Folks, I'm hoping that some of you can shed some light on this.
I've been trying to peg the "sweet spot" for shared memory using OSDL's equipment. With Jan's new ARC patch, I was expecting that the desired amount of shared_buffers to be greatly increased. This has not turned out to be the case. The first test series was using OSDL's DBT2 (OLTP) test, with 150 "warehouses". All tests were run on a 4-way Pentium III 700mhz 3.8GB RAM system hooked up to a rather high-end storage device (14 spindles). Tests were on PostgreSQL 8.0b3, Linux 2.6.7. Here's a top-level summary: shared_buffers % RAM NOTPM20* 1000 0.2% 1287 23000 5% 1507 46000 10% 1481 69000 15% 1382 92000 20% 1375 115000 25% 1380 138000 30% 1344 * = New Order Transactions Per Minute, last 20 Minutes Higher is better. The maximum possible is 1800. As you can see, the "sweet spot" appears to be between 5% and 10% of RAM, which is if anything *lower* than recommendations for 7.4! This result is so surprising that I want people to take a look at it and tell me if there's something wrong with the tests or some bottlenecking factor that I've not seen. in order above: http://khack.osdl.org/stp/297959/ http://khack.osdl.org/stp/297960/ http://khack.osdl.org/stp/297961/ http://khack.osdl.org/stp/297962/ http://khack.osdl.org/stp/297963/ http://khack.osdl.org/stp/297964/ http://khack.osdl.org/stp/297965/ Please note that many of the Graphs in these reports are broken. For one thing, some aren't recorded (flat lines) and the CPU usage graph has mislabeled lines. -- --Josh Josh Berkus Aglio Database Solutions San Francisco ---------------------------(end of broadcast)--------------------------- TIP 8: explain analyze is your friend