RAC, SELECT FOR UPDATE, connection pools

  • From: "Herring Dave - dherri" <Dave.Herring@xxxxxxxxxx>
  • To: <oracle-l@xxxxxxxxxxxxx>
  • Date: Fri, 12 Feb 2010 07:46:18 -0600

I'm wondering if I could get a little more detail about what Martin listed 

'"select for update" as soon as a user modified data.  This was in a connection 
pool... That obviously wasn't too great.'

I'm supporting a env on Linux, involving a 4-node RAC with matching 
DG.  It's an OLTP db with app servers using connection pools, where I'll see 
unbalanced batches of connections coming in (2000 on 1 node, 80 on another), 
which eventually even out across the servers.  I also see frequent "SELECT ... 
FOR UPDATE" statements.

I'm relatively new to this env and really struggle in getting details on how 
the apps are working, so when I saw the quote above from Martin I figured I'd 
jump at getting more details on other's experiences with this type of 

I think to start I'm just looking for issues you've run into, as again, I get 
very little detail out of the app team in terms of what they're doing and how 
things are configured.

I realize this is really directed towards Martin Bach, but I figured I'd post 
to the group in case anyone has a similar setup.  I'm pretty much having to 
reverse engineer the whole app to know what's going on, which is such a treat. 


Dave Herring  | DBA, Global Technology Services
A c x i o m  C o r p o r a t i o n
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Service Desk: 888-243-4566, https://servicedesk.acxiom.com, GSCA@xxxxxxx

-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On 
Behalf Of Martin Bach
Sent: Thursday, February 04, 2010 6:00 AM
To: mwf@xxxxxxxx
Cc: veeeraman@xxxxxxxxx; 'Guillermo Alan Bort'; 'Thomas Roach'; 'ORACLE-L'
Subject: Re: RAC for dev env

I can only second that email from Mark!

Developing against single instance when prod is RAC - I can't count the
number of times I have seen developers code against single instance
Oracle (and maybe even a subset of production data only), release the
new code which then promptly fails to scale/work in RAC?

I dealt with an application development "framework" once that
dynamically changed to "select for update" as soon as a user modified
data. This was in a connection pool... That obviously wasn't too great.

Also don't forget that you might actually _have_ to invoke DR and then
you could be hit big time for not running in a RAC configuration. I only
hope that has been figured into the equation or somebody from high up
acknowledges that.


Martin Bach
OCM 10g

On 02/03/2010 08:44 PM, Mark W. Farnham wrote:
> So I believe your management dictated constraints are: RAC for prod,
> single instance databases for everything else.

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