On May 24, 2017 6:57:08 AM EDT, Robert Haas <robertmh...@gmail.com> wrote:
>On Tue, May 23, 2017 at 11:25 PM, Andres Freund <and...@anarazel.de>
>> On 2017-05-23 22:47:07 -0400, Robert Haas wrote:
>>> On Mon, May 22, 2017 at 11:42 AM, Andres Freund <and...@anarazel.de>
>>> > Ooops.
>>> >
>>> > Two issues: Firstly, we get a value smaller than seqmin, obviously
>>> > that's not ok. But even if we'd error out, it'd imo still not be
>>> > because we have a command that behaves partially transactionally
>>> > (keeping the seqmax/min transactionally), partially not (keeping
>>> > current sequence state at -9).
>>> I don't really agree that this is broken.
>> Just a quick clarification question: You did notice that nextval() in
>> after the rollback returned -9, despite seqmin being 0?  I can see
>> erroring out being acceptable, but returning flat out wrong
>I did see that.  I'm unclear what you think it should do instead.  I
>mean, it could notice that cur_val < min_val and return min_val, but
>that doesn't have a very good chance of being correct either.  I
>suppose the aborted transaction could try to restore the old cur_val
>when it rolls back, but that's clearly the wrong thing when there's no
>DDL involved (plus I'm not sure it would even be safe to try to do
>that).  Do you have an idea?

At the very least we'll have to error out. That's still not nice usability 
wise, but it sure beats returning flat out wrong values.

I suspect that the proper fix would be to use a different relfilenode after 
ddl, when changing the seq file itself (I.e. setval and restart).  That seems 
like it'd be architecturally more appropriate, but also some work.

Sent from my Android device with K-9 Mail. Please excuse my brevity.

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