IMS Fundamentals - Connecting to other Subsystems

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Connecting IMS to Other Subsystems


Objectives

• Learn about IMS Multiple Systems Coupling (MSC)• Learn about IMS/CICS/VTAM Inter System Communication

(ISC)• Understand how IMS TM Transactions can access DB2 as an

external Database manager• Understand how CICS Transactions can access IMS as an

external Database manager• Learn how a Two Phase commit process is used when IMS

Databases are accessed by CICS transactions


IMS ( A )

San Francisco

IMS ( B )

Chicago

IMS ( C )

New York

Local Databases

Local Databases

Local Databases

Distributed Databases


IMS ( A )

Head Office

IMS ( B )

Sales Office

IMS ( C )

Plant Office

Distributed Applications


IMS ( A )

IMS ( D) IMS (F)

Increased Capacity

IMS ( E )


Multiple Systems Coupling (MSC)

• Allows for the distribution of IMS transactions between IMS subsystems– Transactions entered from one IMS subsystem may be processed on

another IMS subsystem• IMS-to-IMS configuration only

– Each system is a complete IMS subsystem• Transactions may be "routed" via:

– SNA VTAM SDLC Link– Channel-to-Channel (CTC) Adapter– Main Storage-to-Main Storage (MTM) Link (within one z/OS image)

• Routing is automatic via IMSGEN process– No application program or end-user need be involved


IMS ( A )

MSGQ

VTAM

SystemLog

MessageQueue

IMS ( B )

MSGQ

VTAM

SystemLog

MessageQueue

MSC Message Routing

• Destinations are modifiable via user exits:– Too many, or duplicate names– Destinations chosen dynamically

• Each subsystem has its own MTO and OLDSs


IMS ( A )

VTAM

N C P

IMS ( B )

VTAM

N C P

User-written Program

VTAM

N C P

CICS/TS

VTAM

N C P

CICS/VSE

VTAM

ICA

SNA

Inter-System Communication (ISC)


IMS ( A )

TRAN1

GU

ISRTALT-PCB

ISRT

IMS ( B )

TRAN2

GU

TRAN1

MSGQ MSGQ

DL/IDB( S )

ISC Message Routing (1 of 2)


IMS ( A )

TRAN1

GU

ISRTTRAN2

IMS ( B )

TRAN2

GU

ISRT

TRAN1

MSGQ MSGQ

DL/IDB( S )

ISC Message Routing (2 of 2)


CICS

TRAN1

EXEC CICSSTART

TRAN2...

EXEC CICSRETRIEVE..

TRAN3

EXEC CICS SEND..

EXEC CICSRETRIEVE..

TRAN4

IMS

TRAN2

GU

ISRT

TRAN5

GU

ISRT

DL/IDB( S )

CICS-IMS Connectivity

• CICS-to-IMS scenarios:


IMS ( A ) IMS ( B )

RYO VTAMPROGRAM

MULTIPLE SYSTEMS COUPLING (MSC):

COMMUNICATIONS LINE

CHANNEL-TO-CHANNEL

MEMORY-TO-MEMORY

CICSIMS ( C )

INTER-SYSTEM COMMUNICATION (ISC):DATABASES DATABASES

MSGQMSGQ

MSC / ISC Summary


DCCTL Region Type

• Like an IMS Transaction Manager Region without the databases

• Two primary uses:– Use as a router in a multiple system configuration such as MSC– A system in which no database activity is IMS/DB


CICSIMSDL/I BATCH

VSAM DataClusters

HierarchicDatabases

Relational Databases

DB2 DL/I VSAM

Multiple Database & Transaction Managers

• Data is accessible from multiple environments


IMS CTL

TransactionManager

orDCCTL

SSM = .........

DB2 ADB2 B

( all DB2s )Application

EXEC SQL Thread

MPP

TX

LTERM

DB2 B

DRDA

DB2 A

ƒ Thread from MPP to DB2 necessary for:

1 Process SQL requests

2 Give back the results

IMS/TM Connections to DB2

• IMS Transactions can use DB2 as an External Database Manager


IMS Control Region

TransactionManager

orDCCTL

DB2 B

Attachment

SSM = .........

DB2 ADB2 B

( all DB2s )

DB2 A

ƒ Attachment from CTL to DB2 necessary for:

1 2 Phase Commit (serializing of Sync Point Processing) or Single Cycle Commit

2 Commands from IMS to DB2

IMS/TM Connections to DB2...


IMS Attachment Facility Supports …

• Connection between IMS Subsystems and one or more DB2 Subsystems

• Communication between IMS Users and DB2– Command Thread– Transaction Threads

• Application Programming Interface– DB2 Precompiler– Language Interface

• Coordinated Recovery/Restart– Unit of Work/Unit of Recovery– Two-Phase Commit Protocol– Indoubt Thread Resolution


IMS

z/OS

IRLM DB2

IMS/TM

DL/ISAS DBRC MSG IFP BMP IRLM

DL/IBATCH IRLM SSAS DBSAS

DB2LOG

DB2CATLG

DB2TABLE

BSDS DIR

IMSLOG

IMSDB (S)

RECON

z/OS Environment

• IMS and DB2 must be on same z/OS• One DB2 S/S can be connected to multiple IMSs• One IMS S/S can connect to multiple DB2s• One IMS dependent region can connect to multiple DB2s• One application program can access only one DB2 per schedule


IMS DB2-Related Commands

• Subsystem Commands:/DISPLAY SUBSYS xxxx

displays status of connections/STOP SUBSYS xxxx

disconnects DB2 from IMS/START SUBSYS xxxx

reconnects DB2 to IMS after /STOP

• Subsystem Request Command:/SSR-Display ....

DB2 Command "DISPLAY ...." sent to DB2


IMS-DB2 System Definition

• No specific IMSGEN or DB2 Installation requirements, except defining Programs and Transactions to IMS

APPLCTN PSB=PRGMA TRANSACT CODE=TRANA

• Must Define the IMS-DB2 Connections– Subsystem Member (SSM) in IMS.PROCLIB

• DB2 Pre-compiler:– Checks syntax of SQL calls– Replaces EXEC SQL with CALL DSNHLI– Creates DB Request Module (DBRM)– Includes timestamp in source and DBRM

• Compile "Modified" Source– CALL DSNHLI

• Link-Edit with IMS call interface module (DFSLI000)– Entry point is DSNHLI


z/OS

IMS/DBCTL

DBRC DLISAS

IMS BATCHBMP (S)

RECON

CORPORATEDATA

IMS BATCHBMP (S)

FPDEDB

OLDS

WADS

DL/IDB(S)

BATCHDB(S)

CICSDL/I

DB(S)

DBCTL Subsystem CICS Subsystem

APPL

APPL

DL/I

CICS User

Database Control (DBCTL) Subsystem

• CICS Transactions can use IMS as an External Database Manager


Database Control (DBCTL) Subsystem

• An IMS/DB stand-alone subsystem• Supports Full-Function databases and Fast Path DEDBs• Maximum 4095 concurrent BMP Address-spaces

– Total BMPs + CICS transaction "threads"• BMP address-spaces may contain:

– Batch programs (converted DBBBATCH/DLIBATCH)– Online Image Copy (OLIC) jobs– Fast Path DEDB utilities

• z/OS Console for operator control:– START, SHUTDOWN, RESTART of DBCTL– Connection from CICS to DBCTL

• Concurrent connections from multiple CICS subsystems


z/OS

S/S IMS DB/DC Sub-system

CICS

TRANSACTION

MANAGER

MSDB (S)

IMS/TM DLISAS DBRC

MPR(S) IFP(S)

DEDBDB(S)

DL/I

DB(S)RECONOLDS

WADS

IMS DB/DC used for DBCTL Services

• IMS DB/DC subsystem provides DBCTL Services– Connected CICS(s) have concurrent database access without Data

Sharing (IRLM not needed)– MSDBs are only known to IMS TM transactions


CONNECT

DRA

CICSCICS

PST 1

.

.

.

.

PST 4

PST 3

PST 2

PST nPST n

.

.

.

.

.

.

.

PST 4

PST 3

PST 2

IMS - CONTROL - REGION& CHECKPOINT RESTART

T h r e a d - T C B

T h r e a d - T C B

BMP

CICS / IMS Interface Structure


Two PhaseCommit

C I

C S

CICS-Syslog

CICS relatedInformation

D

B C

T

L

O L D S

DBCTL relatedInformation

Logstreams defined toz/os - Logger as - CF structure or - Dasd Datasets

CICS/DBCTL Two Phase Commit Overview


Phase 2Phase 1

Phase 2Phase 1

CICSCICS

IMSIMS

10

11

1

old point ofconsistency

4

Syncpoint

5

6

Begin ofcommit

9

Instant ofcommit

14

new point ofconsistency

3

2

DATA

aabacked

outat

restart

bbbacked

outat

restart

ccindoubt at

restart;either

backed outor

commited

ddcommitted

atrestart

Unit of RecoveryUnit of Recovery

x'5607'

Sched

x'5610'

Prepare

x'3730'

Commit

12

13

x'5612'

End Phase 2

8

7

x'5611'

End Phase 1

CICS/DBCTL Two Phase Commit Process


CICS-DBCTL Summary (1 of 2)

• Performance– Up to 999 concurrent applications

• Separate subsystems and address-spaces provide VSCR• Common logging facility over CICS journal:

– Dual logging option– User-specified number of log data sets– Automatic archiving under DBRC control– Combined logging versus separate off-line batch job logging

• 2 Phase Commit Process is needed to insure data integrity– this process is managed by CICS


CICS-DBCTL Summary (2 of 2)

• Increased data availability:– Concurrent Image Copy (CIC) of DB Datasets– DB data available after DBCTL restart

• WRITE I/O virtual buffers are logged– Backout failure: Stop only those DBs not backed-out– Successful PSB schedule even when some DBs are Not Available

• Fast Path DEDB access:– High availability (Area concept)– Potential performance benefits– Larger databases


Application using RRS

ODBA

Application using RRS

ODBA DL/I

IMS DBCTL or

IMS/DB/TMDBRC

ODBA Services

Managed by z/OS RRS

Open Database Access

• Callable Interface used to issue DL/I calls to an IMS DB subsystem


Unit Summary

• MSC (Multiple Systems Coupling) supports distributing transaction processing among many IMS subsystems

• ISC (Inter System Communications) supports distributing application flows among IMS and non-IMS subsystems (for example, CICS)

• IMS TM Transactions can access DB2 as an external Database manager

• CICS Transactions can access IMS as an external Database manager

• When IMS is accessed by CICS transactions, a 2 phase commit process is usually required for data integrity reasons– a 2 phase commit process is also used when IMS transactions

access DB2 data

Technology

IMS Fundamentals - Connecting to other Subsystems