On Fri, Aug 8, 2014 at 6:01 AM, Heikki Linnakangas <hlinnakan...@vmware.com> wrote: > It's possible that two backends arrive at phase 3 at the same time, with > different values. For example, backend A wants to update the minimum to > contain 10, and and backend B wants to update it to 5. Now, if backend B > gets to update the tuple first, to 5, backend A will update the tuple to 10 > when it gets the lock, which is wrong. > > The simplest solution would be to get the buffer lock in exclusive mode to > begin with, so that you don't need to release it between steps 2 and 5. That > might be a significant hit on concurrency, though, when most of the > insertions don't in fact have to update the value. Another idea is to > re-check the updated values after acquiring the lock in exclusive mode, to > see if they match the previous values.
No, the simplest solution is to re-check the bounds after acquiring the exclusive lock. So instead of doing the addValue with share lock, do a consistency check first, and if it's not consistent, do the addValue with exclusive lock. -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
