From 9877d2cf0bff54f36f257c7a6f69ee934bed45e7 Mon Sep 17 00:00:00 2001
From: Seamus Lee <seamuslee001@gmail.com>
Date: Tue, 16 Jul 2019 12:03:07 +1000
Subject: [PATCH] Resolve #549 Document Long and short cache
---
docs/framework/cache.md | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/docs/framework/cache.md b/docs/framework/cache.md
index 317d1e3d..7b05d7e1 100644
--- a/docs/framework/cache.md
+++ b/docs/framework/cache.md
@@ -68,12 +68,20 @@ configuring the default cache driver, see [System Administrator Guide => Setup =
### Aliases
-In reading code, you may find these three notations -- which all refer to the same thing:
+In reading code, you may find these three notations -- which all refer to the same thing which is essentially a 'short' cache as described below:
* `Civi::cache()`
* `Civi::cache('default')`
* `CRM_Utils_Cache::singleton()`
+## long and short caches
+
+In CiviCRM Codebase there are generally 2 types of caches discussed 'long' and 'short' caches. Both Long and Short caches can be stored in a cache aggregation system such as Memcached or Redis or APC. For most CiviCRM users that do not implement such caching mechanisms, Long caches are stored in the SQL Database in the `civicrm_cache` table and short caches are stored in an ArrayCache which is just a PHP array instance.
+
+When calling code such as `Civi::cache()->` This resolves to the default cache which is an instance of short cache. This basically around about way is the equivalent of calling `CRM_Utils_Cache::create` with the storage `type` parameter set to `['*memory*', 'ArrayCache']` where as calling `Civi::cache('long')->` or `Civi::cache('settings')` or `Civi::cache('session')` as some examples of 'long' caches this sets the storage type to be `['*memory*', 'SqlGroup', 'ArrayCache']`.
+
+By default neither short or long caches use the withArray parameter which would allow some PHP Thread optimisation. This may change in the future however at present to utilisation a PHP arrayCache in front of say Redis or Memcached etc, then the cache would have to be defined with `withArray => TRUE` or `withArray => fast`.
+
## Using a custom cache {:#custom}
Generally, it's best to store caches in a memory-backed service like Redis or Memcached. But what happens if the system-configuration doesn't support that?
--
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