Re: Oracle Data Guard

From: Yong Huang <yong321_at_yahoo.com>
Date: Thu, 11 Dec 2003 11:49:25 -0800
Message-ID: <F001.005D991B.20031211114925@fatcity.com>

Hi, Jonathan,

I think your question is why I mentioned TDU, not just SDU, in my response to Guang's message. I admit I didn't give much thought and threw that in. Note:44694.1 says it's set to 32k by default and its adjustable range is 0 to 32k. Then the question is why Oracle chose the magical 32k. Would changing it to anything else yield any SQL*Net performance gain? It won't be too much extra work for Guang Mei to find out while he's experimenting with SDU.

It's a little confusing when you say TDU is MTU, because, I think, the term MTU (Maximum transmission unit) is already used by network engineers to refer to the maximum number of bytes a data link layer frame can contain (1500 bytes for Ethernet e.g.). But I understand what you mean.

Regarding a less than maximum SDU size, maybe it's useful if most of the SQL result is much less than 32k? Somebody can experiment and find out.

Yong Huang

Jonathan Lewis wrote:

Can you clarify a couple of points for me.

The SDU (session data unit) is presumably the packet size that the Oracle client and server want to pass back and forth - which is presumably the maximum size the one synchronous dialogue unit will be.

The TDU (transport data unit) is presumably the predicted size of the transport maximum unit of data transfer (MTU).

Why does Oracle need to know anything about the underlying transport mechanism ?
If I set the SDU to the largest legal value (possibly 32K, perhaps 64K) the server task switch will occur after building and sending that packet - is there any good reason why I shouldn't do that. After all, if the transport simply accepts the 64K packet and gets it to the other end of the wire (not yet to the client session, just to the receiving transport layer) as rapidly as possible does it matter to Oracle whether the transport is using 1.5K or 8K packets. The fact that the transport layer doesn't have to work its packet synchronously means that some overheads have disappeared as far as Oracle is concerned.

Regards

Jonathan Lewis

> Hi, Guang,
>
> Look up SDU and TDU in Oracle documentation Network configuration. You set
them
> in tnsnames.ora and listener.ora, not sqlnet.ora. protocol.ora allows you to
> modify some procotol-specific parameters. In addition, in your client
> application, you can choose a sensible array fetch size, such as arraysize in
> sqlplus (in fact, sqlplus arraysize changes more than just network data chunk
> size). You can't magically increase the network transfer rate by lowering
> network latency. But you can indirectly increase the rate by other means,
such
> as buffering slightly more data in one chunk.
>
> Yong Huang

Do you Yahoo!?
New Yahoo! Photos - easier uploading and sharing. http://photos.yahoo.com/

-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.net
-- 
Author: Yong Huang
  INET: yong321_at_yahoo.com

Fat City Network Services    -- 858-538-5051 http://www.fatcity.com
San Diego, California        -- Mailing list and web hosting services
---------------------------------------------------------------------
To REMOVE yourself from this mailing list, send an E-Mail message
to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in
the message BODY, include a line containing: UNSUB ORACLE-L
(or the name of mailing list you want to be removed from).  You may
also send the HELP command for other information (like subscribing).

Received on Thu Dec 11 2003 - 13:49:25 CST