Re: Does oracle db serialize concurrent read-only SELECT ?

From: Jung Tjong <jtjong_at_cisco.com>
Date: Wed, 18 Apr 2001 12:31:47 -0700
Message-ID: <3ADDEBA3.81C413A8@cisco.com>

Jonathan,

The only events I saw for the sessions are SQL*Net message to and from client
and no file related events.
Here is for one of the 5 sessions I created:

       SID EVENT

---------- ------------------------------------------------------

TOTAL_WAITS TOTAL_TIMEOUTS TIME_WAITED AVERAGE_WAIT MAX_WAIT ----------- -------------- ----------- ------------ ----------

        12 SQL*Net message to client
       1504              0           0            0          0

        12 SQL*Net message from client
       1503              0         393   .261477046         60

The numbers that seem large is the total_waits for all events and time_waited
for the message from client event.
For the 5 sessions, total_waits is 1504 for the "to client" and 1503 for the "from client".
The time_waited for the "from client" ranges from 3xx to 5xx. I don't know the significance of these numbers. Do they look normal ?

Jonathan Lewis wrote:

> Set timed_statistics = true, then start each
> session, run the test, then do a listing of
> v$session_event for the session. Order
> by total wait time (descending), and see
> if this tells you where most of the time was
> lost. List the max-wait-time as well.
>
> There is a bug with VxFS and concurrent
> file reads (pread64()) that results in severe
> contention and wait times; I wonder if that
> might be the problem.
>
> --
> Jonathan Lewis
> Yet another Oracle-related web site: http://www.jlcomp.demon.co.uk
>
> Practical Oracle 8i: Building Efficient Databases
> Publishers: Addison-Wesley
>
> Reviews at: http://www.jlcomp.demon.co.uk/book_rev.html
Received on Wed Apr 18 2001 - 14:31:47 CDT