Re: how to know whether query data from memory after pg_prewarm

On Wed, Sep 19, 2018 at 1:35 PM jimmy <mpokky(at)126(dot)com> wrote:
> I use select pg_prewarm('table1','read','main') to load data of table1 into the memory.
> when I use select count(1) from table1 group by aa to query data.
> I find the speed of query is not fast, I wonder whether it query data from memory.
> And it is slower than Oracle, both of Oracle and Postgresql has same table and count of data.
> when pg_prewarm use 'read' mode, the data is put into the OS cache, how to examine the table which is pg_prewarmed into the OS cache .
> I know pg_buffercache ,but it just examine the table in the shared buffer of Postgresql, not the table in the OS cache.

This is a quick and dirty hack, but it might do what you want:

https://github.com/macdice/pgdata_mincore

Tested on FreeBSD, not sure how well it'll travel.

--
Thomas Munro
http://www.enterprisedb.com