Re: hanging for 30sec when checkpointing

"scott.marlowe" <scott.marlowe@ihs.com> writes:
>> 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?

Transaction size would make no difference AFAICS.  Reducing the interval
between checkpoints might make things safer in such a case.

> 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.

Did you try pulling the plug immediately after a CHECKPOINT command
completes?  You could test by manually issuing a CHECKPOINT while
pgbench runs, and yanking power as soon as the prompt comes back.

            regards, tom lane