Speeding up Dashboard and Comment moderation SQL load
|Reported by:||FolioVision||Owned by:||markjaquith|
|Severity:||major||Keywords:||has-patch 2nd-opinion needs-testing|
The standard Wordpress function for counting the comments for Admin Bar and Dashboard named wp_count_comments is using a single SQL query with GROUP BY clause. That makes it slow on a large site with hundreds of thousands of comments.
SELECT comment_approved, COUNT(*) AS num_comments FROM wp_comments GROUP BY comment_approved;
This takes 0.3 seconds on our site with 400,000 comments. When there are 10 editors logged in, we can see increasing server load.
Our solution is to run 5 faster queries instead:
SELECT COUNT( comment_ID ) FROM wp_comments WHERE comment_approved = 'trash' SELECT COUNT( comment_ID ) FROM wp_comments WHERE comment_approved = 'spam' SELECT COUNT( comment_ID ) FROM wp_comments WHERE comment_approved = '0' SELECT COUNT( comment_ID ) FROM wp_comments WHERE comment_approved = 'post-trash' SELECT COUNT( comment_ID ) FROM wp_comments
Takes 0.042144 on the same site. The last query gets the number of all the comments, then we subtract the previous query totals to get number of approved comments.
On a database of 4 million comments the difference is 1.52 seconds for the original wp_count_comments and 0.01 seconds for our alternative count with 5 queries.
Here is a link to our quick piece of code which hooks to the required filter hook and replaces the original slow function wp_count_comments: http://foliovision.com/downloads/fv_wp_count_comments.php.txt
But this is a hack - it would be much better to fix this in core by replacing the existing slow queries with 5 fast ones and subtraction to get total approved comments.
This speedup can be very important on large sites, as often there are 10 or more writers and moderators working at the same time. What can happen with the existing code is that the slow count comments query can back up MySQL and then writers can no longer save or open posts to edit. They get very, very frustrated and even angry.
This fix will allow Wordpress to scale much larger on relatively modest hardware (no separate MySQL dual quad server).
Thanks for listening.
Change History (17)
- Keywords needs-patch added; wp_count_comments sql dashboard speed performance removed
- Milestone changed from Awaiting Review to 3.4
- Keywords has-patch 2nd-opinion needs-testing added; needs-patch removed
- Severity changed from critical to major