On Sat, Sep 26, 2020 at 1:51 PM Julien Rouhaud <rjuju123@gmail.com> wrote:
On Sat, Sep 26, 2020 at 8:17 AM Andy Fan <zhihui.fan1213@gmail.com> wrote: > > As for the testing with cache considered, I found how to estimate cache hit > ratio is hard or how to control a hit ratio to test is hard. Recently I am thinking > a method that we can get a page_reads, shared_buffer_hit from pg_kernel > and the real io (without the file system cache hit) at os level (just as what > iotop/pidstat do). then we can know the shared_buffer hit ratio and file system > cache hit ratio (assume it will be stable after a long run). and then do a testing. > However this would be another branch of manual work and I still have not got > it done until now.
FWIW pg_stat_kcache [1] extension accumulates per (database, user, queryid) physical reads and writes, so you can easily compute a shared_buffers / IO cache / disk hit ratio.
