On Thu, Nov 30, 2023 at 12:51:38PM +0100, Tomas Vondra wrote:
> As for implementation/replication, I haven't checked the code, but I'd
> imagine the AM should be able to decide whether something needs to be
> replicated (and how) or not. So the traditional sequences would
> replicate, and the alternative sequences would not replicate anything.
Yep, exactly. Keeping compatibility for the in-core sequence
computation is very important (including the fact that this stuff uses
pseudo-heap tables for its metadata with the values computed).
>> This was the key point that I wanted to discuss or hear opinions
>> about. So, if we wish to have some sort of global sequences then it is
>> not clear to me what benefits will we get by having replication of
>> non-global sequences. One thing that comes to mind is replication
>> covers a subset of use cases (like help in case of failover or
>> switchover to subscriber) and till the time we have some
>> implementation of global sequences, it can help users.
>
> What are you going to do about use cases like using logical replication
> for upgrade to the next major version? Or applications that prefer (or
> have to) use traditional sequences?
Yeah, and that's why the logical replication of sequence has value.
Giving the possibility for users or application developers to use a
custom computation method may be useful for some applications, but not
others. The use cases are too much different, so IMO both are useful,
when applied to each user's requirements.
--
Michael