Re: logical replication: could not create file "state.tmp": File exists

On 12/2/19 7:35 AM, Michael Paquier wrote:
> On Sat, Nov 30, 2019 at 03:09:39PM +0300, Grigory Smolkin wrote:
>> I`ve digged a bit into this problem, and it`s turned out that in
>> SaveSlotToPath() temp file for replication slot is opened with 'O_CREAT |
>> O_EXCL' flags, which makes this routine as not very reentrant.
> What did you see as I/O problem before facing the actual error
> reported here? Was it just ENOSPC, a fsync failure, or just a failure
> in closing the fd? The first pattern is mostly what I guess happened,
> still a fsync failure would not trigger a PANIC here (actually we
> really should do that!), but I am raising a different thread about
> that issue.

Hello!

I didn`t see the very first error that left behind the temp file.
I`ve requested it just now, but it will take some time to get it (there
are several terabytes of text log).
But I assume that it was out of space error, which, by the look of the
code, should produce ERROR and leave temp file behind, just as it
happened in aforementioned  case.

>
>> Since an exclusive lock is taken before temp file creation, I think it
>> should be safe to replace O_EXCL with O_TRUNC.
>> Script to reproduce and patch are attached.
> Agreed. I prefer the O_TRUNC option because that's less code churn.
> Also, as it can still be useful to have a look at the temporary state
> file after a crash or a failure, doing unlink() in the error code
> paths is no good option IMO.

I`m sorry, but it was an production system, so, as I understand it,
stale temp file was hastily deleted without long considerations.

Thank you for your interest in this topic.

>
> Have others thoughts or objections to share?
> --
> Michael

--
Grigory Smolkin
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