db2 bind on luw

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Binding embedded SQL packages to a database



Binding is the process of creating a package from a bind file and storing it in a database.

Application, bind file, and package relationships
Database applications use packages for some of the same reasons that applications are compiled: improved performance and compactness. By precompiling an SQL statement, the statement is compiled into the package when the application is built, instead of at run time. Each statement is parsed, and a more efficiently interpreted operand string is stored in the package. At run time, the code generated by the precompiler calls run-time services database manager APIs with any variable information required for input or output data, and the information stored in the package is executed.
The advantages of precompilation apply only to static SQL statements. SQL statements that are executed dynamically (using PREPARE and EXECUTE or EXECUTE IMMEDIATE) are not precompiled; therefore, they must go through the entire set of processing steps at run time.

With the DB2® bind file description (db2bfd) utility, you can easily display the contents of a bind file to examine and verify the SQL statements within it. You can also display the precompile options used to create the bind file using the DB2 bind file description (db2bfd) utility. This can be useful in problem determination related to the bind file for your application.
You can set the STATICASDYNAMIC string on the GENERIC parameter of the BIND command to "yes" to instruct the DB2 database manager to store all statements in the catalogs and mark them as incremental bind. At run time, when the package is first loaded, the database manager uses the current session environment (rather than the package) to set up the section entries and other entities (text is populated and the package cache is accessed). Thereafter, the statements in the bound file behave the same as they would if you were using dynamic SQL. For example, sections will be implicitly recompiled for Database Definition Language invalidations, special register updates, and so on. The DB2 database manager provides this feature to facilitate the migration of embedded SQL C applications from other database systems.

• Effect of DYNAMICRULES bind option on dynamic SQL
  The PRECOMPILE command and BIND commandparameter DYNAMICRULES determines which rulesapply to dynamic SQL at run time.
  
• Using special registers to control the statement compilation environment
  For dynamically preparedstatements, the special registers can be specified to define the statementcompilation  environment.
  
• Package recreation using the BIND command and an existing bind file
  Binding is the processthat creates the package the databasemanager needsto access the database when the application is executed.
  
• Rebinding existing packages with the REBIND command
  Rebinding is the processof recreating a package for an application program that was previouslybound. You must rebind packages if they were marked invalid or inoperativeor if the database statistics changed since the last binding.
  
• Bind considerations
  Ifyour application uses a code page that differs from the database codepage, you must ensure that the code page used by the application iscompatible with the database code page during the bind process.
  
• Blocking considerations
  When you want to turn blocking off for an embedded SQLapplication and the source code is not available, the applicationmust be rebound using the BIND command and settingthe BLOCKING NO clause.
  
• Advantages of deferred binding
  Precompiling with bindingenabled allows an application to access only the database used duringthe precompile process. Precompiling with binding deferred, however,allows an application to access many databases, because you can bindthe BIND file against each database.
  
• Performance improvements when using REOPT option of the BIND command
  The bind option REOPT can significantlyimprove the embedded SQL application performance.
  

Related reference:

db2bfd - Bind file description tool command
EXECUTE statement
PREPARE statement
Concept topic