"flush cache" flush all cache on shared redis

[pawawat]

I try setup two wordpress instances and setup unique WP_CACHE_KEY_SALT for each one. When I click "flush cache", plugins flush cache of two instances instead of flushing cache only on that wordpress instance

[tillkruss]

Redis's FLUSHDB command works per database, so you'd need to use different databases for each installation to prevent that from happening.

The alternative, walking through all keys in the database and checking it's prefix isn't performant.

However, if you really need that feature, feel free to submit a PR with a feature flag.