slow down website performance

Hint: Take a look at the output of:
SELECT * FROM wp_options WHERE option_name = 'cron'\G

If you’re issue is anything like ours, you probably have tens of thousands of dsq_sync_forum cron jobs schedule – one triggered every page hit, 5 minutes from when it was hit. At some point, you won’t be able to clear the jobs quickly enough, and your website will be brought to its knees.

Maybe try this patch (which I’m currently in the process of testing):

Index: disqus.php
===================================================================
--- disqus.php	(revision 1214695)
+++ disqus.php	(working copy)
@@ -511,7 +511,9 @@
                     }
                 } else {
                     $ts = time() + 300;
-                    wp_schedule_single_event($ts, 'dsq_sync_forum');
+                    if (!wp_next_scheduled('dsq_sync_forum')) {
+                        wp_schedule_event($ts, 'hourly', 'dsq_sync_forum');
+                    }
                     die('// sync scheduled');
                 }
             break;

That should slow down the Disqus syncs to one per hour max, which I imagine is more than enough.

The Disqus devs wouldn’t accept a PR because they don’t want everyone running low traffic websites to have their blog hit the Disqus servers every hour if they didn’t even receive any hits. That’s a fair point, but it sucks for high-traffic websites that are getting destroyed in the meantime (and probably hurting the Disqus servers more overall anyway). I’m quite amazed they haven’t addressed the issue themselves by now, given they now know their plugin is causing big issues for people using it.

Having said that, I don’t think the above approach was completely reliable. I think this may have been related to a conflict somewhere with W3 Total Cache, but didn’t spend more time than necessary investigating.

In the end, I commented out the entire sync_comments case statement section from disqus.php, and modified scripts/import-comments.php to write to syslog instead of stdout. I then call that import-comments.php script directly via a cron job on one (and only one) of our app servers. I also had to comment out the unused DummyWP_Object_Cache class from lib/wp-cli.php for this to work properly. This approach seems to be working quite well.