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: 2020-03-12T12:12:06Z
Lists: pgsql-hackers 
On Sun, Mar 08, 2020 at 04:30:44PM -0400, Tom Lane wrote:
> BTW, another thing I noticed while looking around is that some of
> the functions using SRF_RETURN_DONE() think they should clean up
> memory beforehand.  This is a waste of code/cycles, as long as the
> memory was properly allocated in funcctx->multi_call_memory_ctx,
> because funcapi.c takes care of deleting that context.
> 
> We should probably document that *any* manual cleanup before
> SRF_RETURN_DONE() is an antipattern.  If you have to have cleanup,
> it needs to be done via RegisterExprContextCallback instead.

This part appears to be already in place since
e4186762ffaa4188e16702e8f4f299ea70988b96:

|The memory context that is current when the SRF is called is a transient
|context that will be cleared between calls. This means that you do not need to
|call pfree on everything you allocated using palloc; it will go away anyway.
|However, if you want to allocate any data structures to live across calls, you
|need to put them somewhere else. The memory context referenced by
|multi_call_memory_ctx is a suitable location for any data that needs to survive
|until the SRF is finished running. In most cases, this means that you should
|switch into multi_call_memory_ctx while doing the first-call setup.

-- 
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