Admin page: entry listings now page through Yac::dump() 1000 entries at a time instead of one dump(-1), which could exhaust the PHP memory limit on a busy cache; builds older than 2.4.0 fall back to the single full dump.

1.1.0

Dashboard rebuilt around a cache-health verdict: hit-rate ring, cause-attributed metric bars, keys-by-group pie, largest entries by content length, configuration reference and runtime diagnostics.
Key format rework: <prefix>:<group>:<key> with no per-blog prefix (default prefix wp); over-long keys keep the group verbatim and hash only the key part; switch_to_blog() no longer re-namespaces keys.
YAC_OCACHE_SKIP_EMPTY (on by default): empty get_page_by_path: negatives (bot 404 probes) stay request-local instead of filling slots.
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, and graceful runtime-only fallback.
Storage key prefix configurable via YAC_OCACHE_KEY_PREFIX (0-6 chars, default wp_); shorter is better.
wp_cache_flush() calls Yac::flush() and clears the entire shared memory on the machine — the admin page asks for confirmation and states the scope.
Admin dashboard: status bar, key-slot donut, counters, memory-health advice, diagnostics, self-test, memory-contents snapshot, and the configuration reference inside the Environment panel.

Descripción

Capturas

Instalación

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()?