| From: | Julien Rouhaud <rjuju123(at)gmail(dot)com> |
|---|---|
| To: | Andy Fan <zhihui(dot)fan1213(at)gmail(dot)com> |
| Cc: | Ashutosh Bapat <ashutosh(dot)bapat(dot)oss(at)gmail(dot)com>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: Dynamic gathering the values for seq_page_cost/xxx_cost |
| Date: | 2020-09-26 05:51:37 |
| Message-ID: | CAOBaU_YWB-j9e0Y=dLpPJhxMTM44yZgN3TJ_VZE1U5n3JAsSMw@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Sat, Sep 26, 2020 at 8:17 AM Andy Fan <zhihui(dot)fan1213(at)gmail(dot)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.
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