Simon Riggs wrote: > On 28 December 2012 10:21, Simon Riggs <si...@2ndquadrant.com> wrote: > > > * There is a fixed 75% heuristic in the patch. > > I'm concerned that we're doing extra work while holding the buffer > locked, which will exacerbate any block contention that exists. > > We have a list of the columns that the UPDATE is touching since we use > that to check column permissions for the UPDATE. Which means we should > be able to use that list to check only the columns actually changing > in this UPDATE statement.
But that doesn't include columns changed by triggers, AFAIR, so you could only use that if there weren't any triggers. I was also worried about the high variance in the results. Those averages look rather meaningless. Which would be okay, I think, because it'd mean that performance-wise the patch is a wash, but it is still achieving a lower WAL volume, which is good. -- Álvaro Herrera 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
