Re: Adding REPACK [concurrently]

On 2026-Mar-25, Antonin Houska wrote:

> I've taken a look, but not sure if the tuple slots help here. In
> heapam_relation_copy_for_cluster(), both table_scan_getnextslot() and
> index_getnext_slot() call ExecStoreBufferHeapTuple() ->
> tts_buffer_heap_store_tuple(), which AFAICS do not deform the tuple.
> Then ExecFetchSlotHeapTuple() is used to retrieve the tuple, but
> again, the underlying slot (TTSOpsBufferHeapTuple) handles it by
> copying rather than deforming / forming. Thus I think the explicit
> "reforming" currently does not add any performance overhead.

Looking again, I think we should leave this alone for now.  The existing
code (looking at heapam_relation_copy_for_cluster) is somewhat silly, in
that we do a bunch of operations with slots, then we heap-ify the tuple
by doing ExecFetchSlotHeapTuple(), then we do the reform_and_rewrite
dance, which must deform the tuple only to immediately form it back; and
after we've done that, we make it go through the rewriteheap.c motions,
which again deforms and forms back (in certain cases).

This code structure seems mostly a relic from the time when heapam.c was
all we had, and I think we should rewrite it from scratch to work using
only slots.  But not for this patch, and not for pg19, because I think
that's going to take some nontrivial effort on its own.  So for REPACK
in pg19 I think we should just do the simplest thing possible, and do
the minimum amount of deform/form dance necessary to make this whole
thing work.  I suppose that that's what the submitted code (v44-0008)
does, so I'm going to leave it at that.

-- 
Álvaro Herrera               48°01'N 7°57'E  —  https://www.EnterpriseDB.com/
"In Europe they call me Niklaus Wirth; in the US they call me Nickel's worth.
 That's because in Europe they call me by name, and in the US by value!"