The feature added in 4.1 to lock the modinfo cache does not work when
using Redis, because:
* The API to acquire a cache lock is confusing, and the code did not
check that it successfully acquired a lock before going on to build
the cache anyway.
* Unlike the other types of cache lock, the Redis store did not retry
the lock for a timeout period before giving up and failing.
This change fixes both points.
In some cases, we get an error message such as:
Wrong parameter count for Redis::zRem()
Within the delete_many function. This function requires at least one
key to be supplied, but if delete_many is called with an empty array,
we will call it with no keys.
The Redis cache store and session handler both do a 'ping()' after
connecting to Redis. This is unnecessary because the connect() call
has just checked the network connection and it's hardly likely that
the server has gone down since then.
According to my profiling, both connect() and ping() take
measurable time when talking to a separate server, i.e. a few
milliseconds. So it's not the case that connect() doesn't really
talk to the server, as I initially wondered.
If using Redis on a separate (non-localhost) server for both session
and cache store, removing these ping calls can save a millisecond
or two per request.
When deleting a cache instance, it tried to purge it, even though
purge only makes sense for an individual definition (not the whole
instance). As a result, it errored.
For cache types which mean this information can be obtained without a
significant performance cost (i.e. just by calling strlen and not
having to serialize something that wasn't serialized already),
this change calculates the size of data read from or written to cache
in each request and includes it in the perfdebug table at bottom of
output (when that is turned on).
This supports the following cache types:
* File store
* Redis (only if caching is enabled)
A list of times for each cache key in a TTL cache is kept in a Redis
sorted list, which can be queried efficiently to delete expired
cache items later in a scheduled task.
This change makes set and delete 2x slower (only for caches which use
TTL) but there is no impact on get performance.
Due to some changes in Redis 5 php extension Moodle fails to connect via TCP when
no port is set. It's fixed upstream in phpredis repo (version 5.0.0, 5.0.1 and
5.0.2 affected so far), but with this patch we'll send the right port anyway.
This code was originally taken from; https://github.com/durana/moodle-cachestore_redis
Special thanks to Mark Nielsen and Adam Durana for their work on this.
Since the original import;
- Mode session support has been added.
- Some cleanup of names has been made.
- Data guarantee and references support was added.
Srdjan