Re: hanging for 30sec when checkpointing

On Mon, 9 Feb 2004, Tom Lane wrote:

> "scott.marlowe" <scott(dot)marlowe(at)ihs(dot)com> writes:
> > That said we have a really HUGE (~200 drive) IDE storage array my web /
> > app server sits on top of. No clue if that thing will reliably work under
> > a database, and I'm in no hurry to find out.
>
> > But since the fsync on WAL is all that seems important, I could always
> > initlocation a big chunk of it and keep the WAL local and I should be ok.
>
> Unfortunately not --- at checkpoint time, the constraint goes the other
> way. We have to be sure all the data file updates are down to disk
> before we write a checkpoint record to the WAL log. So you can still
> get screwed if the data-file drive lies about write completion.

Hmmm. OK. Would the transaction size be an issue here? I.e. would small
transactions likely be safer against corruption than large transactions?

I ask because most of the testing I did was with pgbench running 100+
simos (on a -s 100 pgbench database) and as long as the WAL drive was
fsyncing correctly, the database survived.