Add option to DB if option is only present in cache when updating option

[codix]

In very rare circumstances some options may not be in DB but in cache. On update if updating DB fails remove from cache and try to add option. This would eventually fix cache inconsistencies if they occur.

Both update_option and update_site_option are affected.

[uglyrobot]

I agree that these persistent object cache/db inconsistencies are annoying as heck.

[nacin]

In very rare circumstances some options may not be in DB but in cache.

Knowing under what circumstances this would occur is really the only good way to fix this.

I understand the desire to wp_cache_delete() in these situations, but I am not sure about the desire to re-add. There is a concern that cache is stale, should just work to clear the cache and let it balance itself out later.

This is lacking unit tests to demonstrate the bug and/or fix, so I'm moving it to future release pending additional feedback.

[lukecavanagh]

@chriscct7

I can work on a patch refresh.

[lukecavanagh]

Patch refresh

[juanmaguitar]

From today's bug scrub

I'll keep it for now in 7.0 as if the PR is fine it could still be included in the 7.0 release. I'll ping a Core Comitter to have a look at the PR. I'll be happy to test it when the PR has been approved.

@SergeyBiryukov could you have a look at the PR. If the code is fine I can try to test it.

[audrasjb]

As per today's 7.0 pre-RC1 bug scrub:
As the PR still needs testing, let's move the ticket to 7.1.