From: Tom Lane <tgl@sss.pgh.pa.us>
To: Jeff Davis <pgsql@j-davis.com>
cc: Scott Carey <scott.carey@algonomy.com>,
        David Rowley <dgrowleyml@gmail.com>,
        pgsql-performance@lists.postgresql.org
Subject: Re: Significant performance issues with array_agg() + HashAggregate
 plans on Postgres 17
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Comments: In-reply-to Jeff Davis <pgsql@j-davis.com>
	message dated "Fri, 03 Apr 2026 12:36:23 -0700"
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Date: Fri, 03 Apr 2026 15:56:22 -0400
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Jeff Davis <pgsql@j-davis.com> writes:
> One idea would be to update parent contexts' memory totals recursively
> each time a subcontext allocates a new block. Block allocations are
> infrequent enough that may be acceptable.

> If we are worried about affecting unrelated cases, we could set an
> "accounting_enabled" flag for the contexts we care about, which would
> be automatically inherited by subcontexts, and then stop recursing up
> when that flag is false.

Yeah, I was speculating about similar ideas.  Since mem_allocated
is only changed after a malloc() or free() call, it probably
wouldn't add too much overhead to propagate that up to parent
contexts.  I agree with having a flag to prevent the propagation
from going up further than we actually care about, though.

Would it make sense to accumulate those values in a separate field
child_mem_allocated, rather than redefining what mem_allocated
means?

			regards, tom lane