Re: How to find if a SELECT is reading from buffer or disk ?

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Balkrishna Sharma <b_ki@xxxxxxxxxxx> wrote:
 
> I am increasing the shared_buffer size in postgresql.conf and want
> to measure its effect on READ. In essence I want to know if the
> SELECT queries I am firing repeatedly is reading from the buffer
> or going directly to the disk.
 
There's a third option -- PostgreSQL reads and writes will normally
go through the OS cache.
 
> Right now I am just looking at execution time of the SELECTs and
> trying to conclude. But there should be a direct way to see where
> the SELECT reads from.
> How can I accomplish this ?
 
You didn't mention your OS.  There's usually a way to monitor disk
I/O built in to the OS.  I usually start with:
 
vmstat 1
 
-Kevin

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