On Thu, 23 Aug 2007, Dmitry Potapov wrote:
I'm planning to do so, but before I need to take a look at postgresql source and dev documentation to find how exactly IO is done, to be able to explain the issue to linux kernel people.
I can speed that up for you. http://developer.postgresql.org/index.php/Buffer_Cache%2C_Checkpoints%2C_and_the_BGW outlines all the source code involved. Easiest way to browse through the code is it via http://doxygen.postgresql.org/ , eventually I want to update the page so it points right into the appropriate doxygen spots but haven't gotten to that yet.
By the way, does postgresql has a similar stall problem on freebsd/other OS'es? It would be interesting to study their approach to io smoothing if it doesn't.
There's some evidence that something about Linux aggrevates the problem; check out http://archives.postgresql.org/pgsql-hackers/2007-07/msg00261.php and the rest of the messages in that thread. I haven't heard a report of this problem from someone who isn't running Linux, but as it requires a certain level of hardware and a specific type of work load I'm not sure if this is coincidence or a cause/effect relationship.
Is there any other changes in 8.3devel that can affect the results of such test?
The "all" component of the background writer was removed as it proved not to be useful once checkpoint_completion_target was introduced. And the LRU background writer keeps going while checkpoints are being trickled out, in earlier versions that didn't happen.
The test I'd like to see more people run is to simulate their workloads with checkpoint_completion_target set to 0.5, 0.7, and 0.9 and see how each of those settings works relative to the 8.2 behavior.
-- * Greg Smith [EMAIL PROTECTED] http://www.gregsmith.com Baltimore, MD ---------------------------(end of broadcast)--------------------------- TIP 4: Have you searched our list archives? http://archives.postgresql.org
