Query-based caches are now improved by reusing cache keys. Previously, cache keys for query caches were generated using the `last_changed` value as part of the key. This meant that whenever `last_changed` was updated, all the previously cached values for the group became unreachable.
The new approach allows WordPress to replace previously cached results that are known to be stale. The previous approach relied on the object cache backend evicting stale keys which is done at various levels of efficiency.
To address this, the following new helper functions have been introduced:
* wp_cache_get_salted
* wp_cache_set_salted
* wp_cache_get_multiple_salted
* wp_cache_set_multiple_salted
These functions provide a consistent way to get/set query caches. Instead of using the last_changed value as part of the cache key, it is now stored inside the cache value as a "salt". This allows cache keys to be reused, with values updated in place rather than relying on eviction of outdated entries.
Props spacedmonkey, peterwilsoncc, flixos90, sanchothefat, tillkruess, rmccue, mukesh27, adamsilverstein, owi, nickchomey.
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WordPress has recently introduced a variety of caching API improvements:
* `wp_cache_add_multiple()`
* `wp_cache_set_multiple()`
* `wp_cache_get_multiple()`
* `wp_cache_delete_multiple()`
* `wp_cache_flush_runtime()`
* `wp_cache_flush_group()`
Although WordPress core provides a compatibility layer if these functions are missing from third-party object cache implementations, there should be a method of checking whether the cache backend supports a particular feature.
This commit aims to improve developer experience by allowing third-party object cache plugins to declare a `wp_cache_supports()` function and correctly list their supported features:
* `add_multiple`
* `set_multiple`
* `get_multiple`
* `delete_multiple`
* `flush_runtime`
* `flush_group`
Note: The `wp_cache_supports()` function replaces and supersedes the `wp_cache_supports_group_flush()` function added earlier.
Follow-up to [47938], [47944], [52700], [52703], [52706], [52708], [53763], [53767], [54423].
Props johnjamesjacoby, tillkruess, spacedmonkey, SergeyBiryukov.
Fixes#56605.
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Includes:
* Placing `WP_Object_Cache::flush_group()` next to `::flush()`.
* Placing `wp_cache_supports_group_flush()` next to `wp_cache_flush_group()`.
* Placing the `wp_cache_flush_group()` unit test next to the `::flush()` method test.
* Removing test name from assertion messages, as it is already mentioned directly above in case of failure.
* Adjusting function descriptions per the documentation standards.
Follow-up to [52706], [53763].
See #55647, #4476.
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Add a new plugable function called `wp_cache_flush_group`, that will allow developers to clear whole cache groups with a single call. Developers can detect if their current implementation of an object cache supports flushing by group, by calling `wp_cache_supports_group_flush` which returns true if it is supported. If the developers of the object cache drop-in has not implemented `wp_cache_flush_group` and `wp_cache_supports_group_flush`, these functions are polyfilled and `wp_cache_supports_group_flush` defaults to false.
Props Spacedmonkey, filosofo, ryan, sc0ttkclark, SergeyBiryukov, scribu, Ste_95, dd32, dhilditch, dougal, lucasbustamante, dg12345, tillkruess, peterwilsoncc, flixos90, pbearne.
Fixes#4476.
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Add a new function called `wp_cache_flush_runtime` to existing caching functions found in WordPress. This function allows users to flush the runtime (in-memory) cache, without flushing the entire persistent cache.
Props: Spacedmonkey, tillkruess, flixos90, adamsilverstein, SergeyBiryukov, barryhughes.
Fixes: #55080.
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The original order was alphabetical, which became less obvious as newer functions got added, resulting in a somewhat random order.
This commits aims to organize the functions and related `WP_Object_Cache` methods in a more predictable order:
* `wp_cache_init()`
* `wp_cache_add()`
* `wp_cache_add_multiple()`
* `wp_cache_replace()`
* `wp_cache_set()`
* `wp_cache_set_multiple()`
* `wp_cache_get()`
* `wp_cache_get_multiple()`
* `wp_cache_delete()`
* `wp_cache_delete_multiple()`
* `wp_cache_incr()`
* `wp_cache_decr()`
* `wp_cache_flush()`
* `wp_cache_close()`
* `wp_cache_add_global_groups()`
* `wp_cache_add_non_persistent_groups()`
* `wp_cache_switch_to_blog()`
* `wp_cache_reset()`
Follow-up to [3011], [6543], [7986], [13066], [18580], [21403], [47938], [52700], [52703-52705].
See #54728, #54574.
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Add new caching functions named `wp_cache_add_multiple`, `wp_cache_set_multiple` and `wp_cache_delete_multiple`. All of these functions allow for an array of data to be passed, so that multiple cache objects can be created / edited / deleted in a single function call. This follows on from [47938] where the `wp_cache_get_multiple` function was introduced and allowed for multiple cache objects to be received in one call.
Props: spacedmonkey, tillkruess, adamsilverstein, flixos90, mitogh, pbearne.
Fixes: #54574.
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