Hi Simon, > and what you haven't said > > - all of this is orthogonal to the issue of buffer cache spoiling in > PostgreSQL itself. That issue does still exist as a non-OS issue, but > we've been discussing in detail the specific case of L2 cache effects > with specific kernel calls. All of the test results have been > stand-alone, so we've not done any measurements in that area. I say this > because you make the point that reducing the working set size of write > workloads has no effect on the L2 cache issue, but ISTM its still > potentially a cache spoiling issue.
What I wanted to point out was that (reiterating to avoid requoting), - My test was simply to demonstrate that the observed performance difference with VACUUM was caused by whether the size of the user buffer caused L2 thrashing. - In general, application should reduce the size of the working set to reduce the penalty of TLB misses and cache misses. - If the application access pattern meets the NTA trigger condition, the benefit of reducing the working set size will be much smaller. Whatever I said is probably orthogonal to the buffer cache issue you guys have been discussing, but I haven't read all the email exchange on the subject. Thanks, Sherry -- Sherry Moore, Solaris Kernel Development http://blogs.sun.com/sherrym ---------------------------(end of broadcast)--------------------------- TIP 9: In versions below 8.0, the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match