Title: Yac Object Cache
Author: laruence
Published: 02 September 2026
Last modified: 10 September 2026
---
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# Yac Object Cache
De [laruence](https://profiles.wordpress.org/laruence/)
[Download](https://downloads.wordpress.org/plugin/yac-object-cache.1.3.0.zip)
* [Details](https://lij.wordpress.org/plugins/yac-object-cache/#description)
* [Reviews](https://lij.wordpress.org/plugins/yac-object-cache/#reviews)
* [Installation](https://lij.wordpress.org/plugins/yac-object-cache/#installation)
* [Development](https://lij.wordpress.org/plugins/yac-object-cache/#developers)
[Supòrto](https://wordpress.org/support/plugin/yac-object-cache/)
## Description
[Yac](https://github.com/laruence/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.⌉⌊Dashboard widget: hit rate, uptime, key slots, values occupied and the
24-hour counters.⌉[
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.⌉⌊
Tools → Yac Object Cache: the status bar, with the live shared-memory round trip
.⌉[
Tools Yac Object Cache: the status bar, with the live shared-memory round trip.
[⌊Tools → Yac Object Cache: cache status — hit rate, hits and misses over Today /
Yesterday / Last 7 days, with the capacity diagnosis on hover.⌉⌊Tools → Yac Object
Cache: cache status — hit rate, hits and misses over Today / Yesterday / Last 7
days, with the capacity diagnosis on hover.⌉[
Tools Yac Object Cache: cache status — hit rate, hits and misses over Today / Yesterday/
Last 7 days, with the capacity diagnosis on hover.
[⌊Tools → Yac Object Cache: shared memory contents — keys-by-group pie, occupancy
totals and the largest (or hottest) entries, each clickable for the entry inspector.⌉⌊
Tools → Yac Object Cache: shared memory contents — keys-by-group pie, occupancy
totals and the largest (or hottest) entries, each clickable for the entry inspector
.⌉[
Tools Yac Object Cache: shared memory contents — keys-by-group pie, occupancy totals
and the largest (or hottest) entries, each clickable for the entry inspector.
## Installation
1. Install the Yac extension, any of three ways (then enable `extension=yac.so` in
php.ini):
2. PECL
3. pecl install yac
4. PIE (the PHP Foundation’s PECL successor; yac is on Packagist)
5. pie install laruence/yac
Or from source: download the latest [release](https://github.com/laruence/yac/releases),
unzip it, then inside:
```
phpize && ./configure && make && make install
```
1. 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-e
### 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 `::` (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.
Contributors
* [ laruence ](https://profiles.wordpress.org/laruence/)
[Translate “Yac Object Cache” into your language.](https://translate.wordpress.org/projects/wp-plugins/yac-object-cache)
### Interested in development?
[Browse the code](https://plugins.trac.wordpress.org/browser/yac-object-cache/),
check out the [SVN repository](https://plugins.svn.wordpress.org/yac-object-cache/),
or subscribe to the [development log](https://plugins.trac.wordpress.org/log/yac-object-cache/)
by [RSS](https://plugins.trac.wordpress.org/log/yac-object-cache/?limit=100&mode=stop_on_copy&format=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: `::` 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.
## Mêta
* Version **1.3.0**
* Last updated **9 hours ago**
* Active installations **Fewer than 10**
* WordPress version ** 5.6 or higher **
* Tested up to **7.1**
* PHP version ** 7.0 or higher **
* Language
* [English (US)](https://wordpress.org/plugins/yac-object-cache/)
* Tags
* [cache](https://lij.wordpress.org/plugins/tags/cache/)[object cache](https://lij.wordpress.org/plugins/tags/object-cache/)
[performance](https://lij.wordpress.org/plugins/tags/performance/)
* [Advanced View](https://lij.wordpress.org/plugins/yac-object-cache/advanced/)
## Ratings
No reviews have been submitted yet.
[Your review](https://wordpress.org/support/plugin/yac-object-cache/reviews/#new-post)
[See all reviews](https://wordpress.org/support/plugin/yac-object-cache/reviews/)
## Contributors
* [ laruence ](https://profiles.wordpress.org/laruence/)
## Supòrto
Got something to say? Need help?
[View support forum](https://wordpress.org/support/plugin/yac-object-cache/)