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.

Sherry Moore, Solaris Kernel Development        http://blogs.sun.com/sherrym

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