How does COBOL read VSAM randomly?
COBOL VSAM Files READ with START Logic
- Establish a Key. START statement positions the cursor.
- READ Statement. The purpose of READ statement is to fetch a record randomly after establishing a key.
- READ NEXT Statement. READ Next fetches records sequentially till end of the input VSAM file.
- Write a Record.
What are the different access modes for a VSAM file?
You can access records in VSAM indexed and relative files in three ways: sequentially, randomly, or dynamically. For sequential access, code ACCESS IS SEQUENTIAL in the FILE-CONTROL entry. Records in indexed files are then accessed in the order of the key field selected (either primary or alternate).
What is difference between dynamic and random access in COBOL?
random access mean you randomly locate the record using RBA for ESDS , RRN for RRDS and Primary key for KSDS and your search goes record by record. dynamic access means you dynamically locate a record and from there you perform sequential operation.
What is random access in COBOL?
Random Access For indexed files, records are accessed according to the value placed in a key field which can be primary or alternate key. There can be one or more alternate indexes. For relative files , records are retrieved through relative record keys.
When you read a VSAM file randomly if the record is not found what is the status code you will get?
file status 23 The record is not found when you are trying to access using a key. File not found.
What is access mode?
Definition. Access mode is. [a] distinct operation recognized by the protection mechanisms as a possible operation on an object. Read, write and append are possible modes of access to a file, while execute is an additional mode of access to a program.
What is access mode of a file?
The access mode is used to define the accessing way of the file based on the requirements in the program. In short, we can say, access mode defines how the data is required to read and write from the file. Mainly there are three access modes: Sequential Access. Random Access.
What is dynamic access mode?
Allows a specific input-output request to determine the access mode. Therefore, records may be processed sequentially and/or randomly. Parent topic: Access Modes.
What is the meaning of dynamic processing in VSAM?
Dynamic access is a mixed sequential-random access in the same program. Using dynamic access, you can write one program to perform both sequential and random processing, accessing some records in sequential order and others by their keys. Example: using dynamic access with VSAM files.
Can we access the VSAM file only with the alternative index?
Normally a VSAM file is accessed via Primary key. This primary key cannot have duplicate values. In practical applications, one would need to access the VSAM file by way of fields other than the primary key also. In such cases, Alternate index is used for accessing a VSAM file.
How do you verify a command in VSAM?
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.
What is the difference between trunk mode and access mode?
Both Fast Ethernet and Gigabit Ethernet ports can be set to access or trunk mode. By default, a port is in access mode and carries traffic only for the VLAN to which it is assigned. In trunk mode, a port can carry traffic for multiple VLANs.
What is the use of access mode?
The access mode is used to define the accessing way of the file based on the requirements in the program. In short, we can say, access mode defines how the data is required to read and write from the file. Mainly there are three access modes: Sequential Access.
What is the default file access mode?
access_mode − The access_mode determines the mode in which the file has to be opened, i.e., read, write, append, etc. A complete list of possible values is given below in the table. This is optional parameter and the default file access mode is read (r).
What is access mode for start statement in COBOL?
The START statement provides a means of positioning within an indexed or relative file for subsequent sequential record retrieval. When the START statement is executed, the associated indexed or relative file must be open in either INPUT or I-O mode.
What is repro replace in VSAM?
When using REPRO, the REPLACE parameter lets you merge a backup copy into the damaged data set. You cannot use the REPLACE parameter with entry-sequenced data sets, because records are always added to the end of an entry-sequenced data set.
What is control interval in VSAM?
Control Intervals (CI) in VSAM are equivalent to blocks for non-VSAM data sets. In non-VSAM methods, the unit of data is defined by the block. VSAM works with logical data area which is known as Control Intervals. Control Intervals are the smallest unit of transfer between a disk and the operating system.