wp_suspend_cache_addition should also disable cache setting?

[malthert]

Right now wp_suspend_cache_addition is only checked when "add" to cache.

However most plugins/developers only use wp_cache_set for updating/adding to the cache.
This means in most plugins/cases, wp_suspend_cache_addition has no use, in fact it's rather unexpected behavior that only some functions can add to cache (namely: set, incr, decr)

I propose we also check wp_suspend_cache_addition before setting the cache.
This would also be in line with its function description:

Stops more data being added to the cache, but still allows cache retrieval.

As "set" also "adds" (or at least modifies if already exists therefore adds/subtracts) data in cache.

Fixes: https://core.trac.wordpress.org/ticket/55999

[johnbillion]

This is a good idea but it is a breaking change. During a large import for example, suspending cache addition makes sense to avoid consuming a large amount of memory (particularly when inserting terms and post meta), but updating existing cache entries may well be desirable and expected.

I'll see if I can find some concrete examples.

I think to avoid backwards compatibility issues this needs to be implemented via a new function such as wp_suspend_cache_changes().

Either way, it would be good to get test coverage on this too.