On Sat, Feb 20, 2016 at 5:08 AM, Fabien COELHO <coe...@cri.ensmp.fr> wrote:
>> Kernel 3.2 is extremely bad for Postgresql, as the vm seems to amplify IO
>> somehow. The difference to 3.13 (the latest LTS kernel for 12.04) is huge.
>> https://medium.com/postgresql-talk/benchmarking-postgresql-with-different-linux-kernel-versions-on-ubuntu-lts-e61d57b70dd4#.6dx44vipu
> Interesting! To summarize it, 25% performance degradation from best kernel
> (2.6.32) to worst (3.2.0), that is indeed significant.

As far as I recall, the OS cache eviction is very aggressive in 3.2,
so it would be possible that data from the FS cache that was just read
could be evicted even if it was not used yet. Thie represents a large
difference when the database does not fit in RAM.

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