大型机技术之VASM篇

Virtual Storage Access Method (VSAM)

Q1)What are the types of VSAM datasets?
A1)Entry sequenced datasets (ESDS), key sequenced datasets (KSDS) and relative record dataset (RRDS).

Q2)How are records stored in an ESDS, entry sequenced dataset?
A5)They are stored without respect to the contents of the records and in the order in which they are included in the file.

Q3)What is a CI, control interval?(文章来源：http://www.newcoin.info)
A3)A control interval is the unit of information that VSAM transfers between virtual and auxiliary storage.

Q4)What are the distinctive features of a ksds, key sequenced dataset?
A4)The index and the distributed free space.

Q5)What is a CA, control area?
A5)A group of control intervals makes up a control area.

Q6)What is a sequence set?
A6)This is the part of the index that points to the CA and CI of the record being accessed.

Q7)What is the index set?
A7)This is the other part of the index. It has multiple levels with pointers that ultimately reach to the sequence set.

Q8)What is a cluster?
A8)A cluster is the combination of the index, sequence set and data portions of the dataset. The operating system gives program access to the cluster, ie. to all parts of the dataset simultaneously.

Q9)What is the catalog?
Q9)The catalog contains the names of all datasets, VSAM and non-VSAM. It is used to access these datasets.

Q10)What is an alternate index?
Q10)An AIX is a file that allows access to a VSAM dataset by a key other than the primary one.

Q11)What is a path?
Q11)A path is a file that allows you to access a file by alternate index – the path provides an association between the AIX and the base cluster.

Q12)What is the upgrade set?
Q12)The upgrade set is the list of all AIXes that VSAM must maintain for a specific base cluster, so that when data in the base cluster is updated, the AIX files are also updated.

Q13)What is free space?
Q13)Free space is reserved within the data component of a KSDS to accommodate inserting new records.

Q14)What is a VSAM split?
Q14)If there isn’t enough space in the control interval VSAM performs a control interval split by moving some records to the free control intervals. If there isn’t a free control interval VSAM performs a control area split by allocating a new control area and moving half of the control intervals to it.

Q15)What is the base cluster?
Q15)The base cluster consists of the data component and the index component for the primary index of a KSDS.

Q16)Do primary key values have to be unique? Do alternate key values have to be unique?
Q16)Primary key values must be unique; alternate key values need not be.

Q17)In the COBOL SELECT statement what is the ORGANIZATION for a KSDS?
Q17)The ORGANIZATION is INDEXED.

Q18)In the COBOL SELECT statement for a KSDS what are the three possibilities for ACCESS?
Q18)ACCESS can be SEQUENTIAL, RANDOM or DYNAMIC.

Q19)What is the COBOL RECORD KEY clause?
Q19)The RECORD KEY in the SELECT clause identifies the files primary key as it will be known to the program.

Q20)What is the purpose of the FILE STATUS clause in the SELECT statement?
Q20)The FILE STATUS field identifies the field that VSAM uses to provide information about each I/O operation for the file.

Q21)If you wish to use the REWRITE command haw must the VSAM file be opened?
Q21)It must be opened as I/O.

Q22)Explain the meaning and syntax for the START command.
Q22)The START command is used read other than the next VSAM record. A value must be moved into the RECORD KEY. The KEY clause is optional, but it can be used to specify a relational (equal, less than, etc.) operator.

Q23)What is the meaning of dynamic processing?
Q23)It’s rarely used. It means one program uses both sequential and random processing for a VSAM KSDS file.

Q24)Name some common VSAM error conditions and codes.
Q24)They are end of file (10), duplicate key (22), record not found (23), VSAM logic error (90), open problem (92) and space problem (93).

Q25)What is the VSAM-code field?
Q25)It is a COBOL II enhancement to VSAM batch processing expanding the FILE STATUS field. It is defined in WORKING-STORAGE as a six byte group item with three two byte elements, the normal return code, the function code and the feedback code.

Q26)What is a VSAM slot?
Q26)A relative record dataset (RRDS) consists of a specified number of areas called slots. Each slot is identified by a relative record number (RRN) which indicates its relative position in the file.

Q27)What is the utility program closely associated with VSAM?
Q27)IDCAMS, the access method services utility.

Q28)There are at least seven IDCAMS commands; name and explain each of them ?.
Q28)ALTER modifies information for a catalog, alternate index, cluster or path. BLDINDEX builds the alternate index, of course. DEFINE is used for ALTERNATEINDEX, CLUSTER or PATH. DELETE removes the catalog entry for a catalog, cluster, alternate index or path. LISTCAT lists information about the dataset. PRINT prints the dataset contents. REPRO copies records from one file to another.

Q29)What are the three levels of definition for the VSAM DEFINE?
Q29)They are DEFINE CLUSTER, DATA and INDEX.(文章来源：http://www.newcoin.info)

Q30)What is the significance of the SHAREOPTIONS parameter?
Q30)It specifies how the file may be shared between jobs and between batch and CICS environments.