Re: logical decoding and replication of sequences, take 2

On 7/24/23 14:57, Ashutosh Bapat wrote:
> ...
>
>>
>>
>> 2) Currently, the sequences hash table is in reorderbuffer, i.e. global.
>> I was thinking maybe we should have it in the transaction (because we
>> need to do cleanup at the end). It seem a bit inconvenient, because then
>> we'd need to either search htabs in all subxacts, or transfer the
>> entries to the top-level xact (otoh, we already do that with snapshots),
>> and cleanup on abort.
>>
>> What do you think?
>
> Hash table per transaction seems saner design. Adding it to the top
> level transaction should be fine. The entry will contain an XID
> anyway. If we add it to every subtransaction we will need to search
> hash table in each of the subtransactions when deciding whether a
> sequence change is transactional or not. Top transaction is a
> reasonable trade off.
>

It's not clear to me what design you're proposing, exactly.

If we track it in top-level transactions, then we'd need copy the data
whenever a transaction is assigned as a child, and perhaps also remove
it when there's a subxact abort.

And we'd need to still search the hashes in all toplevel transactions on
every sequence increment - in principle we can't have increment for a
sequence created in another in-progress transaction, but maybe it's just
not assigned yet.

regards

--
Tomas Vondra
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