Re: Sv: Re: Sv: Re: Sv: Re: Sv: Re: data-checksums

Greetings,

* Andreas Joseph Krogh (andreas(at)visena(dot)com) wrote:
> Aha, so enabling CRC causes hint-bits to be written causing extra WAL-logging,
> which woudn't be the case without CRC enabled?
> Thanks for pointing that out.

Yes, having checksums enabled forces logging of hint bits. You can
enable wal_log_hints independently too, without having checksums, to see
what kind of an impact it'll have on your environment.

A useful documentation update might be:

---
With checksums enabled, wal_log_hints <link to the GUC's documentation>
will be enabled and each page read or write will involve calculating the
checksum for the page.
---

I'd probably just replace the "Enabling checksums may incur a noticeable
performance penalty" with the above, as it should be clear that doing
more work implies an impact on performance and that avoids the whole
question of trying to characterize in a general way something that can't
be generalized (as it's workload dependent).

Thanks!

Stephen