On 11 October 2012 19:41, Tom Lane <t...@sss.pgh.pa.us> wrote: > Simon Riggs <si...@2ndquadrant.com> writes: >> On 11 October 2012 18:22, Tom Lane <t...@sss.pgh.pa.us> wrote: >>> If it worked, I might be amenable to that, but it doesn't. You can't >>> trigger taking a new snapshot off whether we waited for a lock; that >>> still has race conditions, just ones that are not so trivial to >>> demonstrate manually. (The other transaction might have committed >>> microseconds before you reach the point of waiting for the lock.) > >> So where's the race? > > Same example as before, except that the exclusive-lock-holding > transaction commits (and releases its lock) between the time that the > other transaction takes its parse/plan snapshot and the time that it > takes AccessShare lock on the table.
A cache invalidation could also set the need-second-snapshot flag. -- Simon Riggs http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
