Jeff Janes wrote:
In my test cases, the syncs that the backends were doing were almost always to the same file that the checkpoint writer was already choking on (so they are entangled simply by virtue of that). So very quickly all the backends hit the same wall and thunked to a halt. This is probably a feature of trying to use pgbench as the basis to get a very artificial model.
Yes--pgbench has some problems like you describe, ones that are a bit different than the way I've seen fsync writes get in each other's way in the production systems I've looked at. That's good if you really want to provoke this behavior, which is one reason why I've used as an example for my patches so far (the other being that it's already available in everyone's installation). But it's tough to get it to act more like a real-world system, which don't have quite so many localized updates, without cranking the scale way up. And that then tends to aggravate other problems too.
The 8.3 checkpoint spreading work also got some useful results using the dbt-2 benchmark. I'm at the point where I think I need to return to that test program for what I'm doing now. I'd encourage you to try that out too if you get a chance.
Thanks for the feedback and the review. I hope you appreciate now why I suggested you wait for the stuff I was submitting before getting back into the sorted checkpoint topic again. That should be a lot easier to make sense of with this instrumentation in place.
-- Greg Smith 2ndQuadrant US g...@2ndquadrant.com Baltimore, MD PostgreSQL Training, Services and Support www.2ndQuadrant.us "PostgreSQL 9.0 High Performance": http://www.2ndQuadrant.com/books -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
