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

The {eac}ObjectCache is a light-weight and very efficient drop-in persistent object cache that uses a fast SQLite database and even faster APCu shared memory to cache WordPress objects. See The WordPress Object Cache

The WordPress Object Cache is used to save on trips to the database. The Object Cache stores all of the cache data to memory and makes the cache contents available by using a key, which is used to name and later retrieve the cache contents. By default, the object cache is non-persistent. This means that data stored in the cache resides in memory only and only for the duration of the request. Cached data will not be stored persistently across page loads unless you install a persistent caching plugin.

Here, an object is any piece of data - a number, text, a set of database records, an API response, etc. - that can be referenced by a name or key. Objects are categorized by a group name. Groups help identify what an object is and how it is used. {eac}ObjectCache replaces the default WordPress object cache to not only store data in process memory but to also store data persistently, across requests, in APCu shared memory and/or in a SQLite database, increasing the likelihood of cache hits and decreasing the need for costly computations, complex MySQL database queries, and remote API requests. SQLite is a fast, small, single-file relational database engine. By using SQLite to store objects, {eac}ObjectCache is able to manage a relatively large amount of data (groups, keys, and values) in a very efficient and fast data-store. APCu is a shared, in-memory, persistent cache available only when the APCu PECL Extension is installed. {eac}ObjectCache uses APCu as an intermediate cache between the L1 memory cache and the L2 SQLite database cache providing extremely fast object retrieval, {eac}ObjectCache always uses per-request, in-memory caching and may operate with either APCu memory caching or SQLite database caching - or both. APCu memory caching uses a single block of memory shared by all PHP requests and is persistent until and unless the cache is cleared or the server is rebooted (or PHP restarted). SQLite database caching is persistent until and unless the cache is deliberately cleared. Features

• Lightweight, efficient, and fast!
• L1 (in-process memory) and L2 (APCu & SQLite) caching.
• Supports Write-Back (delayed transactions) or Write-Through SQL caching.
• Caching by object group name.
• Preserves uniqueness of keys.
• Manage keys by group name.
• Supports group name attributes (:sitewide, :nocaching, :permanent, :prefetch)
• 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/APCu/L2 hits, misses, & ratio.
• L1 hits by object groups.
• Number of APCu and SQLite keys stored.
• L2 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 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. Fastest Caching
2. Disable SQLite. [^1]
3. define( 'EAC_OBJECT_CACHE_USE_DB', false );
4. Uses in-process memory and APCu shared memory.
5. Advantage
6. Fast memory-only access.
7. Disadvantage
8. APCu may invalidate data under memory constraint.
9. APCu cache is lost on system or PHP restart.
10. Less memory (almost as fast)
11. Disable SQLite. [^1]
12. define( 'EAC_OBJECT_CACHE_USE_DB', false );
13. Optimize memory use. [^1]
14. define( 'EAC_OBJECT_CACHE_OPTIMIZE_MEMORY', true );
15. Uses in-process memory and APCu shared memory.
16. Advantage
17. Fast memory-only access.
18. Conserves per-request memory by not pushing APCu hits to in-process memory.
19. Disadvantage
20. Slightly slower to access APCu memory over in-process memory.
21. APCu may invalidate data under memory constraint.
22. APCu cache is lost on system or PHP restart.
23. Most resilient (and still fast)
24. Do nothing, this is the default.
25. Uses in-process memory, APCu shared memory, and SQLite database.
26. Advantage
27. Most cache hits will come from in-process and APCu memory.
28. SQLite retains cache data after restart.
29. Disadvantage
30. Must keep SQLite database (on disk) updated.
31. Resilient, efficient, and fast (recommended)
32. Optimize memory use. [^1]
33. define( 'EAC_OBJECT_CACHE_OPTIMIZE_MEMORY', true );
34. Uses in-process memory, APCu shared memory, and SQLite database.
35. Advantage
36. Most cache hits will come from in-process and APCu memory.
37. Conserves per-request memory by not pushing APCu hits to in-process memory.
38. SQLite retains cache data after restart.
39. Disadvantage
40. Slightly slower to access APCu memory over in-process memory.
41. Must keep SQLite database (on disk) updated.
42. Least efficient (default when APCu is not installed)
43. Disable APCu. [^1]
44. define( 'EAC_OBJECT_CACHE_USE_APCU', false );
45. Uses in-process memory and SQLite database.
46. Advantage
47. Saves resources by not taking up APCu reserves.
48. SQLite retains cache data after restart.
49. Disadvantage
50. All cached data read from disk.
51. Must keep SQLite database (on disk) updated.

[^1]: 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. 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.

{eac}ObjectCache is an extension plugin to and is fully functional with installation and registration of {eac}Doojigger. However, the core object-cache.php file may be installed without {eac}Doojigger (referred to as 'detached' mode). In detached mode, the plugin will attempt to copy the object-cache.php file to the /wp-content folder on activation, or you may manually copy the object-cache.php file from the plugin /src folder to the /wp-content folder to activate. Options can then be set using the documented PHP constants in the wp-config.php file. Automatic Plugin Installation This plugin is available from the WordPress Plugin Repository and can be installed from the WordPress Dashboard » Plugins » Add New page. Search for 'EarthAsylum', click the plugin's [Install] button and, once installed, click [Activate]. See Managing Plugins -> Automatic Plugin Installation Upload via WordPress Dashboard Installation of this plugin can be managed from the WordPress Dashboard » Plugins » Add New page. Click the [Upload Plugin] button, then select the eacobjectcache.zip file from your computer. See Managing Plugins -> Upload via WordPress Admin Manual Plugin Installation You can install the plugin manually by extracting the eacobjectcache.zip file and uploading the 'eacobjectcache' folder to the 'wp-content/plugins' folder on your WordPress server. See Managing Plugins -> Manual Plugin Installation Settings Once installed and activated, options for this extension will show in the 'Object Cache' tab of {eac}Doojigger settings.

Additional Information {eac}ObjectCache is an extension plugin to and is fully functional with installation and registration of {eac}Doojigger. However, the core object-cache.php file may be installed without {eac}Doojigger - referred to as 'detached' mode. In detached mode, the plugin will attempt to copy the object-cache.php file to the /wp-content folder on activation, or you may manually copy the object-cache.php file from the plugin /src folder to the /wp-content folder to activate. Options can then be set using the documented PHP constants in the wp-config.php file. See Also {eac}KeyValue - An easy to use, efficient, key-value pair storage mechanism for WordPress that takes advatage of the WP Object Cache.

Version 2.0.0 – September 30, 2025

• Added support for APCu caching as an intermediate layer between L1 and L2 caching.
• Add EAC_OBJECT_CACHE_USE_DB constant to disable DB use.
• Add EAC_OBJECT_CACHE_USE_APCU constant to disable APCu use.
• Add EAC_OBJECT_CACHE_OPTIMIZE_MEMORY constant when using APCu.
• Removed bulk import of transients on install/rebuild.
• Added single import of transient on demand.
• Use default flush_group() for wp_cache_set_last_changed hook.
• Removed select_all(), use select_each().
• Add log_stats flag and check for external logging plugins.
• Verify Query Manager active before triggering actions.
• Type hint class variables.
• Updated administrator page.
• Rework stats arrays - 0=>hits, 1=>count, 2=>size (db total adds 3=>file size).
• Many other internal changes and optimizations.

Version 1.4.1 – July 12, 2025

• Implemented cache_clear_query_groups() on wp_cache_set_last_changed hook to invalidate group cache for query groups.
• See https://make.wordpress.org/core/2023/07/17/improvements-to-the-cache-api-in-wordpress-6-3/
• New wp_cache_add_group_expire( $groups ) to set default ttl by group.
• New EAC_OBJECT_CACHE_GROUP_EXPIRE to set default ttl by group.
• Use instanceof instead of is_a() when checking WP_Object_Cache.

Version 1.4.0 – June 27, 2025

• Issue: Although setting wp_using_ext_object_cache( false ) would seem to disable use of the object cache, this setting is rarely used.
• Fix: (A) check wp_using_ext_object_cache() on each external function call (i.e. wp_cache_get()). This has NOT been implemented as it is likely to cause many issues throughout WordPress by disabling all object caching.
• Fix: (B) selectively check wp_using_ext_object_cache() within the object-cache code. This has been implemented to suppress L2 (database) access only, retaining access to the current L1 (memory) cache.
• wp_using_ext_object_cache( false ) may temporarily disable L2 caching while allowing L1 access.
• New (internal) select_cursor(), select_each(), and updated select_all() methods for better cursor/array management when retrieving multiple records from L2.
• New (non-standard) sub-group or group name suffix to indicate specific attributes of a group:
• Global group - {group}:sitewide (applies to all sites in a multi-site network).
• Non-Persistent group - {group}:nocaching (not saved in the L2 cache).
• Permanent group - {group}:permanent (no expiration time required or set).
• Prefetch group - {group}:prefetch (load to L1 cache on startup).
• Enforce wp_suspend_cache_addition() on wp_cache_set() if the key doesn't already exist.
• Circumvent $wpdb->query by using $wpdb->dbh with MySQLi to retrieve individual rows when importing transients.
• Use SQL (not get_option) to get expiration when importing transients.
• Set wp_suspend_cache_addition(true) and wp_using_ext_object_cache(true) when exporting transients to MySQL.
• Don't set wp_installing(true) when importing transients.
• New EAC_OBJECT_CACHE_DISABLE_TRANSIENT_IMPORT / EXPORT constants.
• Fixed potential critical error on cache create caused by file permissions.

Version 1.3.4 – June 17, 2025

• Fixed bug (potential crash) introduced with persisting prefetch groups.

Version 1.3.3 – June 10, 2025

• Save (persist) added prefetch groups since pre-fetching happens before add.
• Don't check database for prefetch group keys after pre-fetching.

Version 1.3.2 – June 3, 2025

• Fix error in object-cache.php & ObjectCache.admin when FS_CHMOD_FILE/DIR is not defined.

Version 1.3.1 – April 19, 2025

• Compatible with WordPress 6.8.
• Prevent _load_textdomain_just_in_time was called incorrectly notice from WordPress.
• All extensions - via eacDoojigger 3.1.
• Modified extension registration in constructor.

Version 1.3.0 - April 11, 2025

• Support for 'detached' mode (installed without {eac}Doojigger)...
• Installs/uninstalls object-cache.php on activation/deactivation hooks.
• Or manually install src/object-cache.php to the wp-content folder.
• Added option to purge/rebuild cache on a scheduled (hourly, twicedaily, daily, weekly, monthly) basis.
• Manually: add_action( 'some_weekly_event', [ $wp_object_cache, 'rebuild_object_cache' ] );
• assuming some_weekly_event has been scheduled with wp_schedule_event(...).
• Added get_group(), returns all L1 & L2 keys for a group.
• Added delete_group() deletes all L1 & L2 keys for a group.
• flush_group() is immediate, delete_group() fetches rows and caches deletes.
• Added set_transient_doing_cron to write_hooks array.
• Forces cache write when setting doing_cron transient.
• Removed action_scheduler_before_process_queue action that prevented runtime cache flush.

Version 1.2.2 - April 4, 2025

• New write_hooks sets hook names that trigger an immediate cache write.
• Default is [ 'cron_request', 'updated_option_cron' ] to fix wp-cron jobs not running or rescheduling correctly.
• Can be set/overridden with EAC_OBJECT_CACHE_WRITE_HOOKS constant.
• Added action on action_scheduler_before_process_queue hook to prevent cache flush triggered by Action Scheduler.

Version 1.2.1 - March 30, 2025

• Use add_event_task filter to add optimize scheduled task.
• Fix probability error when set to 25.

Version 1.2.0 - March 20, 2025

• Optimize insert... on conflict statement.
• Use exec() instead of query() where applicable.
• Optimize stats sample select SQL.
• Rework count/size in cache stats.
• Don't wait for mu_plugins to load prefetch groups.
• Added optimize() method with scheduled event (daily @1am).
• Purge expired records before vacuum.
• Added incremental_vacuum on maintenance probability.
• Allow defined constants to prevent outside actors from flushing caches.
• Reworked option constants load.
• Support Query Monitor logging and timings.
• Prevent maintenance on ajax/cron/not-php requests.
• New init() to allow instantiation before triggering use.
• New getStatsCache(), getStatsGroups(), getStatsDB() used by getStats().
• Sampling/maintenance probability per blog/global.
• display_stats is numeric indicating every n requests to sample.
• Isolated admin extension for backend only.

Version 1.1.0 - March 13, 2025

• Change SQLite synchronous from OFF to NORMAL.
• Use insert... on conflict rather than replace.
• Add SQLite mmap_size to enable memory mapped I/O.
• Add SQLite page_size to adjust page size.
• Add SQLite cache_size to adjust cache size.
• Add WITHOUT ROWID when creating table.
• Ensure correct blog id when building key in multisite environment.
• Optimize pre-fetch.
• Export cached transients back to MySql when disabled.
• Requires Sqlite3 version 3.24.0.

Version 1.0.4 - May 24, 2024

• Fix for updated {eac}Doojigger Advanced Mode, remove from 'Tools' tab.

Version 1.0.3 - April 3, 2024

• Added notice if eacDoojigger is not active.
• Delete sqlite file(s) rather than records on flush.
• Set wp_installing and fixed expiration when importing transients,
• switch_to_blog() now flushes L1 and reloads prefetch groups.
• flush_blog() use $this->blog_id instead of get_current_blog_id().
• Suppress flush message when 0 records flushed.
• Use options_form.requestSubmit() instead of options_form.submit().

Version 1.0.2 - February 17, 2024

• Minor updates as per WordPress review team.
• Changed EAC_OBJECT_CACHE to EAC_OBJECT_CACHE_VERSION.
• Added ABSPATH check in wp-cache.php.
• Escape output of calculated cache ratio.

Version 1.0.1 - January 24, 2024

• Improved sanitization and output escaping.
• Changed constant EACDOOJIGGER_OBJECT_CACHE to EAC_OBJECT_CACHE.

Version 1.0.0 - December 9, 2023

• First public release, submitted to WordPress review team.

Version 0.5

• Testing in live, multisite environment.
• Ignore 'force_cache' flag (force L2 read).
• if we've updated a key, but not written yet, then force a persistent load, we lose that value.
• Added wp_flush_blog() function.
• Cache L2 misses saving sqlite selects on records known to not exist.
• Don't attempt read or delete on non-persistent groups.
• Added cache hit ratio to stats.
• Remove function call counts (for testing).

Version 0.4

• Enhanced admin screen with advanced options.
• Group constants used:
• EAC_OBJECT_CACHE_GLOBAL_GROUPS
• EAC_OBJECT_CACHE_NON_PERSISTENT_GROUPS
• EAC_OBJECT_CACHE_PERMANENT_GROUPS
• EAC_OBJECT_CACHE_PREFETCH_GROUPS
• Added non-standard wp_cache_add_permanent_groups(), wp_cache_add_prefetch_groups()

Version 0.3

• Parameterize timeout, retries.
• Import transients from MySQL.
• Rework select/replace/delete SQL.
• New select_one(), select_all() methods.
• key_exists(), key_exists_memory(), key_exists_database() replace _exists().
• Add permanent groups (allow no expiration, overriding default expire).
• Add function call counts (for testing).

Version 0.2

• Support add/get/set/delete _multiple methods (non-standard replace_multiple).
• Add pre-fetch groups.
• Add delayed writes.
• Add settings via defined constants.
• Add more detailed counts/stats.
• Manage install/uninstall, activate/deactivate actions.

Version 0.1

• Simple memory caching with get/set persistent cache supporting wp-cache functions.
• Testing SQLite methods.