Re: Remove fsync ON/OFF as a visible option?

On 2015-03-21 13:53:47 -0700, Josh Berkus wrote:
> Coincidentally, I am just at this moment performance testing "running
> with scissors mode" for PostgreSQL on AWS. When intentional, this mode
> is useful for spinning up lots of read-only replicas which are intended
> mainly as cache support, something I've done at various dot-coms.

Which is where fsync=off barely has any effect?

> So, -1 on removing the setting; it is useful to some users.

Agreed on that.

> Further, full_page_writes=off is supposedly safe on any copy-on-write
> filesystem, such as ZFS.

FWIW, I think that's a myth. One I heard various versions of by now. As
long as the OSs page size (4kb nearly everywhere) is different from
postgres' (8kb) you can have torn pages. Even if individual filesystem
page writes are atomic.

> The proposal that we make certain settings "only available via ALTER
> SYSTEM" also doesn't make sense; ALTER SYSTEM isn't capable of writing
> any settings which aren't available in postgresql.conf.

+1. I think it's a pretty absurd sugestion.

Greetings,

Andres Freund

--
Andres Freund http://www.2ndQuadrant.com/
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