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

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