On 10/15/06, mark@mark.mielke.cc <mark@mark.mielke.cc> wrote:
> Using memcache, I've had problems with consistency brought right to
> the front. Both of these have failed me:
>
> 1) When updating a PostgreSQL record, I invalidate the memcache record.
> If another process comes along in parallel before I commit, notices
> that the memcache record is invalidated, it queries the data from
> SQL, and updates the memcache record back to the old value. :-(
>
> 2) When updating a PostgreSQL record, I updated the memcache record
> to the new value. If another process comes along in parallel before
> I commit, that is still looking at an older view, cross-referencing
> may not work as expected.
>
> I'm currently settled on 2), but setting a short timeout (5 seconds) on
> the data. Still an imperfect compromise between speed and accuracy, but
> it isn't causing me problems... yet.
use advisory locks for 'race sensitive' data. (or user locks in <
8.2). or, just use tables, becuase you need mvcc, not performance :)
merlin