Hi, I'm running version 8.1 on a dedicated Sun v20 server (2 AMD x64's) with 4Gb of RAM. I have recently noticed that the performance of some more complex queries is extremely variable and irregular. For example, I currently have a query that returns a small number of rows (5) by joining a dozen of tables. Below are the running times obtained by repeatedly lauching this query in psql (nothing else was running on the server at that time): Time: 424.848 ms Time: 1615.143 ms Time: 15036.475 ms Time: 83471.683 ms Time: 163.224 ms Time: 2454.939 ms Time: 188.093 ms Time: 158.071 ms Time: 192.431 ms Time: 195.076 ms Time: 635.739 ms Time: 164549.902 ms As you can see, the performance is most of the time pretty good (less than 1 second), but every fourth of fifth time I launch the query the server seems to go into orbit. For the longer running times, I can see from 'top' that the server process uses almost 100% of a CPU. This is rather worrisome, as I cannot be confident of the overall performance of my application with so much variance in query response times. I suspect a configuration problem related to the cache mechanism (shared_buffers? effective_cache_size?), but to be honest I do not know where to start to diagnose it. I also noticed that the query plan can vary when the same query is launched two times in a row (with no other changes to the DB in between). Is there a random aspect to the query optimizer that could explain some of the observed variance in performance ? Any help would be greatly appreciated. Thanks in advance, J-P
