Re: Slow alter sequence with PG10.1

On Mon, Jan 22, 2018 at 8:24 AM, Michael Krüger <michael(at)kruegers(dot)email>
wrote:

> Dear community,
>
> I'm using PG10.1 on CentOS Linux release 7.4.1708 (Core) after upgrading
> it from PG9.6.6. My application heavily uses sequences and requires
> different increments of sequence numbers, e.g. a range of 100, 1000 or 5000
> numbers, so it is not possible to set a fixed increment on a sequence that
> can be used by my application.
>
> With PG10.1 the performance has dropped seriously so that my application
> becomes unusable. After investigating different aspects, I was able to
> isolate the issue to be related to the sequences in Postgres 10.1.
>
> Below shows a simple test script showing the problem:
>
> ​[...]​

>
> On my computer I tried this code on PG9.6.6 and it executed in roughly 3
> seconds.
> When running it on PG10.1 it takes over 7 minutes.
>
> Further investigation showed that the problem is related to ALTER
> SEQUENCE...
>
> I can't believe that PG10.1 was changed that dramatically without
> providing a workaround or a way to switch to the old PG9.6 performance, at
> least I can't find anything in the documentation.
>
> Is this a bug?
>

​Without testing/confirming I'd be inclined to agree that this is a
regression for an unusual usage of sequences. Work was done to make
typical use cases of sequences more feature-full and it is quite possible
the added effort involved hurts your specific scenario. I'd expect a
hacker to eventually pick this up, confirm the observation, and provide
feedback. This seems like sufficient amount of detail to get the ball
rolling.

David J.