How many extents are possible for a vsam file

An HFS data set can have extents on each volume. Posted: Thu Oct 12, am. But keep in mind that an extent is not always equal to the primary or 2ndary values specified in the DD card for the dataset. A primary alloc may take up to 5 extents to be satisfied. That will leave only 10 extents to satisfy your 2ndary allocs. The 2ndary allocs may take up to 3 extents to satisfy each alloc.

So that means you may get as little as 3 2ndary allocs. If it can't, it takes what it can get contiguously then uses another extent for the remaining space, if it can't get enough contiguously, it tries again until it uses all the extents and View previous topic :: :: View next topic.

Similar Topics. The file status key is divided. It has unstructured 4k bytes fixed size CIs which do not contain control fields and therefore from VSAM's standpoint they do not contain any logical records. There is no free space, and no access from Cobol. LDS is essentially a table of data maintained on disk. The 'table entries' must be created via a user program and can only be logically accessed via a user program.

When passed, the entire LDS must be mapped into storage, and then data is accessed via base and displacement type processing. A cond code of 4 indicates a warning. What will be the condition code returned to the operating system? Must be between bytes to 32 k. Usually either 2K or 4K. A larger control interval increases performance for sequential processing while the reverse is true for random.

Control Area is a group of control intervals. CA is used during allocation. Q40 CI size should be based on record length, type of processing. Usually CI is 4K. Usual values are 20 20 when heavy updates are expected.

CI size can be calculated. Q41 No. Because you cannot insert records in an ESDS, also when you rewrite a record, it must be of the same length. Thus putting any value for freespace does not make any sense.

It is coded as SHAREOPTS a b , where a is the cross region share option ie how two or more jobs on a single system can share the file, while b is the cross system share option ie how two or more jobs on different MVSs can share the file. Usual value is 2 3. Q43 Value of 2 for cross region means that the file can be processed simultaneously by multiple users provided only one of them is an updater.

Value of 3 for cross system means that any number of jobs can process the file for input or output VSAM does nothing to ensure integrity.

To read using the alternate index, use the dd name of the path in CICS file control commands. Attempting to open for input will fail.

An empty file can be opened for output only. Q49 Can write a dummy program that just opens the file for output and then closes it. Q50 Duplicate alternate key. Happens on both input and output operation Q51 How do you calculate record size of an alternate cluster?

Give your values for both unique and nonunique. Q54 How do you define a GDG? This dataset is known as the model dataset. Q55 No, the DCB of the model dataset can be overridden when you allocate new versions. Q56 How are different versions of GDG named? Q56 base-file-name. Q57 Suppose 3 generations of a GDG exist. How would you reference the 1st generation in the JCL? Q58 Suppose a generation of GDG gets created in a particular step of a proc.

How would you refer the current generation in a subsequent step? What would be the disposition of this generation now? What do you do? Q63 Out of space condition is raised. Q65 - but you must be a nut to have so many ALT Indexes on a dataset! Q66 Yes.

Because the alternate key would first locate the primary key, which in turn. Recovery preformats the control areas during the initial dataset load, if the job fails, you can restart but you must have a recovery routine already written to restart the job.

Q68 It defines the cross-region and cross-system sharing capabilities of the dataset. A69 It divides a large dataset into several volumes according to the Key ranges specified. Q70 What are the optional parameters to the input dataset While loading the empty cluster with the data records?

Q72 How to delete a member using JCL. ESDS maintains control information. But LDS does not maintains the control information. Is rewrite operation possible in ESDS? Yes rewrite operation is possible in an ESDS. Q75 What is an alternate index and path? A75 An alternate index is an another way of accessing key sequenced data record stored in a base cluster and path is the linkage which connect alternate index to its base cluster.

A76 2 data buffers by default for ESDS. For KSDS it allots 2 data buffers and 1 index buffers. Q77 what's the biggest disadvantage of using a VSAM dataset? Q79 How many times secondary space allocated? A80 The answer is : 1 Q81 what is a Base Cluster?

A82 No, they would not be left empty. A logical record is a unit of information used to store data in a VSAM data set. The minimum size of a CI is bytes. The maximum size of a CI is 32K. In a CI if two or more adjacent records have the same length, only two RDfs are used. The minimum size of a CA is 1 track. The maximum size of a CA is 1 cylinder.

LDS has no imbedded control information in its CI. LDS has only a data component. LDS cannot have an alternate index. RRDS consists of a number of preformatted fixed-length slots.

RRDS has only a data component. For an RRDS the relative record number is used as a search argument. RRDS supports only fixed length records. ESDS has only a data component.

Spanned records must be accessed in MOVE mode. The 4Gig limit applies to space allocated, so if you have 2. With EA, the 4G architectural limit for data set size imposed by using the 4-byte field for the relative byte address RBA was eliminated. A 4K CI size is preferred by many applications for performance reasons.

No increase in processing time is expected for extended format data sets that grow beyond 4 GB. To use EA, the data set must be:.

The lack of this additional space is perceived by:. No extent in the current volume contains a specific searched RBA. Then, EOV acquires new extents interfacing with DADSM, updates the VSAM control block structure for the data set with the new extent information, and updates the critical control block data in common storage and in the catalog, so that this new space is accessible by all regions using this VSAM data set.