Overview Of Cics And Db2 Interface

I.T.TRAININGS

Overview of CICS and DB2 Interface Course designed and Conducted by Sunderrajan Iyer [email protected] Jul 17, 2009

Overview of CICS and DB2 Interface

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CICS attachment facility

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• A CICS attachment facility is provided with CICS that allows you to operate DB2 with CICS. – The connection between CICS and DB2 can be created or terminated at any time, and CICS and DB2 can be started and stopped independently. – You also have the option of CICS automatically connecting and reconnecting to DB2. – The DB2 system can be shared by several CICS systems • But each CICS system can be connected to only one DB2 subsystem at any one time.

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Overview of CICS and DB2 Interface

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Attachment Commands • Attachment commands display and control the status of the attachment facility and are issued using the supplied CICS transaction DSNC. DSNC • The attachment commands are: – – – – –

STRT - start the connection to DB2 STOP - stop the connection to DB2 DISP - display the status of the connection to DB2 MODI - modify characteristics of the connection to DB2 DISC - disconnect threads

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More on Attachment Facility

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• The CICS DB2 attachment facility provides a multithread connection to DB2 – There is a thread for each active CICS transaction accessing DB2 – Threads allow each CICS application transaction and DB2 command to access DB2 resources • Application Plan

– Each thread, used by a CICS transaction, or by a command, runs under its own subtask task control block (TCB). – A thread is defined based on the specifications in RDO when a transaction issues the first SQL statement – If a existing thread is available, it is used before creating a new thread

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Overview of CICS and DB2 Interface

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Types of Threads • Command Threads – These are reserved to be used by the DSNC transaction

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• Entry Threads – They are intended to be used by transactions • If defined as protected, they are not terminated when no CICS transaction is using them • If defined as unprotected, they are terminated if no CICS transaction is using them

• Pool Threads – They are used for all transactions not using Entry or Command thread – They are intended for low volume transactions, and as a overflow from command and entry threads

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Overview of CICS and DB2 Interface

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How CICS interacts with DB2

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• The CICS DB2 attachment facility provides CICS applications to access DB2 database while operating in the CICS environment – The application can access both CICS and DB2 data at the same time

• CICS co-ordinates recovery of both DB2 and CICS data when a failure occurs

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Overview of CICS and DB2 Interface

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How CICS interacts with DB2

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Overview of CICS and DB2 Interface

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Address Spaces in DB2 • • • • •

DSN1MSTR: System Service Component DSN1DBM1: Database Service Component DSN1DIST : Distributed Service Component IRLMPROC : Resource Lock Manager DSN1SPAC: For DB2 stored procedures

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How a CICS Task works with DB2 • When an application program issues its first SQL request the CICS resource manager interface (RMI) processes the request and passes control to the attachment facility's task related user exit (TRUE). • A transaction thread is scheduled by the CICS attachment facility, and at this stage DB2 checks authorization, creates control blocks and allocates the application plan. • When the SQL request completes DB2 passes data back to the CICS attachment facility, and the CICS task regains control until the CICS transaction issues another SQL request. • Finally, the CICS attachment facility returns control to the CICS application program. Jul 17, 2009

Overview of CICS and DB2 Interface

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How a CICS Task works with DB2

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Overview of CICS and DB2 Interface

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Resource Control Table • In releases of CICS prior to Transaction Server for OS/390 V1 R2, the connection between CICS and DB2 was done using resource control table • The resource control table contains relationship between CICS transactions and the resources it requires – Application Plans

• It is generated using DSNCRCT macro provided by CICS attachment facility

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Resource Definition Online • CICS TS R3, no longer supports RCT entries defined using DSNCRCT macro • You have to use Resource Definition Online facility of CICS TS R3 • Using RDO following objects can be created – DB2CONN: Defines the global attributes of the CICS DB2 interface and defines the attributes of pool threads and command threads – DB2ENTRY: Defines entry threads to be used by a specific transaction or group of transactions – DB2TRAN: Defines additional transactions to be associated with a particular DB2ENTRY

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Overview of CICS and DB2 Interface

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Main activities in SQL processing • You should select the thread type to use for a given set of transactions together with the BIND parameters for the corresponding plan. • This is because the BIND parameters determine whether a number of activities are related to the thread or to the transactions. • The main DB2 activities involved in processing CICS transactions with SQL calls are – – – –

Create a thread or reuse an existing thread. Process the SQL statements. Perform commit processing. Terminate the thread or keep it.

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Overview of CICS and DB2 Interface

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Main activities in SQL processing

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• These main activities are performed for each transaction. • The most important options are: – DB2CONN and DB2ENTRY specifications • Use of protected entry threads • Use of unprotected entry or pool threads • Authorization strategy

– BIND options • ACQUIRE • RELEASE • VALIDATE

– Use of PACKAGES

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