RE: Adding REPACK [concurrently]

On Thursday, May 28, 2026 11:34 AM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> On Wed, May 27, 2026 at 5:31 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
> wrote:
> >
> > On Wed, May 27, 2026 at 1:08 AM Zhijie Hou (Fujitsu)
> > <houzj(dot)fnst(at)fujitsu(dot)com> wrote:
> > >
> > > 0001 remains unchanged.
> > >
> >
> > Few minor comments:
> > =================
>
> Commit message says: "This change does not advance catalog_xmin.
> REPACK already holds a snapshot that prevents catalog dead tuple removal,
> so catalog_xmin handling can be addressed independently.".
> Isn't it equally important to advance this, otherwise, for long running REPACKs
> dead tuples will be accumulated needlessly? If so, do we have any ideas to
> avoid this?

My understanding is that dead tuple accumulation is common to all long-running
commands (including CLUSTER, VACUUM FULL, and REPACK without CONCURRENTLY). As
long as a command holds a snapshot for a long time while scanning and copying
data, the backend xmin will cause similar accumulation. So, this doesn't seem
like a new issue to me, and given that catalog_xmin only affect tuples in system
catalog which is less harmful, I thought it could be handled independently.
There was a proposal to improve this case in [1]. Sorry if I've missed something.

Attaching the v4 patch which improved the comments and commit message as
suggested.

[1] https://www.postgresql.org/message-id/125085.1775827305%40localhost

Best Regards,
Hou zj