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Thread: mdtruncate leaking fd.c handles?

mdtruncate leaking fd.c handles?

From
Andres Freund
Date:
Hi,

Am I missing something or is md.c:mdtruncate() leaking open files?
The relevant piece of code is:
    if (priorblocks > nblocks)    {        /*         * This segment is no longer active (and has already been unlinked
       * from the mdfd_chain). We truncate the file, but do not delete         * it, for reasons explained in the
headercomments.         */        if (FileTruncate(v->mdfd_vfd, 0) < 0)            ereport(ERROR,
(errcode_for_file_access(),                    errmsg("could not truncate file \"%s\": %m",
FilePathName(v->mdfd_vfd))));
        if (!SmgrIsTemp(reln))            register_dirty_segment(reln, forknum, v);        v = v->mdfd_chain;
Assert(ov!= reln->md_fd[forknum]); /* we never drop the 1st                                             * segment */
   pfree(ov);    }
 

note that we're freeing the chain entry, which contains the mdfd_vfd,
without previously calling FileClose().

This only really matters for VACUUM truncate and ON COMMIT TRUNCATE temp
table truncation afaics.  But it seems like we should fix it everywhere
nonetheless.

Greetings,

Andres Freund

Re: mdtruncate leaking fd.c handles?

From
Tom Lane
Date:
Andres Freund <andres@anarazel.de> writes:
> Am I missing something or is md.c:mdtruncate() leaking open files?

Yeah, I think you're right.

> This only really matters for VACUUM truncate and ON COMMIT TRUNCATE temp
> table truncation afaics.

Also, you'd need a table > 1GB to leak anything at all, which probably
helps explain why it hasn't been noticed.
        regards, tom lane

Re: mdtruncate leaking fd.c handles?

From
Andres Freund
Date:
On 2016-09-08 18:39:56 -0400, Tom Lane wrote:
> Andres Freund <andres@anarazel.de> writes:
> > Am I missing something or is md.c:mdtruncate() leaking open files?
> 
> Yeah, I think you're right.
> 
> > This only really matters for VACUUM truncate and ON COMMIT TRUNCATE temp
> > table truncation afaics.
> 
> Also, you'd need a table > 1GB to leak anything at all, which probably
> helps explain why it hasn't been noticed.

Heh, this bug is of some older vintage... Appears to originate in
1a5c450f3024ac57cd6079186c71b3baf39e84eb - before that we did a
FileUnlink(), which includes a FileClose().

Will fix.

Andres

Re: mdtruncate leaking fd.c handles?

From
Andres Freund
Date:
On 2016-09-08 15:50:42 -0700, Andres Freund wrote:
> > Andres Freund <andres@anarazel.de> writes:
> > > Am I missing something or is md.c:mdtruncate() leaking open files?

> Will fix.

And done.