Re: Risk of data corruption/loss?

On Wed, Mar 13, 2013 at 8:24 AM, Niels Kristian Schjødt <
nielskristian(at)autouncle(dot)com> wrote:

> I'm considering the following setup:
>
> - Master server with battery back raid controller with 4 SAS disks in a
> RAID 0 - so NO mirroring here, due to max performance requirements.
> - Slave server setup with streaming replication on 4 HDD's in RAID 10. The
> setup will be done with synchronous_commit=off and
> synchronous_standby_names = ''
>

Out of curiosity, in the presence of BB controller, is
synchronous_commit=off getting you additional performance?

> So as you might have noticed, clearly there is a risk of data loss, which
> is acceptable, since our data is not very crucial. However, I have quite a
> hard time figuring out, if there is a risk of total data corruption across
> both server in this setup? E.g. something goes wrong on the master and the
> wal files gets corrupt. Will the slave then apply the wal files INCLUDING
> the corruption (e.g. an unfinished transaction etc.), or will it
> automatically stop restoring at the point just BEFORE the corruption, so my
> only loss is data AFTER the corruption?
>

It depends on where the corruption happens. WAL is checksummed, so the
slave will detect a mismatch and stop applying records. However, if the
corruption happens in RAM before the checksum is taken, the checksum will
match and it will attempt to apply the records.

Cheers,

Jeff