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From: Mihail Nikalayeu <mihailnikalayeu@gmail.com>
Date: Wed, 27 Aug 2025 12:55:12 +0200
Message-ID: 
 <CADzfLwXCTXNdxK-XGTKmObvT=_QnaCviwgrcGtG9chsj5sYzrg@mail.gmail.com>
Subject: Re: Adding REPACK [concurrently]
To: Antonin Houska <ah@cybertec.at>
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>
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Antonin Houska <ah@cybertec.at>:

> Do you mean the race related to TransactionIdIsInProgress()? Not sure I
> understand, as you suggested above that you no longer need the function.

The "lightweight" approaches I see so far:
* XactLockTableWait before replay + SnapshotSelf(GetLatestSnapshot?)
* SnapshotDirty + retry logic
* SnapshotBelieveEverythingCommitted + modification of
HeapTupleSatisfiesUpdate (because it called by heap_update and looks
into TransactionIdIsInProgress)

> It does not really worry me. The pg_squeeze extension is not MVCC-safe and I
> remember there were only 1 or 2 related complaints throughout its
> existence. (pg_repack isn't MVCC-safe as well, but I don't keep track of its
> issues.)

But pg_squeeze and pg_repack are extensions. If we are moving that
mechanics into core I'd expect some improvements over pg_squeeze.
MVCC-safety of REINDEX CONCURRENTLY makes it possible to run it on a
regular basis as some kind of background job. It would be nice to have
something like this for the heap.

I agree the initial approach is too invasive, complex and
performance-heavy to push it forward now.
But, any of "lightweight" feels like a good candidate to be shipped
with the feature itself - relatively easy and non-invasive.

Best regards,
Mikhail.