Robert Haas <robertmh...@gmail.com> writes: > On Thu, Jul 28, 2011 at 10:17 AM, Hannu Krosing <ha...@2ndquadrant.com> wrote: >> My hope was, that this contention would be the same than simply writing >> the WAL buffers currently, and thus largely hidden by the current WAL >> writing sync mechanisma. >> >> It really covers just the part which writes commit records to WAL, as >> non-commit WAL records dont participate in snapshot updates.
> I'm confused by this, because I don't think any of this can be done > when we insert the commit record into the WAL stream. It has to be > done later, at the time we currently remove ourselves from the > ProcArray. Those things need not happen in the same order, as I noted > in my original post. But should we rethink that? Your point that hot standby transactions on a slave could see snapshots that were impossible on the parent was disturbing. Should we look for a way to tie "transaction becomes visible" to its creation of a commit WAL record? I think the fact that they are not an indivisible operation is an implementation artifact, and not a particularly nice one. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers