Horton

Re: pg11+: pg_ls_*dir LIMIT 1: temporary files .. not closed at end-of-transaction

Justin Pryzby <pryzby@telsasoft.com>

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From: Justin Pryzby <pryzby@telsasoft.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-hackers@postgresql.org, Fabien COELHO <coelho@cri.ensmp.fr>, Alvaro Herrera <alvherre@2ndquadrant.com>, David Steele <david@pgmasters.net>, "Bossart, Nathan" <bossartn@amazon.com>, Thomas Munro <thomas.munro@gmail.com>
Date: 2020-03-08T19:14:56Z
Lists: pgsql-hackers 
On Sun, Mar 08, 2020 at 02:37:49PM -0400, Tom Lane wrote:
> Justin Pryzby <pryzby@telsasoft.com> writes:
> > While working on a patch, I noticed this pre-existing behavior, which seems to
> > be new since v11, maybe due to changes to SRF.
> 
> > |postgres=# SELECT pg_ls_dir('.') LIMIT 1;
> > |WARNING:  1 temporary files and directories not closed at end-of-transaction
> 
> Hmm, actually it looks to me like pg_ls_dir has been broken forever.
> The reason the warning didn't show up before v11 is that CleanupTempFiles
> didn't bleat about leaked "allocated" directories before that
> (cf 9cb7db3f0).
> 
> I guess we ought to change that function to use returns-a-tuplestore
> protocol instead of thinking it can hold a directory open across calls.
> It's not hard to think of use-cases where the existing behavior would
> cause issues worse than a nanny-ish WARNING, especially on platforms
> with tight "ulimit -n" limits.

Thanks for the analysis.

Do you mean it should enumerate all files during the initial SRF call, or use
something other than the SRF_* macros ?

-- 
Justin

Commits

  1. Teach pg_ls_dir_files() to ignore ENOENT failures from stat().

  2. Remove useless pfree()s at the ends of various ValuePerCall SRFs.

  3. Avoid holding a directory FD open across assorted SRF calls.

  4. Document pg_ls_*dir hiding of directories and special files

  5. Avoid holding a directory FD open across pg_ls_dir_files() calls.

  6. Adjust nodeFunctionscan.c to reset transient memory context between calls