Re: Why we should use bind variables when we write code......

  • From: Wolfgang Breitling <breitliw@xxxxxxxxxxxxx>
  • To: Mark.Bobak@xxxxxxxxxxxxxxx
  • Date: Tue, 19 Sep 2006 22:24:44 -0600

Just be sure to not go overboard and heed the warnings in the (Oracle10.1) Performance Tuning Guide:

"The shared pool is also able to support unshared SQL in data warehousing
applications, which execute low-concurrency, high-resource SQL statements. In this
situation, using unshared SQL with literal values is recommended. Using literal values
rather than bind variables allows the optimizer to make good column selectivity
estimates, thus providing an optimal data access plan."
"When bind variables are used in a statement, it is assumed that cursor sharing is
intended and that different invocations are supposed to use the same execution plan. If
different invocations of the cursor would significantly benefit from different execution
plans, then bind variables may have been used inappropriately in the SQL statement."

At 08:37 AM 9/19/2006, Bobak, Mark wrote:

So, last week, one of my instances starts getting ORA-4031s, and after a few minutes, comes crashing down when a background process (lmd0, I think it was) catches an ORA-4031. So, with the instance down, it's a bit tough to see what happened. So, we start things up again, and I start watching closely over the next few days. Seems there's lots of code that doesn't bother with binds. In some cases, there are a dozen non-sharable SQLs that are identical except for literals, in other cases, up to hundreds. (Thanks to T.Kyte for the script that I'm using to identify non-sharable SQL.) After a few days, I find the smoking gun. One single SQL statement that has 3,424 copies that are identical except for literals. (No, that's not a typo.) This is taking up abour 75% of the 475M of shared pool that's dedicated to the sql area. One single SQL statement, 75%. Yikes!

So, now I'm on an education kick. "This is the way we do things when we don't want to kill the Oracle database server!"

So, my question is, is there a resource, online or otherwise, that has examples of proper bind variable usage in various languages? I can cover C/Pro*C, PL/SQL, SQL*Plus, but what about Java, Perl, Python, etc,etc? I'm not much of a coder lately, and I want proper examples that can be shown to developers, in whatever is the language of choice.


Wolfgang Breitling
Centrex Consulting Corporation

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