Vsam file

Master catalog is used to see all the files that are controlled by it. There are lots of attributes of the files that are used like password, authentication, and authorization of the files. It also used to monitor the files to check for the space that is available and maintain the master catalog.

The attributes of the files are updated and maintained with the change in the information and keep always the current content and information. The operations that are perfomed using the file are done in a secure manner. There can be some operations like open and close that can be performed on the user's request to create the catalog more secure.

The entries in this catalog consists of all the operations of the system and management techniques. What is the main purpose of having user catalog in VSAM?

The user catalog consists of the lower hierarchy of the catalog, that contains the same structure as the master catalog. It is used to enhance the security of the user point of view and keeps all the files pointed towards the master files. The master catalog points to the user catalog that is defined and points to VSAM files. There is a possibility that user catalog can be represented in any number of instances rather than having only one instance like master catalog.

The structure of VSAM is given such that if any link is deleted it will delete the master catalog as well. The affect will only be on the master catalog and the user catalogs won't be affected. If the user catalog is destroyed the file under the catalog will also be destroyed. What is the purpose of having VSAM data space? VSAM data space is an area where the direct access to the entire volue is given.

It is possible to occupy the portion or the volume that is defined in the catalog. When the space allocation is specified then VSAM takes the full control of it. It maintains the space that is needed by the VSAm files. This files are defined using virtual tables. The master cluster or the user catalog allows new data space to be created to hold the user catalog entries.

This consists the amount of space that is required for the user catalog. Master catalog consists of the pointer to the user catalog and allow all the data set to be joined together or have a relationship between them.

The user catalog has higher level of qualifies that is same as the name of user catalog. Linear dataset consists of byte-addressable strings that are used in the virtual storage.

VSAM dataset is used to have control interval of the size bytes. There are no boundaries i. The embdded control information is not looked in the logical records that can be locked or unlocked for the application program. The program that don't exist are from VSAM. The linear dataset consists of data component only. It is used to store the data set in linear fashion that allows the record to be submitted before taking a copy of it. VRRDS variable relative record data set : is used as an alternative index that is provided with the base cluster.

It uses an alternate key in each record. It uses an unique key that is always take the alternate keys. The base cluster can also consists of many alternate indexes. The path that is defined in this uses an alternate index for the data set that has to be inserted. This cluster is having the paths opened to provide the access to all the dataset that are present with different logical keys. The alternate index can be processed as a dataset without using any other mechanism just by using the component of a path.

There are few upgrade set that are used to set the base cluster for the alternate indexes and it need to be updated everytime there is a change in the data set. How does control Intervals and control Areas related to each other? The control interval is the basic unit of information that is used by VSAM.

It resides between the main storage and peripheral storage to provide easy access to the data set. It has a defined set that is been given by the system and all the datasets are also of the same size so that it will be easier to use it and implement it.

The size of the control interval is in between and 32, bytes and it always comes in multiple of , or of It is always necessary to keep the size higher due to the control interval size which can be greater than track size. The control areas consists of logical records, unused space, and control information that is provided for the reusability and to implement the correct record size. What are the access method services used in VSAM? There are many utility programs that are used to create and maintain the VSAM catalogs.

This catalog consists of data spaces that is required by all the data sets and use of data sets to provide the storage container for the data arriving. IDCAMS is used just for this purpose to handle the request of the user and provide simple commands to keep the association with other parameters.

Access method services allow easy to access services without doing hard core programming and easy to use interface so that user can fill the data and use many dataset functions. What are the steps involved in access method services? Calling of IDCAMS from some other computer using the compatible program so that the integrated functionality can be activated that helps in maintaining different catalog facility catalogs.

What are the different parameters that are used in VSAM? There are different parameters that are used to provide VSAM services like:Positional parameters that are required to be coded to be used as a pre-defined sequence that allow many parameters to be used and managed for which the position is changing. The appearance should be visible for all the parameters that are coming before any keyword.

Keyword parameter is prefixed by a keyword that defines the meaning of any parameter that is used. It can be coded in a particular sequence by seeing all the positional parameters. It has a particular form of a list that uses all the subparameters as well. Sub-parameter: is always contained inside a parameter and used only when it is required. The sub-parameters use separators to separate themselves from the actual parameters. Why is it required to have a Keyed directed retrieval?

Key sequenced data sets provide the use of both sequential and direct processing of the data sets by the use of a unique key. The direct processing require to supply VSAM with the defined key that allows the record to be accesed. The keys can be used to access indirectly but it should be of the same length as the keys that are given in the data set. The key should exist in the data set. There is given a program through which the records can be accessed directly. The user can enter the records from the terminal and the program displays the record on the screen.

How is the sorting of VSAM files carried? We can access the records directly and for safety purpose we can use passwords also. The following syntax shows which parameters we can use while creating ESDS cluster. Above syntax shows which parameters we can use while deleting ESDS cluster.

Index component refers the physical address of a KSDS record. This relates the key of each record to the record's relative location in the data set. When a record is added or deleted, this index is updated accordingly. Each record in the data component of a KSDS cluster contains a key field with same number of characters and occur in the same relative position in each record.

Records within KSDS data set are always kept sorted by key-field. Records are stored in ascending, collating sequence by key.

Records are identified using a key. The key of each record is a field in a predefined position within the record. Each key must be unique in KSDS dataset. So duplication of records is not possible. When new records are inserted, the logical order of the records depends on the collating sequence of the key field. In order to search for a particular record, we give a unique key value.

Key value is searched in the index component. Once key is found the corresponding memory address which refers to the data component is retrieved. From the memory address we can fetch the actual data which is stored in the data component. Above syntax shows which parameters we can use while deleting KSDS cluster. A Relative record dataset has records that are identified by the Relative Record Number RRN , which is the sequence number relative to the first record.

RRDS allows access of records by number like record 1, record 2, and so on. This provides random access and assumes the application program has a way to get the desired record numbers. The records in an RRDS dataset can be accessed sequentially, in relative record number order, or directly, by supplying the relative record number of the desired record. The records in a RRDS dataset are stored in fixed length slots. Each record is referenced by the number of its slot, number can vary from 1 to the maximum number of records in the dataset.

Applications which use fixed-length records or a record number with contextual meaning that can use RRDS datasets. Space is divided into fixed length slots in RRDS file structure. A slot can be either completely vacant or completely full.

Thus, new records can be added to empty slots and existing records can be deleted from slots which are filled. We can access any record directly by giving Relative Record Number. Above syntax shows which parameters we can use while deleting RRDS cluster. Linear dataset is the only form of byte-stream dataset which is used in used in traditional operating system files.

Linear datasets are rarely used. The following syntax shows which parameters we can use while creating LDS cluster. Above syntax shows which parameters we can use while deleting LDS cluster. Above syntax shows which parameters we can alter in an existing VSAM cluster. It is also used to copy data from one VSAM data set to another. We can use this command to copy data from sequential file to VSAM file. In the above syntax, the in-ddname is DD name for the Input Dataset which is having records.

The out-ddname is the DD name for the Output Dataset, where the input datasets records will be copied. In the above syntax, vsam-file-name is the VSAM dataset name for which we need all the information. ALL keyword is specified to get all catalog details.

Examine command is used to check the structural integrity of a key-sequenced data set cluster. It checks for index and data components and if any problem is found, the error messages are sent spool.

You can check any of the IDCxxxxx messages. Verify command is used to check and fix VSAM files which have not been closed properly after an error. The command adds correct End-Of-Data records to the file. In the above syntax, vsam-file-name is the VSAM dataset name for which we need to check the errors. An alternate index provides access to records by using more than one key. The key of alternate index can be a non-unique key, it can have duplicates.

Above syntax shows the parameters which are used while defining Alternate Index. Define AIX command is used to define Alternate Index and specify parameter attributes for its components. Define Path is used to relate the alternate index to the base cluster. While defining path we specify the name of the path and the alternate index to which this path is related.

Above syntax has two parameters. Catalog maintains the unit and volume where dataset resides. Catalog is used for retrieval of datasets. Master catalog is itself a file which monitors and manages operations of VSAM. Their is only one master catalog in any system which contains entries about system datasets and VSAM datasets. The master catalog is created during system generation process and resides on system volume.

Master catalog owns all VSAM resources in operating system. All files used in VSAM are controlled by master catalog. When any of the above file attributes changes they are automatically updated in master catalog. User catalog has same structure and concepts as the master catalog.

It is present at next hierarchy level after master catalog. User catalog is not mandatory in the system but it is used to enhance security of VSAM system. Master catalog points to VSAM files but if User catalog is present then master catalog points to user catalog.