Re: bgwriter changes

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