The more significant changes for this edition are:
Technical changes: Open transaction environment (OTE)
exploitation
- If your CICS system is connected to DB2 Version 6 or later, CICS now
exploits the open transaction environment (OTE) to improve performance by
reducing TCB switching. For full details of the CICS DB2 configuration needed
to exploit the open transaction environment, see Migrating to a different release of DB2.
- For an overview of the effects of this change, see the CICS® Transaction Server for z/OS® Release Guide for CICS Transaction Server for z/OS, Version 2 Release 2. Overview of the CICS DB2 interface, has explanations of the important differences in the way
CICS connects to DB2 in the open transaction environment, including the use
of open TCBs instead of subtask TCBs to run threads (see Overview: How threads work). Thread TCBs (task control blocks) has further information on open TCBs being used as thread
TCBs, and on the new modules used to control CICS DB2 connection processing. How threads are created, used, and terminated explains the differences in thread use when using open TCBs.
- When using the open transaction environment, to be sure that you have
enough open TCBs available to process your DB2 workload, ensure that the limit
set in your MAXOPENTCBS system initialization parameter is greater than the
limit set in the TCBLIMIT attribute of your DB2CONN definition. For more information,
see The MAXOPENTCBS system initialization parameter and TCBLIMIT.
- To gain the performance benefits of the open transaction environment,
application programs must be threadsafe. See Enabling CICS DB2 applications to exploit the open transaction environment
(OTE) through threadsafe programming for information.
- OTE exploitation is particularly important for enterprise beans that make
DB2 requests. See Using JDBC and SQLJ in enterprise beans: special considerations for information.
- There is a new wait type for the open transaction environment, CDB2CONN,
and some of the existing wait types only apply when CICS is not using the
open transaction environment (when it is connected to DB2 Version 5 or earlier).
See Wait types for CICS DB2 for information.
- The use of the open transaction environment affects how you can purge
CICS DB2 transactions. See Purging CICS DB2 transactions for information.
- There are differences to the tracing performed for the CICS DB2 attachment
facility in the open transaction environment. Among other things, the CICS
DB2 connection program DFHD2D2, which replaces DFHD2EX3 in the open transaction
environment, makes new entries in the CSUB trace table. See Trace for CICS DB2 for
information.
- There are changes to accounting and performance monitoring as a result
of the availability of the open transaction environment. See Accounting and monitoring in a CICS DB2 environment for
information.
Technical changes: Group attach
- If your CICS system is connected to DB2 Version 7 or later, you can now
use the DB2 group attach facility, which allows CICS to connect to any one
member of a data sharing group of DB2 subsystems, rather than to a specific
DB2 subsystem. For full details of the CICS DB2 configuration needed to use
the DB2 group attach facility, see Migrating to a different release of DB2.
- See Using the DB2 group attach facility for more information about the group attach
facility. Group attach is controlled by the new DB2GROUPID and RESYNCMEMBER
attributes of the DB2CONN definition -- see the CICS Resource Definition Guide for
full descriptions of these attributes. If you are using group attach, this
affects the resolution of indoubt units of work, and you need to decide on
the strategy that CICS adopts -- see Resolving indoubt units of work (UOWs) for details.
- If you are using group attach, the output from, and use of, the DSNC STRT
command is affected -- see DSNC STRT for information. If
you specify a DB2ID on a DSNC STRT command, this overrides and blanks out
a DB2GROUPID set in the installed DB2CONN definition. You cannot specify a
DB2GROUPID on a DSNC STRT command.
Other technical changes
- When running with DB2 Version 7 or later, Java applications and enterprise
beans for CICS can use the new Java Database Connectivity (JDBC) driver provided
by DB2, that supports a selected subset of the JDBC 2.0 API, including support
for the DataSource interface. A DataSource is an alternative way of obtaining
a JDBC connection to a database. Using JDBC and SQLJ to access DB2 data from Java programs and enterprise
beans written for CICS has information on
the requirements for the JDBC 2.0 driver, and on using the DataSource interface
to acquire connections. Samples are provided to set up a CICS-compatible DataSource.
- In this release of CICS, PLAN and PLANEXITNAME options are added to the
INQUIRE DB2TRAN command, so you can find out in a single step which plan is
used by a specified transaction or set of transactions, or which transactions
use a specified plan. See the CICS System Programming Reference for information.
- The output from the DSNC DISPLAY PLAN or TRAN command now distinguishes
between a thread that is active and currently executing in DB2, and a thread
that is active but is not currently executing in DB2. See DSNC DISPLAY for
information.
- When preparing CICS programs that access DB2, you can now use Language
Environment-conforming language compilers (COBOL and PL/I) that support the
integrated CICS translator and, depending on your release of DB2, an SQL statement
coprocessor. See CICS DB2 program preparation steps for more information on the changes
to the program preparation process.
Structural changes
- Overview of the CICS DB2 interface, has been rewritten, and now includes information
on
- how threads and thread TCBs work
- how the DB2CONN, DB2ENTRY and DB2TRAN definitions work together
- how plans, packages and dynamic plan exits work
- Application design and development considerations for CICS DB2 and Preparing CICS DB2 programs for execution and production have been reorganised.
In particular, Using JDBC and SQLJ to access DB2 data from Java programs and enterprise
beans written for CICS is now a separate chapter.
- Installation and migration notes for CICS DB2 and Defining the CICS DB2 connection have been reorganised.
- The chapter 'Customization: dynamic plan exits' has been removed, and
the information it contained is now in Dynamic plan exits and Dynamic plan switching.
- The chapter 'Monitoring, tuning and handling deadlocks' has been removed.
The information it contained is now in Accounting and monitoring in a CICS DB2 environment, Preparing CICS DB2 programs for execution and production, Problem determination for CICS DB2, and the CICS Performance Guide.
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