Re: 3 round trips over network for simply "select sysdate from dual"

Hi,
Is your client app checking to see if there are any more rows to get form the sever or doing some kind of extra query so that it has a description of the table you are querying, I understand that PERL DBI/DBD does the latter by default.

Regards

Pete

On Fri, Jun 20, 2008 at 10:13 AM, qihua wu <staywithpin_at_gmail.com> wrote:

> Hi, all
>
> When using tcpdump to check what happen over the network when do a simple
> query as
> SQL> select sysdate from dual;
>
> SYSDATE
> ---------
> 20-JUN-08
>
> The tcpdump is as following, 3 round trips between the server and client.
> Why so many trips? Don't we only need to 1 round trip as client send the
> query and the server reply?
>
> 16:56:13.354672 IP host1 > host2.1580: . 7898:8 054(156) ack 6755 win 32768
> 16:56:13.354683 IP host2.1580 > host1: . 6755:6 836(81) ack 8054 win 32768
> 16:56:13.521731 IP host1 > host2.1580: . 8054:8 126(72) ack 6836 win 32768
> 16:56:13.521744 IP host2.1580 > host1: . 6836:6 853(17) ack 8126 win 32768
> 16:56:13.688967 IP host1 > host2.1580: . 8126:8 141(15) ack 6853 win 32768
> 16:56:13.688980 IP host2.1580 > host1: . 6853:6 874(21) ack 8141 win 32768
>
>
> And the expert says below: one additional roundtrip to initiate the query.
> Don't quite understand why we need additional roundtrip to initiate.
> http://www.adp-gmbh.ch/ora/sqlplus/arraysize.html
>
> Thanks,
> Qihua
>

-- 
Regards

Pete

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