On Wed, Nov 17, 2010 at 12:49 PM, Josh Berkus
<josh@agliodbs.com> wrote:
As was already mentioned, application logs. Unlogged tables would be
perfect for that, provided they don't go *poof* every now and then for
no good reason. Nobody's going to be too heart broken if a handful of
log records go missing, or get garbled, after a server crash or power
outage. Delete 'em all after every restart though, and that's a problem.
Robert Haas did discuss the ability to synch unlogged tables on a planned shutdown, though. However, that's liable to wait until 9.2, given the multiple steps required to make it work.
Note that you would have the option of periodically synching an unlogged table to pgdump or to a logged table, via script, if you cared about retaining the data. That would probably give you the behavior you want, above.
In an airplane, a pilot can kill the engine mid-flight if [s]he wants to. They can deploy the flaps /slats at cruise speed / altitude, and if they're so minded, they can land with a full tank of gas. Now, none of these things are particularly wise, but that's why the pilots are given *slightly* more learning than your average bus driver.
If you want to have a widely usable 'unlogged' table feature, I highly recommend that 'truncate on server crash/restart' be an option that is defaulted to true. That way, I can go in an push the buttons I want and give corrupted data to whomever, whenever i like. (Land with a full tank of Jet-A).
Whatever the decision is about backup, doesn't really matter IMO, but I honestly think that the benefit of an unlogged table is there for both session data (I run my session db's in fsync mode anyway and re-initdb them on boot) AND for logging data where I can't take WAL anymore, but would like to be able to have them in the same cluster as other stuff. If they just disappear then this feature won't be useful [to me] and I'll have to either wait for the patch or give up on it and do a flat-file / lucene project just to deal with it (I really don't want to do that :-).
--Scott
