Re: Postgres, fsync, and OSs (specifically linux)

On 15 August 2018 at 07:32, Thomas Munro <thomas.munro@enterprisedb.com>
wrote:

> On Wed, Aug 15, 2018 at 11:08 AM, Asim R P <apraveen@pivotal.io> wrote:
> > I was looking at the commitfest entry for feature
> > (https://commitfest.postgresql.org/19/1639/) for the most recent list
> > of patches to try out.  The list doesn't look correct/complete.  Can
> > someone please check?
>
> Hi Asim,
>
> This thread is a bit tangled up.  There are two related patchsets in it:
>
> 1.  Craig Ringer's PANIC-on-EIO patch set, to cope with the fact that
> Linux throws away buffers and errors after reporting an error, so the
> checkpointer shouldn't retry as it does today.  The latest is here:
>
> https://www.postgresql.org/message-id/CAMsr%2BYFPeKVaQ57PwHqmRNjPCPABsdbV%
> 3DL85he2dVBcr6yS1mA%40mail.gmail.com
>
> 2.  Andres Freund's fd-sending fsync queue, to cope with the fact that
> some versions of Linux only report writeback errors that occurred
> after you opened the file, and all versions of Linux and some other
> operating systems might forget about writeback errors while no one has
> it open.
>
> Here is the original patchset:
>
> https://www.postgresql.org/message-id/20180522010823.
> z5bdq7wnlsna5qoo%40alap3.anarazel.de
>
> Here is a fix-up you need:
>
> https://www.postgresql.org/message-id/20180522185951.
> 5sdudzl46spktyyz%40alap3.anarazel.de
>
> Here are some more fix-up patches that I propose:
>
> https://www.postgresql.org/message-id/CAEepm%3D2WSPP03-20XHpxohSd2UyG_
> dvw5zWS1v7Eas8Rd%3D5e4A%40mail.gmail.com
>
> I will soon post some more fix-up patches that add EXEC_BACKEND
> support, Windows support, and a counting scheme to fix the timing
> issue that I mentioned in my first review.  I will probably squash it
> all down to a tidy patch-set after that.
>


Thanks very much Tomas.

I've had to back off from this a bit after posting my initial
panic-for-safety patch, as the changes Andres proposed are a bit out of my
current depth and time capacity.

I still think the panic patch is needed and appropriate, but agree it's not
*sufficient*.