Re: Adding REPACK [concurrently]

Antonin Houska <ah@cybertec.at>

From: Antonin Houska <ah@cybertec.at>

To: Mihail Nikalayeu <mihailnikalayeu@gmail.com>

Cc: Alvaro Herrera <alvherre@alvh.no-ip.org>, Fujii Masao <masao.fujii@gmail.com>, Robert Treat <rob@xzilla.net>, Pg Hackers <pgsql-hackers@lists.postgresql.org>

Date: 2025-08-26T08:46:00Z

Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

Improve REPACK (CONCURRENTLY) error messages some more
- 378dffaf8c80 19 (unreleased) landed
Add CONCURRENTLY option to REPACK
- 28d534e2ae0a 19 (unreleased) landed
Make index_concurrently_create_copy more general
- 33bf7318f94c 19 (unreleased) landed
Document the 'command' column of pg_stat_progress_repack
- a630ac5c2016 19 (unreleased) landed
Introduce the REPACK command
- ac58465e0618 19 (unreleased) landed
Split vacuumdb to create vacuuming.c/h
- c4067383cb2c 19 (unreleased) landed
Revert changes to CONCURRENTLY that "sped up" Xmin advance
- 042b584c7f7d 14.4 cited

Mihail Nikalayeu <mihailnikalayeu@gmail.com> wrote:

> Antonin Houska <ah@cybertec.at>:
> > I think the problem is that HeapTupleSatisfiesSelf() uses
> > TransactionIdIsInProgress() instead of checking the snapshot:
> 
> Yes, some issues might be possible for SnapshotSelf.
> Possible solution is to override TransactionIdIsCurrentTransactionId
> to true (like you did with nParallelCurrentXids but just return true).
> IIUC, in that case all checks are going to behave the same way as in v5 version.

I assume you mean v12-0005. Yes, that modifies
TransactionIdIsCurrentTransactionId(), so that the the transaction being
replayed recognizes if it (or its subtransaction) performed particular change
itself.

Although it could work, I think it'd be confusing to consider the transactions
being replayed as "current" from the point of view of the backend that
executes REPACK CONCURRENTLY.

But the primary issue is that in v12-0005,
TransactionIdIsCurrentTransactionId() gets the information on "current
transactions" from snapshots - see the calls of SetRepackCurrentXids() before
each scan. It's probably not what you want.

-- 
Antonin Houska
Web: https://www.cybertec-postgresql.com