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VSAM INFORMATIONINFORMATION TAKEN FROM: VSAM ACCESS METHOD SERVICES AND PROGRAMMING TECHNIQUES, BY JAMES MARTIN..... VSAM - VERY POPULAR ACCESS METHOD .. INTRODUCED BY IBM IN THE 1970S ALONG WITH THE IBM SERIES 370 MACHINES... REPLACED OLDER ACCESS METHODS (ISAM, BDAM, AND VIRTUAL COUNTERPARTS.).. IS THE UNDERLYING DATA MANAGEMENT ACCESS METHOD THAT MOST HIGH PERFORMANCE DATA BASE SYSTEMS FOR IBM USE... A THOROUGH KNOWLEDGE OF VSAM IS REQUIRED. .. WIDELY USED FOR MANY FORMS OF FILE ACCESS .. MOST MAINFRAME IBM USERS STILL USE VSAM... YOUR KNOWLEDGE OF VSAM WILL SUPPORT YOUR STUDIES IN DATABASE PROCESSING AND ALL DIRECT FILE ACCESSING USING IBM MAINFRAMES....1VSAM DATA SET STRUCTURE:. VSAM DATA SET IS OFTEN CALLED A "CLUSTER." . A KSDS CLUSTER CONSISTS OF A .. DATA COMPONENT OF CONTROL INTERVALS CONTAINING RECORDS, FREE SPACE, CONTROL INFORMATION,.. INDEX COMPONENT USED TO LOCATE RECORDS.. ESDS & RRDS CONSISTS OF DATA COMPONENT ONLY... KSDS = KEY SEQUENCED DATA SET(INDEXED FILE).. RRDS = RELATIVE RECORD DATA SET (RELATIVE I/O).. ESDS = ENTRY SEQUENCED DATA SET (SEQUENTIAL FILE). VSAM KSDS FACILITY PROVIDES THE WIDEST RANGE OF FEATURES AND CAPABILITIES, AND KSDS CLUSTERS ARE MORE WIDELY USED THAN EITHER DSDS OR RRDS CLUSTERS.. WILL DISCUSS RRDS CLUSTERS LATER2ACCESS METHOD SERVICES (AMS). SUPPLIED WITH VSAM. IS A GENERAL-PURPOSE UTILITY PROGRAM . USED for WIDE RANGE OF FUNCTIONS TO SUPPORT VSAM DATA SETS AND THEIR APPLICATIONS.SUCH FUNCTIONS INCLUDE: 1. DEFINING, ALTERING, AND DELETING VSAM DATA SETS2. LISTING AND MAINTAINING VSAM CATALOG ENTRIES3. LOADING, COPYING, AND PRINTING VSAM DATA SETS4. CONSTRUCTING ALTERNATE INDEXES5. RECOVERING FROM VARIOUS TYPES OF ERRORS 6. PORTING DATA SETS BETWEEN OPERATING SYSTEMSTHE JCL SUPPORTING VSAM ACTIVITIES IS COMPLEX.VSAM TRIES TO SIMPLIFY THE JCL AND CREATES MANY OF THE SUPPORT UNDERLYING DATA STRUCTURES (LIKE CATALOGS, INDEXES, AS NEEDED FOR VSAM) AS WELL AS PROVIDING SEVERAL UTILITY PROGRAMS THAT ARE DESIGNED TO ACCESS VSAM FILES, SUCH AS VSAM PRINT, VSAM REPRO, AND MORE.BUT, IN ORDER FOR VSAM TO DO THESE THINGS FOR YOU, YOU MUST SET UP YOUR OWN VSAM ENVIRONMENT, WHICH INCLUDES FORMATTING YOUR OWN ADISK@ IN A MANNER THAT IS ACCESSIBLE BY THE SERVICES PROVIDED BY VSAM.YOU MUST THEN DEFINE YOUR MASTER CATALOG, SO VSAM CAN FIND YOUR FILES.YOU MUST ALLOCATE THE PHYSICAL SPACE ON DISK FOR YOUR CLUSTER (DATA PORTION AND INDEX PORTION).3YOU MUST NAME THESE FILES AND REQUEST A CERTAIN AMOUNT OF DISK SPACE.YOU MUST TELL THE VSAM UTILITIES (THAT DEFINE YOUR CLUSTER FOR YOU) YOUR RECORD SIZE, HOW MANY TRACKS OF DISK TO ALLOCATE FOR YOUR FILE, THE LOCATION AND SIZE OF YOUR RECORD KEY, THE NAMES OF YOUR DATA AND INDEX FILES, AND MORE.GIVEN THAT YOU HAVE A CATALOG, HAVE ALLOCATED SPACE, HAVE DESCRIBED SEVERAL OF YOUR RECORD AND FILE PARAMETERS, THEN, UPON REQUEST, VSAM CAN CREATE A VSAM FILE DIRECTLY FOR YOU FROM YOUR SORTED SEQUENTIAL FILE. (YOU MAY CREATE YOUR OWN FILE VERY EASILY TOO WITHOUT THE VSAM REPRO BY SIMPLY CREATING THE FILE (AFTER SPACE, ...., HAS BEEN NAMED) VIA A COBOL PROGRAM. REMEMBER: ACCESS IS SEQUENTIAL, OPEN FOR OUTPUT, ORG IS INDEXED, RECORD KEY IS WHATEVER....(AND ALTERNATE KEYS SPECIFIED, IF ANY).ONCE THIS FILE IS CREATED, YOU ARE ON YOUR WAY WITH THE COBOL INSTRUCTIONS AND TECHNIQUES DISCUSSED IN CLASS AND IN YOUR TEXTBOOK.BUT, IN ITS INFINITE KINDNESS, VSAM ALSO GIVES YOU MANY UTILITIES THAT YOU MAY USE AS NEEDED.A FEW INCLUDE:A PRINT FACILITY, A DELETE FACILITY, A LIST CATALOG FACILITY, A VERIFY FACILITY, AND OTHERS.VSAM STORAGE STRUCTURES. KSDS HAS AN INDEX COMPONENT AND A DATA COMPONENT4. PHYSICAL I/Os DONE WITH BLOCKS IN CONVENTIONAL ACCESS METHODS. IN VSAM, PHYSICAL I/O DONE IN CONTROL INVERVALS.. A CONTROL INTERVAL CONTAINS1. RECORDS2. CONTROL INFORMATION (record descriptors)3. FREE SPACE (FOR EXPANSION)REC 1REC 2REC 3REC 4FREE SPACECTLINFOCONTROL INTERVALAT LOAD TIME:CONTROL INTERVALS ARE CREATED RECORDS WRITTEN INTO THEM.CONTROL INTERVALS GROUPED INTO CONTROL AREAS.CONSIDER THE FOLLOWING DRAWING: 5INDEX COMPONENT …. . .INDEX SETSEQUENCE SET CONTROLINTERVALSCONTROL AREACONTROL AREACONTROL AREA. . . DATA COMPONENT6. THE INDEX IS USED TO LOCATE RECORDS IN THE DATA COMPONENT.. INDEX COMPONENT CONSISTS OF:.. INDEX SET AND.. SEQUENCE SETS. ONE SEQUENCE SET IS NEEDED FOR EACH CONTROL AREA. ONE ENTRY WITHIN EACH SEQUENCE SET FOR EACH CONTROL INTERVAL WITHIN THAT CONTROL AREA.. THE RECORDS IN EACH CONTROL INTERVAL ARE MAINTAINED IN PHYSICAL SEQUENCE BY KEY VALUE, AND SEQUENCE SET ENTRIES MAINTAIN THE LOGICAL SEQUENCE OF THE CONTROL INTERVALS WITHIN EACH CONTROL AREA.. CONTROL INTERVALS IN A CONTROL AREA ARE NOT NECESSARILY IN PHYSICAL SEQUENCE ACCORDING TO THE KEY VALUES OF THE RECORDS CONTAINED IN THEM. THE SEQUENCE SETS ORDER THE CONTROL INTERVALS WITHIN CONTROL AREAS.. IF THERE IS MORE THAN ONE CONTROL AREA, THEN THERE IS AN INDEX SET IN ADDITION TO THE SEQUENCE SETS.. AN ENTRY IN THE INDEX SET POINTS TO EACH SEQUENCE SET. SO ONCE THERE IS MORE THAN ONE CONTROL AREA, THERE IS MORE THAN ONE SEQUENCE SET. . THUS WE HAVE THE INDEX SET TO MANAGE THE SEQUENCE SETS.. THUS TO ACCESS RECORDS, WE HAVE A TREE STRUCTURE, INDEX SET => SEQUENCE SET => CONTROL INTERVAL (TWO LEVELS OF INDICES) THIS HIERARCHY GENERALIZES....CAN HAVE MULTIPLE INDEX SETS FOR EXTREMELY LARGE KSDSs.7PLEASE NOTE (TO KEEP THINGS IN PERSPECTIVE) THAT KSDS CONTROL AREAS ARE QUITE LARGE AND MAY CONTAIN THOUSANDSOF RECORDS.A KSDS WOULD HAVE TO BE VERY LARGE TO REQUIRE TWO LEVELSOF INDEX SET RECORDS AND WOULD HAVE TO CONTAIN LITERALLY MILLIONS OF RECORDS BEFORE THREE LEVELS OF INDEX SET RECORDS WOULD BE REQUIRED.MORE NOTES:. ONE SEQUENCE SET PER CONTROL AREA. SEQUENCE SET ENTRY POINTS TO HIGHEST RECORD IN CONTROL INTERVAL. FREE SPACE IN CONTROL INTERVALS (FOR DATA AND SEQUENCE SETS TOO.). CAN ALSO HAVE FREE CONTROL INTERVALS IN A CONTROL AREA (FOR GROWTH AND CONTROL INTERVAL SPLITTING)THINK: (WHILE NOT ABSOLUTELY TRUE, THIS MAY HELP...)CONTROL INTERVALS: RECORDS IN BLOCK OR TRACKCONTROL AREAS: TRACKS (NOT NECESSARILY CONTIGUOUS)IN A CYLINDER. . CONTROLLED/ACCESSED BY SEQUENCE SETSINDEX SETS: POINT TO DIFFERENT CYLINDERS.... CONSIDER THE EXERCISE FOR THE NEXT DRAWING....8I1 I2S1 S2 S3D1 D2 D3 D49/S162S2FREEFREEFREEFREEFREE


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UNF COP 3531 - VSAM Information

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