RE: LOB Operation and SQL*Net Message From Client and cursor #0

From: Jonathan Lewis <jonathan_at_jlcomp.demon.co.uk>
Date: Wed, 1 May 2013 10:08:17 +0000
Message-ID: <CE70217733273F49A8A162EE074F64D90D021D_at_exmbx06.thus.corp>


You may have covered this in an email I missed, but if you're testing from SQL*Plus then

  1. the arraysize is ignored if you actually fetch the LOB
  2. if you set longchunksize to be less than long (the defaults are 80 each) then you get multiple LOBREAD passes for each lob fetch, for example if you set long 20000 and leave longchunksize to 80, and have LOBs of 4,000 bytes you will see 51 (seems like one to many) calls to LOBREAD. The LOBREAD calls can be very quick - which can lead to all sorts of unaccounted time and granularity errors at all the different stages of monitoring. Possibly the application has a similar pair of configuration options.

Regards
Jonathan Lewis



From: oracle-l-bounce_at_freelists.org [oracle-l-bounce_at_freelists.org] on behalf of Larry Elkins [elkinsl_at_verizon.net] Sent: 30 April 2013 23:10
To: 'Mark W. Farnham'; 'Oracle-L'
Subject: RE: LOB Operation and SQL*Net Message From Client and cursor #0

> So a lot of the time is spent on the line turn-around, and both tools count that latency against the
> other guy.

Correct, the guy using opnet is saying that turn from the app server layer to the db and back is all on the DB, next to nothing on the network itself, and not much with regards to client think time on the client. And of course tracing is saying mostly sql*net message from client, the time to stuff the data in the tcp buffer, go down the wire, client think time, and come back up. And it's not my place to say his tool is wrong and 10046 is right ;-) Maybe they both are right and it's in a virtualization layer that is hit after the NIC. It's something we are considering, though I don't have the skills or knowledge to dig into that, someone else will have to go there.

>
> Can you use a bigger packet?
> Can you try placing your client process directly on the dbserver?

Can't get the client code there, but taking the SQL statement in question, the one driving all the elapsed time, I run SQL*Plus on the server, both through SQL*Net and bypassing SQL*Net, array size 100 like they do, and "set autotrace trace stat" to discard the rows and not eat time rendering them on the screen, and the processing time drops to 1/10 what it was within the application, with the actual DB time about the same. Unaccounted for time was also similar, though percentage wise constituted a much larger slice of total time.

When repeating with SQL*Plus on a desktop, the total timings came more in line with what we see with the application, though the unaccounted for time went up compared to SQL*Plus on the server. The fetch calls match up with the array size, it's just those OPI level trips where we add a lot more trips into the mix, and don't show up on the cursor's fetch count.

>
> One last thing: Usually tracing on is a minor side effect, but if there is a throughput challenge on
> your trace/output directory and your only wait is a long stream of message waits, that could add up to
> significance. So carefully compare the times traced and untraced to rule this out.

Your comments did make me think about going back and looking at unaccounted for time (something, maybe Tanel posting, about those OPI calls work not being counted anywhere). And timing is the same without tracing.-- http://www.freelists.org/webpage/oracle-l Received on Wed May 01 2013 - 12:08:17 CEST

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