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Monday, April 19, 2010

Using DB2 Stored Procedures, Part 2: The Static SQL Angle

This is the second of a three-part entry on various factors you could consider in determining how (or whether) DB2 stored procedure technology might be employed in your organization's application environment. In part one I described some advantages associated with client-side and server-side SQL and pointed out that, if you like your SQL on the database server side of things (and I do), DB2 stored procedures provide a very useful means of going that route. In this entry I'll examine stored procedure usage in a static SQL context. In part three, I'll look at how your use of stored procedures might be influenced by your desire for more, or less, database schema visibility from an application development perspective.

The pros of static SQL. Static SQL is, as far as I know, an exclusively DB2 concept, so if you're kind of new to DB2 you might want to check out the blog entry that I posted a few weeks ago, on the basics of SQL (including static SQL) in DB2-accessing programs. Those of you who are familiar with static SQL probably know that it delivers two important advantages versus dynamic SQL:
  • Better performance -- In particular, I'm talking about the database server CPU consumption aspect of application performance. The CPU efficiency advantage delivered by static SQL is, of course, based on the fact that preparation of static SQL statements (referring to preparation for execution by DB2, which includes things such as data access path selection by the DB2 optimizer) is accomplished before the statements are ever issued for execution by the associated application program. This is important because for some simple, quick-running SQL statements, the CPU cost of statement preparation can be a several times the cost of statement execution. Can dynamic statement caching reduce the database-server-CPU-cost gap between static and dynamic SQL? Yes, but even if you have repeated execution of parameterized dynamic SQL statements (so as to have a high "hit ratio" in the prepared statement cache), generally the best you can hope for is database server CPU consumption that approaches -- but doesn't match -- the CPU cost of an equivalent static SQL workload (the effectiveness of dynamic statement caching gets a boost with DB2 10 for z/OS, which provides for better prepared statement cache matching for dynamic SQL statements that include literal values -- versus parameter markers -- in query predicates).
  • More-robust security -- For a dynamic SQL statement to execute successfully, the authorization ID of the application process issuing the statement has to have read (for queries) and/or data-change privileges on the tables (and/or views) named in the statement. Such is not the case for a static SQL statement. All that is needed, authorization-wise, for successful execution of a static SQL statement is the execute privilege on the statement-issuing program's DB2 package.
Now, I'll concede that there are times when dynamic SQL is a very good choice for an application program. A developer at one of my clients had to write a program that would retrieve information from a DB2 database according to a combination of search arguments that a user could enter on a screen. There were quite a few search options, and coding a static DECLARE CURSOR statement for every possible combination would have been a major piece of work. The developer opted instead to have his program build the SELECT statement dynamically, based on the choices entered by the user. This was a good choice, as it enabled him to deliver the needed functionality in a much more timely manner than would have been the case had he opted for the static SQL approach. Still, with exceptions such as this one duly noted, my preference is to go with static SQL in most cases, especially in OLTP and batch application environments (dynamic SQL often dominates in a data warehouse system, and that's OK).

Can static SQL statements be issued from client-side application programs? The answer to that question depends on the programming language used. If a client-side program is written in assembler, C, C++, COBOL, Fortran, PL/I or REXX, it can issue static SQL statements (for assembler and PL/I, the client platform has to be a mainframe). If the language is Java, static SQL can be used by way of SQLJ. Another Java option for static SQL is IBM's Optim pureQuery Runtime product, which can also enable the use of static SQL when client-side programs are written in VB.NET or C#. If the language used on the client side is Perl, Python, PHP, or Ruby, the only possibility is dynamic SQL.

This is where DB2 stored procedures come in. Suppose you want to use static SQL for your application, but you want to use, say, Ruby on the client side? Or, suppose you're using Java on the client side, but your Java developers don't want to use SQLJ (and you don't have Optim pureQuery Runtime)? Well, how about putting the static SQL in DB2 stored procedures, and having your client-side programs invoke these by way of dynamic CALLs? You get the performance and security benefits of static SQL, and your client-side developers get to use their language (and data-access interface) of choice. Everybody's happy!

That's reason number two for using DB2 stored procedures: they provide a means whereby static SQL can be easily -- and dynamically, if needs be -- invoked by client-side programs. Stop by the blog again soon for my reason number three.

2 Comments:

Blogger midibu said...

You remark that "the effectiveness of dynamic statement caching gets a boost with DB2 10 for z/OS, which provides for better prepared statement cache matching for dynamic SQL statements that include literal values -- versus parameter markers -- in query predicates".

Does this mean that, run via a prepared statement from a Java program, a query like this isn't a candidate for caching:
select user_id, user_name from sometable where status = 'ACTIVE' and user_name like ?

April 24, 2010 at 9:00 AM  
Blogger Robert Catterall said...

Here's what I mean. Consider a statement like this:

SELECT TOTAL_AMOUNT
FROM ORDERS
WHERE ORDER_NUM = 1234

Before DB2 10 for z/OS, that statement wouldn't be considered a prepared statement cache match with this one, because of the different literal value in the predicate:

SELECT TOTAL_AMOUNT
FROM ORDERS
WHERE ORDER_NUM = 6789

In a DB2 9 (or prior) environment, the statements would have been matches had they been coded this way:

SELECT TOTAL_AMOUNT
FROM ORDERS
WHERE ORDER_NUM = ?

My understanding is that, in a DB2 10 environment, the first two example statements above (the ones that differed only in the literal values coded in the predicate) would be matches with respect to the prepared statement cache.

Robert

April 26, 2010 at 6:46 AM  

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