Heikki Linnakangas wrote:
In any case, I'd like to see more test results before we make a decision. I'm running tests with DBT-2 and a seq scan running in the background to see if the cache-spoiling effect shows up. I'm also trying to get hold of some bigger hardware to run on. Running these tests takes some calendar time, but the hard work has already been done. I'm going to start reviewing Jeff's synchronized scans patch now.

Here are the results of the DBT-2 tests:


In each of these tests, at the end of rampup a script is started that issues a "SELECT COUNT(*) FROM stock" in a loop, with 2 minute delay between end of previous query and start of next one.

The patch makes the seq scans go significantly faster. In the 1 hour test period, the patched tests perform roughly 30-100% as many selects as unpatched tests.

With 100 and 105 warehouses, it also significantly reduces the impact of the seq scan on other queries; response times are lower with the patch. With 120 warehouses the reduction of impact is not as clear, but when you plot the response times it's still there (the plots on the "response times charts"-page are useless because they're overwhelmed by the checkpoint spike).

  Heikki Linnakangas
  EnterpriseDB   http://www.enterprisedb.com

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