Boone Gorges 60cf073672 Improve WP_Query lazyloading logic, for better performance. ...

Lazyloading for comment meta and term meta, introduced into `WP_Query` in
4.4, used flags - `updated_term_meta_cache` and `updated_comment_meta_cache` -
in an attempt to prevent cache priming from happening more than once per query
object. This technique was mostly effective, but not entirely efficient, since
the flag didn't prevent the `lazyload_*_meta` callbacks from running. The
obvious solution - removing the filter callback after it'd be run once - was
dismissed for 4.4 because of concerns that `remove_filter()` could disable
lazyloading too generally in the context of nested queries, due to the way
`_wp_filter_build_unique_id()` doesn't always build sufficiently unique IDs for
similar objects. However, further testing shows that this concern is only valid
in a very small subset of cases, while the cost of keeping the query objects in
memory, via the `$wp_filter` global, is quite significant. As such, this
changeset removes the flags in favor of the `remove_filter()` technique.

See #35454, #35816.
Built from https://develop.svn.wordpress.org/trunk@36524


git-svn-id: http://core.svn.wordpress.org/trunk@36491 1a063a9b-81f0-0310-95a4-ce76da25c4cd

2016-02-13 03:05:27 +00:00

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