On Wed, Nov 17, 2010 at 12:49 PM, Josh Berkus <j...@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. >> > > That's a nice thought, but it's not how data corruption works in the event > of a crash. If a table is corrupted, *we don't know* how it's corrupted, > and it's not just "the last few records" which are corrupted. So for > unlogged tables, there is never going to be any other option for crashes > than to truncate them. > > 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 > > -- > -- Josh Berkus > PostgreSQL Experts Inc. > http://www.pgexperts.com > > -- > Sent via pgsql-general mailing list (pgsql-general@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-general >
