A question about waits

Question

Hi,
We are on Oracle 10.2.0.4 on Solaris 10.
In my awr report I have the following among top five top wait event:
Wait event
SQL*Net more data to client 14,022,144 3,758 0 17.7 Network
Edited by: orausern on Apr 15, 2010 5:07 AM

Answer 1

Your average wait on "more data to client" is very small.
The number of calls is large - but you don't have any real measure of its significance and meaning.
You need to look at Instances statistics:
SQL*Net roundtrips to/from clien         17,407,740        9,876.1          32.6
bytes sent via SQL*Net to client      4,429,719,421    2,513,152.0       8,303.4A round-trip consists of one 'sql net data to client' plus ALL the ' more data to client' that took place at the same time, so:
Compare your count of 'more data to client' with roundtrips - if it is a large multiple you can infer that on average each round trip is a large chunk of data that has to be sent as several packets, and you probably need to make your SDU larger. If you look at 'bytes sent via SQL net to client' compared to roundtrips, you get an idea of the size of the the "average" packet - hence an indication of the necessary size of the SDU.
There are also a couple of tcp network configuration parameters that may need setting. I never remember the exact names, but it's something like 'tcp_transmit_buf' and 'tcp_recv_buf'. This is the volume of data that the tcp layer can send before it needs an ACK from the far end. So, for example, if your SDU is 32K and your tcp buffer size was only 4KB, then Oracle would send one packet of 32KB, tcp would handle as 8 chunks of 4KB - with 8 tcp ACKs from the far end, and the (because tcp works in line packets of about 1400 bytes - each 4KB would go as 3 packets with an ACK expected on the third). So you need the tcp buffer sizes to be slightly larger than the SDU for best effect.
(If your procsses parameter is large, though, the total tcp buffer memory needed is processes * tcp buffer size).
Regards
Jonathan Lewis
http://jonathanlewis.wordpress.com
http://www.jlcomp.demon.co.uk
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