id,summary,reporter,owner,description,type,status,priority,milestone,component,version,severity,resolution,keywords,cc
16894,Bulk load Comment Meta upon access,dd32,,"When we query posts, we bulk load all of the posts meta and taxonomies at the time of request. Since adding comment meta, we load the comment meta on-the-fly since nothing really currently uses it in core.

I've added a filter to ''get_comment_text'' which modifies the comment content based on the value of a meta key.

The problem arises when multiple comments are displayed on a page, The metadata for every comment is loaded individually:

{{{
SELECT comment_id, meta_key, meta_value FROM wp_commentmeta WHERE comment_id IN (4)
SELECT comment_id, meta_key, meta_value FROM wp_commentmeta WHERE comment_id IN (5)
SELECT comment_id, meta_key, meta_value FROM wp_commentmeta WHERE comment_id IN (6)
SELECT comment_id, meta_key, meta_value FROM wp_commentmeta WHERE comment_id IN (7)
SELECT comment_id, meta_key, meta_value FROM wp_commentmeta WHERE comment_id IN (34)
SELECT comment_id, meta_key, meta_value FROM wp_commentmeta WHERE comment_id IN (35)
SELECT comment_id, meta_key, meta_value FROM wp_commentmeta WHERE comment_id IN (37)
}}}

in all cases, the function stack is:
{{{
comments_template, wp_list_comments, Walker->paged_walk, Walker_Comment->display_element, Walker->display_element, call_user_func_array, Walker_Comment->start_el, call_user_func, twentyten_comment, comment_text, get_comment_text, apply_filters, call_user_func_array, MY_FUNCTION_HOOKED_TO_GET_COMMENT_TEXT, get_comment_meta, get_metadata, update_meta_cache #12 (0.7ms)
}}}

It isn't ideal that every comment causes an extra query, instead, we should bulk load comment meta for the comments being displayed. 

However, Since comment meta is not always used, in order to keep the load down, I'd suggest that we only bulk load the comment meta '''on the first request for comment meta''', this should allow current users to have no detrimental affect on query count/performance, whilst allowing those who use comment meta to manage each comment better performance.",defect (bug),new,normal,Future Release,Performance,3.1,normal,,needs-patch 2nd-opinion,