Re: Enable data checksums by default

On Mon, Apr 1, 2019 at 10:17 AM Christoph Berg <myon(at)debian(dot)org> wrote:

> Re: Tomas Vondra 2019-03-30 <20190330192543(dot)GH4719(at)development>
> > I have not investigated the exact reasons, but my hypothesis it's about
> > the amount of WAL generated during the initial CREATE INDEX (because it
> > probably ends up setting the hint bits), which puts additional pressure
> > on the storage.
> >
> > Unfortunately, this additional cost is unlikely to go away :-(
>
> If WAL volume is a problem, would wal_compression help?
>
> > Now, maybe we want to enable checksums by default anyway, but we should
> > not pretent the only cost related to checksums is CPU usage.
>
> Thanks for doing these tests. The point I'm trying to make is, why do
> we run without data checksums by default? For example, we do checksum
> the WAL all the time, and there's not even an option to disable it,
> even if that might make things faster. Why don't we enable data
> checksums by default as well?
>

I think one of the often overlooked original reasons was that we need to
log hint bits, same as when wal_log_hints is set.

Of course, if we consider it today, you have to do that in order to use
pg_rewind as well, so a lot of people who want to run any form of HA setup
will be having that turned on anyway. I think that has turned out to be a
much weaker reason than it originally was thought to be.

--
Magnus Hagander
Me: https://www.hagander.net/ <http://www.hagander.net/>
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