Horton

Re: Reduce TupleHashEntryData struct size by half

David Rowley <dgrowleyml@gmail.com>

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From: David Rowley <dgrowleyml@gmail.com>
To: Jeff Davis <pgsql@j-davis.com>
Cc: Heikki Linnakangas <hlinnaka@iki.fi>, pgsql-hackers@postgresql.org
Date: 2025-01-14T09:01:57Z
Lists: pgsql-hackers 
On Tue, 14 Jan 2025 at 11:11, Jeff Davis <pgsql@j-davis.com> wrote:
>
> On Sun, 2025-01-12 at 14:54 +1300, David Rowley wrote:
> > I wonder if there's some other better way of doing this. Would it be
> > worth having some function like ExecCopySlotMinimalTuple() that
> > accepts an additional parameter so that the palloc allocates N more
> > bytes at the end?  Maybe it's worth hunting around to see if there's
> > any other executor nodes that could benefit from that infrastructure.
>
> That would be convenient, but doesn't seem like a great separation of
> responsibilities. Perhaps some API that separated the length
> calculation, and accepted a caller-supplied buffer?

The trick would be to ensure ExecClearTuple() still works. You
obviously don't want to try and pfree() something that isn't a pointer
to a palloc'd chunk. I'm not sure what the best API is, but I do see
there are other places that might benefit from something that allows
this.  The two usages of ExecCopySlotMinimalTuple() in nodeMemoize.c
are candidates.

David

Commits

  1. Comment fixups from 626df47ad9.

  2. Remove 'additional' pointer from TupleHashEntryData.

  3. Add ExecCopySlotMinimalTupleExtra().

  4. Create accessor functions for TupleHashEntry.

  5. TupleHashTable: store additional data along with tuple.

  6. ExecInitAgg: update aggstate->numaggs and ->numtrans earlier.

  7. nodeSetOp.c: missing additionalsize for BuildTupleHashTable().

  8. Remove unused TupleHashTableData->entrysize.

  9. Add missing typedefs.list entry for AggStatePerGroupData.