Re: subscriptionCheck failures on nightjar

From: Andres Freund <andres(at)anarazel(dot)de>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: subscriptionCheck failures on nightjar
Date: 2019-02-13 18:33:03
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On 2019-02-13 13:24:03 -0500, Tom Lane wrote:
> Andres Freund <andres(at)anarazel(dot)de> writes:
> > On 2019-02-13 12:59:19 -0500, Tom Lane wrote:
> >> Perhaps more to the point, the way this was coded, the PANIC applies
> >> to open() failures in fsync_fname_ext() not just fsync() failures;
> >> that's painting with too broad a brush isn't it?
> > That indeed seems wrong. Thomas? I'm not quite sure how to best fix
> > this though - I guess we could rename fsync_fname_ext's eleval parameter
> > to fsync_failure_elevel? It's not visible outside fd.c, so that'd not be
> > to bad?
> Perhaps fsync_fname() should pass the elevel through as-is, and
> then fsync_fname_ext() apply the data_sync_elevel() promotion only
> to the fsync() call not the open()? I'm not sure.

Yea, that's probably not a bad plan. It'd address your:

> The bigger picture here is that there are probably some call sites where
> PANIC on open() failure is appropriate too. So having fsync_fname[_ext]
> deciding what to do on its own is likely to be inadequate.

Seems to me we ought to do this regardless of the bug discussed
here. But we'd nee dto be careful that we'd take the "more severe" error
between the passed in elevel and data_sync_elevel(). Otherwise we'd end
up downgrading errors...

> If we fix this by allowing ENOENT to not be an error in this particular
> call case, that's going to involve an fsync_fname_ext API change anyway...

I was kinda pondering just open coding it. I am not yet convinced that
my idea of just using an open FD isn't the least bad approach for the
issue at hand. What precisely is the NFS issue you're concerned about?

Right now fsync_fname_ext isn't exposed outside fd.c...


Andres Freund

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