On Tue, Oct 26, 2010 at 8:10 AM, Simon Riggs <si...@2ndquadrant.com> wrote: > I agree with your analysis. Let me review... > [review]
Sounds like we're on the same page. > Two options for resolution are > > 1) Throw SERIALIZABLE error > > 2) Implement something similar to EvalPlanQual > As you say, we already resolve this situation for concurrent updates by > following the update chain from a row that is visible to the latest row. > For MERGE the semantics need to be subtely different here: we need to > follow the update chain to the latest row, but from a row that we > *can't* see. > > MERGE is still very useful without the need for 2), though fails in some > cases for concurrent use. The failure rate would increase as the number > of concurrent MERGErs and/or number of rows in source table. Those > errors are no more serious than are possible now. > > So IMHO we should implement 1) now and come back later to implement 2). > Given right now there may be other issues with 2) it seems unsafe to > rely on the assumption that we'll fix them by end of release. Yeah. In fact, I'm not sure we're ever going to want to implement #2 - I think that needs more study to determine whether there's even something there that makes sense to implement at all. But certainly I wouldn't count on it happening for 9.1. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
