Re: Sequences - jumped after power failure

Cheers Tom.
I'll note that down under the section '...things to note should the
server crash...' - just under the note that says '...get a UPS...'

On Tue, 2008-04-15 at 10:58 -0400, Tom Lane wrote:

> Steve T <steve(at)retsol(dot)co(dot)uk> writes:
> > I have a set of claims tables that cover the claim itself, the customer,
> > contact points etc. Yesterday there was a power failure and the server
> > suffered an immediate power outage. When the server came back,
> > everything seemed fine, apart from the fact that the claim related
> > sequences had all jumped and left a gap of 33 (last was 52 before power
> > failure, next one allocated after power failure 85). This seems
> > consistent across all the tables related to the claim (it may be across
> > the tables in the database - I haven't checked all of them as yet).
>
> > Does this sound feasible and if so, what is the cause?
>
> Yeah, this is intentional behavior designed to reduce the amount of disk
> write traffic generated by nextval()s. From a standing start, a
> nextval() actually advances the sequence 33 times (1 + SEQ_LOG_VALS),
> so that the next 32 nextval()s won't need to generate their own WAL
> records. I guess you must have crashed before that first nextval()
> was able to commit its result into the database ...
>
> regards, tom lane

Steve Tucknott
ReTSol Ltd

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