On Tue, Jul 10, 2012 at 6:48 PM, Tom Lane
<tgl@sss.pgh.pa.us> wrote:
Andy Chambers <
achambers@mcna.net> writes:
> When testing the failover procedure, we noticed that when the new master
> comes up, some sequences have moved forward (by between 30 and 40). I see
> there's a "cache" option when creating the sequence but we're not using
> that.
> Is this to be expected?
WAL records generated by nextval() calls --- server processes will write
WAL records that say they've consumed multiple sequence values ahead of
where they actually have.
AFAICS this is not distinguishably different from the case where a
transaction consumes that number of sequence values and then rolls back,
so I don't see much wrong with that optimization.
OK Cool. Thanks for confirming.
I think I made a poor decision by having our application generate checkbook numbers on demand using sequences. I've since realized (due to this and other reasons like not being able to see what nextval() would return without actually moving the sequence forward) that it would probably be better to generate an entire checkbook's worth of numbers whenever the checks are physically received from the bank. Then just have the app pull the next available check.
Andy
