{eac}ObjectCache – a persistent object cache using SQLite & APCu to cache WordPress objects.

Pre-fetch object groups from L2 to L1 cache. Caches and pre-fetches L2 misses (known to not exist in L2 cache).

• Prevents repeated, unnecessary L2 cache reads across requests.

Multisite / Network support:

• Cache/flush/switch by blog id.

Caching statistics:

• Cache hits (typically above 90%).
• Overall and L1/L2 hits, misses, & ratio.
• Cache hits by object groups.
• Number of APCu and SQLite keys stored.
• SQLite select/update/delete/commit counts.

Supports an enhanced superset of WP Object Cache functions. Easily enabled or disabled from {eac}Doojigger administrator page.

• Imports existing MySQL transients.
• Exports cached transients to MySQL when disabled.

Automatically cleans and optimizes SQLite database. Optionally schedule periodic cache invalidation and rebuild. Uses the PHP Data Objects (PDO) extension included with PHP.

While {eac}ObjectCache does support multiple WordPress installations on a single server it does not support multiple servers per installation. SQLite and APCu work only on a single server, not in a clustered or load-balanced environment.

Configuration Alternatives

Assuming you have SQLite and APCu installed, what are your best options?

1. 01Fastest Caching – Uses in-process memory and APCu shared memory. Disable SQLite. * define( 'EAC_OBJECT_CACHE_USE_DB', false );
2. 02Advantage Fast memory-only access.
3. 03Handles concurrent updates through APCu cache.
4. 04Disadvantage APCu may invalidate data under memory constraint.
5. 05APCu cache is not shared with CLI.
6. 06APCu cache is lost on system or PHP restart.
7. 07Less memory (almost as fast) – Uses in-process memory and APCu shared memory. Disable SQLite. * define( 'EAC_OBJECT_CACHE_USE_DB', false );
8. 08Optimize memory use. * define( 'EAC_OBJECT_CACHE_OPTIMIZE_MEMORY', true );
9. 09Advantage Fast memory-only access.
10. 10Handles concurrent updates through APCu cache.
11. 11Conserves per-request memory by not pushing APCu hits to in-process memory.
12. 12Disadvantage Slightly slower to access APCu memory over in-process memory.
13. 13APCu may invalidate data under memory constraint.
14. 14APCu cache is not shared with CLI.
15. 15APCu cache is lost on system or PHP restart.
16. 16Most resilient (and still fast) – Uses in-process memory, APCu shared memory, and SQLite database. Do nothing, this is the default.
17. 17Advantage Most cache hits will come from in-process and APCu memory.
18. 18SQLite retains cache data after restart.
19. 19Disadvantage Must keep SQLite database (on disk) updated.
20. 20Potential concurrency issues on high-volume site.
21. 21Resilient, efficient, and fast (recommended) – Uses in-process memory, APCu shared memory, and SQLite database. Optimize memory use. * define( 'EAC_OBJECT_CACHE_OPTIMIZE_MEMORY', true );
22. 22Advantage Most cache hits will come from in-process and APCu memory.
23. 23Handles concurrent updates better through APCu cache.
24. 24Conserves per-request memory by not pushing APCu hits to in-process memory.
25. 25SQLite retains cache data after restart.
26. 26Disadvantage Slightly slower to access APCu memory over in-process memory.
27. 27Must keep SQLite database (on disk) updated.
28. 28Least efficient (default when APCu is not installed) – Uses in-process memory and SQLite database. Disable APCu. * define( 'EAC_OBJECT_CACHE_USE_APCU', false );
29. 29Advantage Saves resources by not taking up APCu reserves.
30. 30More secure by not using shared memory.
31. 31SQLite retains cache data after restart.
32. 32Disadvantage All cached data initially read from disk.
33. 33Must keep SQLite database (on disk) updated.
34. 34Potential concurrency issues on high-volume site.
35. 35For high-volume sites – reduces or eliminates potential race conditions Optimize memory use. * define( 'EAC_OBJECT_CACHE_OPTIMIZE_MEMORY', true );
36. 36Disable delayed writes. * define( 'EAC_OBJECT_CACHE_DELAYED_WRITES', false );
37. 37Disable use of alloptions array. define( 'EAC_OBJECT_CACHE_DISABLE_ALLOPTIONS', true );
38. 38Advantage Most cache hits will come from in-process and APCu memory.
39. 39Conserves per-request memory by not pushing APCu hits to in-process memory.
40. 40Updates SQLite data immediately.
41. 41Conserves per-request memory by elimination large alloptions array(s).
42. 42Disadvantage Slightly slower to access APCu memory over in-process memory.
43. 43Multiple single-row SQLite update transactions.
44. 44Slightly slower to access individual options from cache rather than alloptions array.

* These options may be set from the {eac}Doojigger administration screen.

When using SQLite, delayed writes (see below) dramatically improves efficiency by only writing updates at the end of the script process.

When using APCu shared memory, data is accessable by other PHP processes that may run on the server.

Inside The Numbers

Label Value

cache hits The total number of requests that returned a cached value.

cache misses The total number of requests that did not return a cached value. This number includes L1 cache (-) , L2 non-persistent , L2 APCu (-) , and L2 SQL misses .

L1 cache hits The number of requests that were found in the L1 memory cache.

L1 cache (+) Request found in the L1 memory cache with data (positive hits).

L1 cache (-) Request found in the L1 memory cache with no data (negative hits).

L1 cache misses The number of requests not found in the L1 memory cache.

L2 non-persistent L1 cache misses in a non-persistent group (not in L2 cache).

L2 APCu hits The number of L1 cache misses (minus L2 non-persistent) that were found in the L2 APCu cache.

L2 APCu (+) Request found in the L2 APCu cache with data (positive hits).

L2 APCu (-) Request found in the L2 APCu cache with no data (negative hits).

L2 APCu misses The number of requests not found in the L2 APCu cache.

L2 SQL hits The number of L2 APCu misses (or L1 cache misses) that were found in the L2 SQLite cache.

L2 SQL misses The number of requests not found in the L2 SQLite cache.

L2 APCu updates The number of APCu keys updated.

L2 APCu deletes The number of APCu keys deleted.

L2 SQL selects The number of SQLite select statements executed.

L2 SQL updates The number of SQLite records updated.

L2 SQL deletes The number of SQLite records deleted.

L2 SQL commits The number of SQLite transactions executed to update and delete records.

• When a request results in a L2 SQL miss , the key is added to the L1 memory or L2 APCu cache as a miss so that additional requests for the same key do not result in additional SQL selects. This is known as a negative hit and still counted as a cache miss making the cache hit ratio (93.10%) understated.

Object cache statistics may be found:

• In the WP Object Cache dashboard panel. Uses $wp_object_cache->showDashboardStats()

In the Debug Bar > Object Cache panel.

• Uses $wp_object_cache->stats()

In the Query Monitor > Logs > Info panel.

• Uses $wp_object_cache->getCurrentStats()

In a wp_admin_notice block when display_stats is set for sampling.

• Uses $wp_object_cache->htmlStats()

Settings

Several cache settings can be modified by adding defined constants to the wp-config.php file. The default settings are recommended and optimal in most cases but individual settings may need to be adjusted based on traffic volume, specific requirements, or unique circumstances. Most of these settings can be adjusted in the {eac}Doojigger administrator screen.

• To disable use of the SQLite Database (default: true): define( 'EAC_OBJECT_CACHE_USE_DB', false );

{eac}ObjectCache will still operate as an in-memory cache without the persistent database. If using APCu memory caching, persistence is maintained as long as the cache is not flushed, manually or by restarting PHP.

• To disable use of the APCu memory cache (default: true if APCu is enabled): define( 'EAC_O