On 2013-05-22 23:05:40 -0400, Robert Haas wrote: > On Wed, May 22, 2013 at 11:02 PM, Andres Freund <and...@2ndquadrant.com> > wrote: > > On 2013-05-22 22:51:13 -0400, Robert Haas wrote: > >> In discussions today, Tom Lane suggested testing the time to start up > >> a backend and run a simple query such as "SELECT 2+2" in the absence > >> of a relcache file. > > > >> I did this and can't measure any overhead as a result of MVCC catalog > >> access. I tried it with no active connections. I tried it with 600 > >> idle active connections (to make taking MVCC snapshots more > >> expensive). > > > > Did you try it with the 600 transactions actually being in a transaction > > and having acquired a snapshot? > > No... I can hack something up for that.
Make that actually having acquired an xid. We skip a large part of the work if a transaction doesn't yet have one afair. I don't think the mere presence of 600 idle connections without an xid in contrast to just having max_connection at 600 should actually make a difference in the cost of acquiring a snapshot? Greetings, Andres Freund -- Andres Freund 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
