Memory exhaustion caused by very many unattached media

[andy]

A blog with over 30,000 unattached images was exhausting available memory on unattached attachment pages. The exhaustion occurred in previous_image_link() -> adjacent_image_link() -> get_children() due to the large number of rows selected with post_parent=0.

This is not the only place where get_posts() might be called with post_parent=0. A similar query appears in twentythirteen_the_attached_image() but the effect is wisely mitigated by fields=ids. Earlier, twentyten/loop-attachment.php called get_children() with post_parent=0 on unattached image pages which is horribly inefficient when there are many unattached images.

Attached patch depends on #24687. The change to adjacent_image_link() creates a MySQL query which selects only the desired row. This fixes the memory exhaustion error on the blog with 30,000 unattached images. The once-only filters would be unnecessary if WP_Query accepted arbitrary extra WHERE strings.

[SergeyBiryukov]

Related: #23044

[SergeyBiryukov]

Related: [7222]

[wonderboymusic]

these are all marked 3.7-early

[ocean90]

Punting due to lack of testing.

[ericlewis]

Replying to andy:

The once-only filters would be unnecessary if WP_Query accepted arbitrary extra WHERE strings.

That's interesting. Are you subtly proposing this idea?

[kitchin]

About the patch return "$where AND (... should be return "( $where ) AND (... There are operators that bind less tightly, like OR.

Is that what you meant by testing? :)

[andy]

I think since #26042 is closed this ticket now just needs a new patch and testing.

[dllh]

Updated patch

[dllh]

I've updated the patch for trunk and given it a test drive. It seems to work well for me. Any chance of nudging this along?

[kitchin]

My objection above still stands, to $where without parentheses in return "$where AND ...