topic %wcache tuning in Operating System - HP-UX

%wcache tuning

T G Manikandan — Sat, 05 May 2001 06:47:43 GMT

Hello,
The %wcache on my L-class server with two processors gives a value below 60.
I have gone through some sun documents which tells that the wcache should not be below 75%.
How can I improve the perfomance if I am right?
Please provide some solutions.
Thanks.
Manikandan

Re: %wcache tuning

Thierry Poels_1 — Sat, 05 May 2001 07:07:30 GMT

Hi,
the success of the write-cache depends on your application(s).
If you are using the dynamic buffer cache, the check if dbc_min_pct and dbc_max_pct are not set to low (shouldn't be to high eiter :).
If you are using a database like Oracle, dbc_max_pct should be rather low, because Oracle uses its own buffer.
regards,
Thierry.

Re: %wcache tuning

Thierry Poels_1 — Sat, 05 May 2001 07:27:10 GMT

...then check... ...too low... ...too high...

me? spelling/typing mistakes?? never! hmmmz ;)))

Re: %wcache tuning

T G Manikandan — Mon, 07 May 2001 02:32:41 GMT

Hello,
Thanks for the reply.
I went throught the dbc_max and dbc_min and it was 50 and 5 respectively.
I have three databases running on the machine.
Is there a need to modify the dbc_max?
Thanks.
Manikandan

Re: %wcache tuning

Thierry Poels_1 — Mon, 07 May 2001 06:11:49 GMT

sjips, eiter --> either; it was really too early when I typed that message ;)

If it's an Oracle database server dbc_min_pct and dbc_max_pct can be set both to 2. Check your database cache hit rate, it should be close to 90% or above, and don't worry too much about OS write cache. (don't know about other databases though, which are you using?).
50 and 5 are the default, but this might create a buffer cache using half of your memory.
good luck,
Thierry.