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I have a problem with extreme slow database queries that make my site loading for more than a minute. I am not able to locate the source of that problem. I'm using devel to control the queries and I found out that mostly the functions saving or updating the cache or session tables are the cause. Here is one example of devel's output:

19622.34 1 _drupal_session_write P A UPDATE users SET access=:db_update_placeholder_0 WHERE (uid = :db_condition_placeholder_0)
10442.86 2 DrupalDatabaseCache::clear P A DELETE FROM cache_bootstrap WHERE (cid = :db_condition_placeholder_0)

I do not have an idea what I could do to find the cause of that problem.

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  • Did you consider using caching modules like Memcache, Boost, APC, and Varnish that will help you alot in solving this slow queries which is a known Drupal 7 issue. See these links: (drupal.org/node/97347) (groups.drupal.org/node/21897) (drupalwatchdog.com/1/1/performance-scalability-drupal-7)
    – ninjascorner
    Commented Jun 2, 2012 at 5:53
  • Is the problem intermittent or on every page load?
    – Citricguy
    Commented Jun 3, 2012 at 0:56
  • @Citricguy: The strange thing is, that this problem occurs almost every time but not every time the page is loaded. @ ninjascorner: Thank you for this advice. But I think that this problem must have an other cause. I have two server with the same Drupal installation and almost the same database but this problem occurs only with one of them. I am wandering whether this could have something to do with an encoding issue. I had some strange errors trying to create some nodes that contain UTF8 encoded text before...
    – user5950
    Commented Jun 4, 2012 at 8:32
  • Do you have cron configured and running? I had a very similar performance issue that was fixed by configuring cron. Tasks were piling up and causing painfully slow page loads on a very regular basis.
    – Citricguy
    Commented Jun 6, 2012 at 4:41
  • Tank you guys for your help. Finally I found out the the vServer was screwed up. I had to contact the hoster and know every thing works fine again. Thank to you I learned much about performance!
    – user5950
    Commented Jun 7, 2012 at 11:03

2 Answers 2

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When a server's I/O performance (especially its disk write performance) reaches its limit, it'll probably show first with cache queries because they're frequent and can contain some quite big chunks of serialized data.

I recommend you take a look at your disk I/O while you're waiting for a page to render, by using iotop for example.

The best way to prevent those I/O bottlenecks is to keep page requests from even reaching Drupal by putting a Varnish cache in front of the webserver. If they need to be answered by Drupal, though, at least take the cache load from the database by using Memcache.

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Look at this answer I recently gave: Do Drupal websites have bad performance or are heavy? In short you might need to tune MySQL a little bit. What does SHOW VARIABLES LIKE 'innodb_buffer_pool_size' say?

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  • MY site is vey sloe, and SHOW VARIABLES LIKE 'innodb_buffer_pool_size' says 1. What does that mean? What can I do?
    – Dev
    Commented Sep 21, 2016 at 13:13
  • @Drupaler that's not a valid number for that variable dev.mysql.com/doc/refman/5.6/en/…
    – mikeytown2
    Commented Sep 21, 2016 at 15:29

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