Mark Kirkwood wrote:
It occurs to me that cranking up the number of transactions (say 1000->100000) and seeing if said regression persists would be interesting. This would give the smoothing effect of the bgwriter (plus the ARC) a better chance to shine.
I ran a few of these over the weekend - since it rained here :-) , and the results are quite interesting:
[2xPIII, 2G, 2xATA RAID 0, FreeBSD 5.3 with the same non default Pg parameters as before]
clients = 4 transactions = 100000 (/client), each test run twice
Version tps 7.4.6 49 8.0.0.0RC1 50 8.0.0.0RC1 + rem 49 8.0.0.0RC1 + bg2 50
Needless to way, all well within measurement error of each other (the variability was about 1).
I suspect that my previous tests had too few transactions to trigger many (or any) checkpoints. With them now occurring in the test, they look to be the most significant factor (contrast with 70-80 tps for 4 clients with 1000 transactions).
Also with a small number of transactions, the fsyn'ed blocks may have all fitted in the ATA disk caches (2x2M). In hindsight I should have disabled this! (might run the smaller no. transactions again with hw.ata.wc=0 and see if this is enlightening)
regards
Mark
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