Hi Simon, In another thread you mentioned you were lacking information from me:
On Tue, May 4, 2010 17:10, Simon Riggs wrote: > > There is no evidence that Erik's strange performance has anything to do > with HS; it hasn't been seen elsewhere and he didn't respond to > questions about the test setup to provide background. The profile didn't > fit any software problem I can see. > I'm sorry if I missed requests for things that where not already mentioned. Let me repeat: OS: Centos 5.4 2 quadcores: Intel(R) Xeon(R) CPU X5482 @ 3.20GHz Areca 1280ML primary and standby db both on a 12 disk array (sata 7200rpm, Seagat Barracuda ES.2) It goes without saying (I hope) that apart from the pgbench tests and a few ssh sessions (myself), the machine was idle. It would be interesting if anyone repeated these simple tests and produced evidence that these non-HS. (Unfortunately, I have at the moment not much time for more testing) thanks, Erik Rijkers On Sun, April 25, 2010 21:07, Simon Riggs wrote: > On Sun, 2010-04-25 at 20:25 +0200, Erik Rijkers wrote: > >> Sorry if it's too much data, but to me at least it was illuminating; >> I now understand the effects of the different parameters better. > > That's great, many thanks. > > A few observations > > * Standby performance is actually slightly above normal running. This is > credible because of the way snapshots are now taken. We don't need to > scan the procarray looking for write transactions, since we know > everything is read only. So we scan just the knownassignedxids, which if > no activity from primary will be zero-length, so snapshots will actually > get taken much faster in this case on standby. The snapshot performance > on standby is O(n) where n is the number of write transactions > "currently" on primary (transfer delays blur the word "currently"). > > * The results for scale factor < 100 are fine, and the results for >100 > with few connections get thrown out by long transaction times. With > larger numbers of connections the wait problems seem to go away. Looks > like Erik (and possibly Hot Standby in general) has an I/O problem, > though "from what" is not yet determined. It could be just hardware, or > might be hardware plus other factors. > > -- > Simon Riggs www.2ndQuadrant.com > > -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
