On Sun, Aug 21, 2016 at 11:13 PM, Craig Ringer <craig@2ndquadrant.com> wrote:
> If the sequence is created in the current xact (i.e. uncommitted) we have to
> add the sequence updates to that xact to be replayed only if it commits. The
> sequence is visible only to the toplevel xact that created the sequence so
> advances of it can only come from that xact and its children. The actual
> CREATE SEQUENCE is presumed to be handled separately by an event trigger or
> similar.
>
> If the new sequence is committed we must replay sequence advances
> immediately and non-transactionally to ensure they're not lost due to xact
> rollback or replayed in the wrong order due to xact commit order.
So, I wish I could give you some better advice on this topic, but
sadly I am not an expert in this area. However, it seems to me that
this is just one facet of a much more general problem: given two
transactions T1 and T2, the order of replay must match the order of
commit unless you can prove that there are no dependencies between
them. I don't see why it matters whether the operations are sequence
operations or data operations; it's just a question of whether they're
modifying the same "stuff".
Of course, it's possible I'm missing something important here...
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company