Thread: Flush Shared Buffer Cache

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Suvankar Roy wrote:
>
> Hi,
>
> Can anyone help me out with how to flush out Shared Buffer Cache in
> Postgres.
>
> One way would be to restart the database, but I would like to avoid that.
AFAIK, that's the only way.

Is there a reason that you need to dump the shared buffers?  Perhaps if
we knew what you were trying to accomplish we could provide you with a
suitable solution that doesn't require a restart...

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Chander Ganesan
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Suvankar Roy <suvankar.roy@tcs.com> wrote:

> Actually I am trying to figure out how much execution time any query
> is taking is taking when executed for the first time.
>
> Because once a query is executed for the first time, the query plan,
> data buffer is cached so subsequently time taken is much lower.
>
> For this, I want to have the Shared buffer cache flushed to note
> the initial execution time.
>
> Is my understanding correct here ?

Keep in mind that the OS cache will also normally have a significant
amount of PostgreSQL data cached.  For "uncached" timings, you will
need to purge this, too.  Of course, for real-life production
benchmarks the most meaningful timings are normally those taken within
your actual production mix, with all the caching and resource
competition which goes along with that.

-Kevin