Db2 file system
The Db2® file system supports sequential, indexed, and relative files. It provides enhanced interoperation with TXSeries® or CICS® TX, enabling batch COBOL programs to access CICS ESDS, KSDS, and RRDS files that are stored in Db2.
The implementation of the Db2 file system ensures that each COBOL operation is committed to the database so that no transactional or other database semantics show through to the COBOL program.
The Db2 database management system (DBMS) provides backup, compression, encryption, and utility functions, and also provides Db2 users with a familiar maintenance and administration protocol.
The db2
command-line
utility provides administrative functions for Db2 files. For example, you might use the db2
describe
command to print details about a file called CICS.Transaction.log in
the Db2 file system:
> db2 describe table CICS.\"Transaction.log\"
Data type Column
Column name schema Data type name Length Scale Nulls
----------------------- --------- ------------------ -------- ----- ----
RBA SYSIBM CHARACTER 8 0 No
F1 SYSIBM CHARACTER 41 0 No
F2 SYSIBM VARCHAR 29 0 No
For more information about the functions that are
provided by the db2
utility, enter the command db2
.
The Db2 file system is nonhierarchical.
- A given program can use Db2 files in only one database.
- The Db2 file system is not safe for use with multiple threads.
Interoperation with TXSeries or CICS TX:
- The schema name for the Db2 table
must be
CICS
. Specify the fully-qualified name in one of these items:- The
ASSIGN TO
literal, for example,ASSIGN TO 'CICS.MYFILE'
- The environment variable value,
for example,
export ENVAR=CICS.MYFILE
- The
ASSIGN USING
data-name value, for example,MOVE 'CICS.MYFILE' TO fileData
The rest of the file-name after the schema must be uppercase.
- The
- Fixed-length files
have the following maximum record lengths:
- Indexed (KSDS): 4005 bytes
- Relative (RRDS): 4001 bytes
- Sequential (ESDS): 4001 bytes
- Files that have record lengths that are larger than the maximum record lengths for fixed-length files must be defined as variable length.
- The maximum record length is 32,767 bytes.
- If a Db2 file is created
by a COBOL program, the runtime option
FILEMODE(SMALL)
must be in effect.
Effect of CLOSE statement on file types (COBOL for Linux on x86 Language Reference)
DB2® Database Administration Concepts and Configuration Reference (SQL limits)