[development] Counterintuitive but true: Caching makes a high-traffic site slower

[John Handelaar]

In the continuing absence of anywhere to discuss these
performance edge-cases (more below)...


I've already mentioned recently that MyISAM is the
enemy of Drupal performance.  Because it requires a
full-table lock, if you have lots of active members
logged in at once, the process of posting a comment
causes page rendering to cease entirely for several
seconds.

Onto today's point:

The same table-level locking is *lethal* on a heavily-
trafficked site which has both

a)  Content which alters regularly (like a busy forum),
     and

b)  Caching turned on.


Try turning it off if your slow query log starts showing
cache-related things taking 90 seconds (!) or more (!!).

And then take a backup of your database and change these
table types to InnoDB format.

And then start looking at delayed inserts.


jh


PS:  Still no bigsite/performance forum.  Have we decided
that Drupal doesn't *need* to scale?  I missed that meeting.