Re: Adding REPACK [concurrently]

Mihail Nikalayeu <mihailnikalayeu@gmail.com> wrote:

> Antonin Houska <ah@cybertec.at>:
>
> > 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.
>
> Just realized SnapshotDirty is the thing that fits into the role - it
> respects not-yet committed transactions, giving enough information to
> wait for them.
> It is already used in a similar pattern in
> check_exclusion_or_unique_constraint and RelationFindReplTupleByIndex.
>
> So, it is easy to detect the case of the race you described previously
> and retry + there is no sense to hack around
> TransactionIdIsCurrentTransactionId.

Where exactly should HeapTupleSatisfiesDirty() conclude that the tuple is
visible? TransactionIdIsCurrentTransactionId() will not do w/o the
modifications that you proposed earlier [1] and TransactionIdIsInProgress() is
not suitable as I explained in [2].

I understand your idea that there are no transaction aborts in the new table,
which makes things simpler. I cannot judge if it's worth inventing a new kind
of snapshot. Anyway, I think you'd then also need to hack
HeapTupleSatisfiesUpdate(). Isn't that too invasive?

[1] https://www.postgresql.org/message-id/CADzfLwUqyOmpkLmciecBy4aBN1sohQVZ2Hgc6m-tjSUqDRHwyQ%40mail.gmail.com
[2] https://www.postgresql.org/message-id/24483.1756142534%40localhost

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