Multisite option caching breaks for sites with bigger options

[pavelschoffer]

This change (https://core.trac.wordpress.org/ticket/37181) changed the way multisite options are retrieved and cached in trunk (to be released in 6.1.).

The old code used to put to cache each requested site meta (=network option) separately under a key: <network_id>:<option_key> so for example 1:site_name.

The new code fetches all the options for the given network_id (not just the one you are asking for) and saves the whole set of them under one key :site_meta:<network_id> so :site_meta:1. Where the value in the cache would be:

{
   "site_name": '...',
   "option2", '...',
   ...
}

The outcome of this change is that if the cumulative size of ALL site options is bigger than 1MB (default limit of memcached per object) NONE of the options will be cached.

Would it be possible to revert the change and/or make the cache key per-site versus per-site-and-option-key optional?

[rebasaurus]

The outcome of this change is that if the cumulative size of ALL site options is bigger than 1MB (default limit of memcached per object) NONE of the options will be cached.

If none of the options end up being cached, it will attempt to add them to the cache on each request (e.g. if it never succeeds, it will continue to do so over and over). A sample stacktrace would be:

get_network_option() -> get_metadata_raw() -> update_meta_cache() -> wp_cache_add_multiple() -> wp_cache_add() -> MemcachePool->add()

[johnbillion]

Another concern is that upon updating to 6.1, all existing network option caches will be invalidated because the cache key has changed. That might cause a stampede on sites that are caching a lot of data in network options.

[davidbaumwald]

Revert patch

https://core.trac.wordpress.org/ticket/56845

PR to test GHA to ensure the revert works.

[desrosj]

Marking as first commit review.

[davidbaumwald]

In 54637:

Networks and Sites: Revert the use of the metadata API for *_network_options functions.

[54080] refactored the logic in get_network_option(), update_network_option() and delete_network_option() to use the metadata API. However, this change resulted in issues with large multisite installs that utilize memcached having network options > 1MB in size.

This change reverts [54080] and all related follow-up changes.

Reverts [54080], [54081], and [54082]. Partially reverts [54267] and [54402].

Props pavelschoffer, rebasaurus, johnbillion, spacedmonkey, desrosj, rinatkhaziev.
Fixes #56845.
See #37181.

Merged into core in https://core.trac.wordpress.org/changeset/54637.

[peterwilsoncc]

This change was mentioned in the ​multisite dev note that ought to be followed up:

• a brief dev-note (one or two paragraph) to note it's been reverted
• update the original dev note