[wp-trac] [WordPress Trac] #8071: Refrain from querying all the comments on a post when paged

[WordPress Trac]

#8071: Refrain from querying all the comments on a post when paged
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 Reporter:  markjaquith             |       Owner:  boonebgorges
     Type:  enhancement             |      Status:  closed
 Priority:  normal                  |   Milestone:  4.4
Component:  Comments                |     Version:  2.7
 Severity:  normal                  |  Resolution:  fixed
 Keywords:  has-patch dev-feedback  |     Focuses:
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Changes (by boonebgorges):

 * status:  assigned => closed
 * resolution:   => fixed


Comment:

 In [changeset:"34561"]:
 {{{
 #!CommitTicketReference repository="" revision="34561"
 Force comment pagination on single posts.

 Previously, the 'page_comments' toggle allowed users to disable comment
 pagination. This toggle was only superficial, however. Even with
 'page_comments' turned on, `comments_template()` loaded all of a post's
 comments into memory, and passed them to `wp_list_comments()` and
 `Walker_Comment`, the latter of which produced markup for only the
 current page of comments. In other words, it was possible to enable
 'page_comments', thereby showing only a subset of a post's comments on a
 given
 page, but all comments continued to be loaded in the background. This
 technique
 scaled poorly. Posts with hundreds or thousands of comments would load
 slowly,
 or not at all, even when the 'comments_per_page' setting was set to a
 reasonable number.

 Recent changesets have addressed this problem through more efficient tree-
 walking, better descendant caching, and more selective queries for top-
 level
 post comments. The current changeset completes the project by addressing
 the
 root issue: that loading a post causes all of its comments to be loaded
 too.

 Here's the breakdown:

 * Comment pagination is now forced. Setting 'page_comments' to false leads
 to evil things when you have many comments. If you want to avoid
 pagination, set 'comments_per_page' to something high.
 * The 'page_comments' setting has been expunged from options-
 discussion.php, and from places in the codebase where it was referenced.
 For plugins relying on 'page_comments', we now force the value to `true`
 with a `pre_option` filter.
 * `comments_template()` now queries for an appropriately small number of
 comments. Usually, this means the `comments_per_page` value.
 * To preserve the current (odd) behavior for comment pagination links,
 some unholy hacks have been inserted into `comments_template()`. The
 ugliness is insulated in this function for backward compatibility and to
 minimize collateral damage. A side-effect is that, for certain settings of
 'default_comments_page', up to 2x the value of `comments_per_page` might
 be fetched at a time.
 * In support of these changes, a `$format` parameter has been added to
 `WP_Comment::get_children()`. This param allows you to request a flattened
 array of comment children, suitable for feeding into `Walker_Comment`.
 * `WP_Query` loops are now informed about total available comment counts
 and comment pages by the `WP_Comment_Query` (`found_comments`,
 `max_num_pages`), instead of by `Walker_Comment`.

 Aside from radical performance improvements in the case of a post with
 many
 comments, this changeset fixes a bug that caused the first page of
 comments to
 be partial (`found_comments` % `comments_per_page`), rather than the last,
 as
 you'd expect.

 Props boonebgorges, wonderboymusic.
 Fixes #8071.
 }}}

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Ticket URL: <https://core.trac.wordpress.org/ticket/8071#comment:35>
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