Set_blog_id performance

[wladwm]

On multisite many plugins switches blog (wbdb->set_blog_id) many times (few thousands).
There is a performance impact in wpdb->tables method.
Simple caching reduces overall execution time.

https://core.trac.wordpress.org/ticket/54479#ticket

Add tables names caching for multisite in wpdb->set_blog_id to improved performance with blogs switching.

Trac ticket: https://core.trac.wordpress.org/ticket/54479

[johnbillion]

Thanks for the PR @wladwm! And welcome.

Could you share some before and after performance numbers please? Would be good to see what impact this has.

Cheers

[wladwm]

Hi johnbillion.

On some pages delay for example was reduced from 5.92sec to 5.17sec.
But with some plugin I even cant open some pages w/o patch - cloudfare timeout occurs.
I did some debugging yesterday when discovered this issue with massive blog switching:

[flixos90]

Thank you for raising this @wladwm.

This change seems like a reasonable small performance win. Milestoning this for 6.9, since it already has a PR.

[SirLouen]

I can't see any performance testing and no ​performance use case apart from that image that was retired 4 years ago.

I think this is required, as @johnbillion pointed out back in the day, to see how real impact with numbers.

[khoipro]

I think the Performance team should take care of this change: review and see benchmark. It should be a little bit better, but we can consider to complete fix or retire it.

[westonruter]

Added a review to the PR. I agree that we should get some benchmarks on what impact this change has.

[welcher]

This was reviewed in the bug scrub today. We're getting very close tot he beta 1 cut off, do we think the PR can be refreshed in time?

[westonruter]

Punting to future release since beta1 is next week and the patch still needs refreshing.