On 2/23/23 7:56 AM, Tomas Vondra wrote:
On 2/22/23 18:04, Jonathan S. Katz wrote:On 2/22/23 5:02 AM, Tomas Vondra wrote:
Interestingly, in systems that tend to have higher rates of failover (I'm thinking of a few distributed systems), this may cause int4 sequences to exhaust numbers slightly (marginally?) more quickly. Likely not too big of an issue, but something to keep in mind.IMHO the number of systems that would work fine with int4 sequences but this change results in the sequences being "exhausted" too quickly is indistinguishable from 0. I don't think this is an issue.
I agree it's an edge case. I do think it's a number greater than 0, having seen some incredibly flaky setups, particularly in distributed systems. I would not worry about it, but only mentioned it to try and probe edge cases.
Well, yeah. We don't support active-active logical replication (at least not with the built-in). You can easily get into similar issues without sequences.The "origin=none" feature lets you replicate tables bidirectionally. While it's not full "active-active", this is a starting point and a feature for v16. We'll definitely have users replicating data bidirectionally with this.Well, then the users need to use some other way to generate IDs, not local sequences. Either some sort of distributed/global sequence, UUIDs or something like that.
[snip]
In any case, we should update the restrictions in [2] to state: while sequences can be replicated, there is additional work required if you are bidirectionally replicating tables that use sequences, esp. if used in a PK or a constraint. We can provide alternatives to how a user could set that up, i.e. not replicates the sequences or do something like in [3].I agree. I see this as mostly a documentation issue.
Great. I agree that users need other mechanisms to generate IDs, but we should ensure we document that. If needed, I'm happy to help with the docs here.
Thanks, Jonathan
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