WP is asking for comment count for post 0

[Grzegorz.Janoszka]

In wp-includes/comment.php we have a function wp_count_comments defined:
function wp_count_comments( $post_id = 0 )
so by default $post_id is 0.
Later on in the function we query the cache:
$count = wp_cache_get( "comments-{$post_id}", 'counts' );

We shouldn't query the cache for such number if post_id is 0 as we will never get a value from the cache, so I suggest adding "if ($post_id) then" before querying the cache. It might be that more of this function code should be included in such if, being void for post_id equal to 0 (and there are such calls).

[soulseekah]

The docblock does not explicitly state this, but calling wp_count_comments and get_comment_count with 0 (or no argument) returns the totals for the whole blog, so caching seems to actually be valid here.

[Grzegorz.Janoszka]

Ah, a pity it was not in the docs that post_id=0 means all comments for the blog.
I hope it will be fixed.
And I haven't noticed counts was non-persistent group, so actually each WP page load generates cache miss for this one.
I am closing this ticket now.

[soulseekah]

The docblock should be fixed, I think to avoid such confusion in the future. Reopening.

[SergeyBiryukov]

Replying to soulseekah:

The docblock does not explicitly state this, but calling wp_count_comments and get_comment_count with 0 (or no argument) returns the totals for the whole blog, so caching seems to actually be valid here.

It looks like this was addressed in [46223] / #47110, both functions mention it in the DocBlock now:

@param int $post_id Optional. Restrict the comment counts to the given post. Default 0, which indicates that
                    comment counts for the whole site will be retrieved.