Re: BUG #19040: Memory leak in hashed subplan node due to missing hashtempcxt reset

> On Sep 7, 2025, at 16:24, 李海洋(陌痕) <mohen(dot)lhy(at)alibaba-inc(dot)com> wrote:
>
> On 2025-09-06 20:31:53 Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:
>
> > After contemplating things for awhile, I think that feichanghong’s
> > idea is the right one after all: in each of the functions that switch
> > into hashtable->tempcxt, let's do a reset on the way out, as attached.
> > That's straightforward and visibly related to the required data
> > lifespan.
>
> I have considered this approach as well, but my concern is that "tempcxt"
> is not always an independent memory context. In some cases, it references
> another context — for example, in nodeSetOp.c’s "build_hash_table", “tempcxt"
> points to "setopstate->ps.ps_ExprContext->ecxt_per_tuple_memory". There is
> similar usage in nodeAgg.c as well. I’m not entirely sure that this approach would
> not discard data we still need, because the lifespan of
> "ps_ExprContext->ecxt_per_tuple_memory" seems to be longer than “tempcxt”.

Yes, I agree with that.

> Should we make tempcxt a completely independent memory context?

It looks fine. Perhaps we don't need to pass tempcxt to BuildTupleHashTable,
but rather create a new one within it. After each switch to tempcxt, we should
clean it up using MemoryContextReset.

Best Regards,
Fei Changhong