[wp-trac] [WordPress Trac] #51469: Use `_prime_post_caches` for speeding up cached `get_pages` call

[WordPress Trac]

#51469: Use `_prime_post_caches` for speeding up cached `get_pages` call
-------------------------------+-----------------------------
 Reporter:  david.binda        |      Owner:  (none)
     Type:  enhancement        |     Status:  new
 Priority:  normal             |  Milestone:  Awaiting Review
Component:  Posts, Post Types  |    Version:
 Severity:  normal             |   Keywords:
  Focuses:  performance        |
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 The `get_pages` function uses a cache containing ID of pages matching
 params of a [https://core.trac.wordpress.org/browser/trunk/src/wp-
 includes/post.php?rev=49086#L5683 previous call].

 The IDs are, on a subsequent call with the same params, inflated using the
 [https://core.trac.wordpress.org/browser/trunk/src/wp-
 includes/post.php?rev=49086#L5487 get_post function call]. This works well
 in terms of the same request, as all the pages were previously added to
 [https://core.trac.wordpress.org/browser/trunk/src/wp-
 includes/post.php?rev=49086#L5660 the in-memory cache].

 However, on a subsequent request, when the cache is hit, there are likely
 no pages already in the in-memory cache, and those need to be fetched from
 the backend cache server, one by one.

 With the new `wp_cache_get_multiple`, sites with persistent cache backend
 could improve the speed in such cases, in case the code used the
 `_prime_post_caches` (which internally uses the `_get_non_cached_ids`
 function, which is taking advantage of the mentioned
 `wp_cache_get_multiple`).

 But also sites without a persistent cache backend could benefit from the
 bulk SQL query constructed by the `_prime_post_caches` function, instead
 of fetching each page via individual SQL query.

 The performance gains should be most noticeable in case a site has a lot
 of pages which are being requested via `get_pages` function.

 IMHO, a `_prime_post_caches( $cache, false, false );` should be used to
 match the behaviour of the `get_pages` function
 [https://core.trac.wordpress.org/browser/trunk/src/wp-
 includes/post.php?rev=49086#L5660 when the pages are obtained from the
 database] (thus, no post meta, nor taxonomies priming).

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Ticket URL: <https://core.trac.wordpress.org/ticket/51469>
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