I often find myself needing to search through tape catalogs to locate specific libraries or datasets, and manually reviewing DSPTAP spool files for each tape becomes tedious very quickly. So I decided to wrap the DSPTAP command in a SQL table function to make batch searches possible.
In IBM i environments, the traditional workflow for searching tape contents involves:
- Running `DSPTAP` for each tape volume
- Reviewing the resulting spool file
- Manually noting which tapes contain the desired library
- Repeating for the next tape
This process is time-consuming and error-prone, especially when you need to search across dozens of tapes to find where a specific library was saved.
So, I created a User-Defined Table Function (UDTF) that executes the `DSPTAP` command and returns the results as a SQL result set. This allows you to query tape contents using standard SQL, making batch searches and filtering much easier. Here’s the function signature:
CREATE FUNCTION SQLTOOLS.DISPLAY_TAPE (INDEV VARCHAR(10), INTAPE CHAR(6), INSEQ_START VARCHAR(10) DEFAULT '*FIRST', INSEQ_END VARCHAR(10) DEFAULT '*LAST')
RETURNS TABLE (TAPE CHAR(6), SEQUENCE_LABEL VARCHAR(17), SEQUENCE_NUMBER INTEGER, BLOCKS INTEGER, WRITE_DATE VARCHAR(10), EXP_DATE VARCHAR(10))
Now you can search for a library across multiple tapes with simple SQL:
SELECT * FROM TABLE(SQLTOOLS.DISPLAY_TAPE('TAP01', 'VOL001')) WHERE SEQUENCE_LABEL LIKE '%MYLIB%';
One of the most critical aspects of this implementation is the call to `QSYS2.END_IDLE_SQE_THREADS()` at the beginning of the function. This call is essential due to a fundamental limitation of the IBM i tape management system. The `QSYSTAP` file, which underlies all tape operations including `DSPTAP`, cannot be opened by multi-threaded processes. The DB2 for i SQL Query Engine (SQE) typically maintains a pool of idle threads for performance optimization. However, these threads would cause the `DSPTAP` command to fail when attempting to access tape resources, as the tape subsystem requires single-threaded access. By calling `END_IDLE_SQE_THREADS()`, we force the database engine to terminate any idle SQE threads before executing the tape command. This ensures that the `DSPTAP` operation runs in a single-threaded context, allowing it to successfully open and read from the `QSYSTAP` file. Without this call, the function would fail with file access.
The function is declared with `NOT FENCED`, which means it runs in the same thread as the invoking SQL statement rather than in a separate thread. According to IBM documentation, FENCED functions run in a separate thread, while NOT FENCED functions may run in the same thread as the invoking SQL statement.I As we discussed earlier, the `QSYSTAP` file used by tape operations doesn’t support multi-threaded access. Since we’re already forcing single-threaded execution with `END_IDLE_SQE_THREADS()`, using `FENCED` (which would create a separate thread) would be counterproductive and could potentially cause issues. By using `NOT FENCED`, we ensure the function runs in the same single-threaded context where we’ve already terminated the idle SQE threads, maintaining compatibility with the tape subsystem’s threading limitations.
The function dynamically bulds the `DSPTAP` command with the provided parameters:
VALUES 'QSYS/DSPTAP DEV(' CONCAT TRIM(INDEV) CONCAT ') VOL(' CONCAT TRIM(INTAPE) CONCAT ') SEQNBR(' CONCAT TRIM(INSEQ_START) CONCAT ' ' CONCAT TRIM(INSEQ_END) CONCAT ') DATA(*LABELS) OUTPUT(*OUTFILE) ENDOPT(*UNLOAD) OUTFILE(QTEMP/DSPTAP) OUTMBR(*FIRST *REPLACE)' INTO CMD;
The command is executed using `QSYS2.QCMDEXC()`, which returns a result code. If successful (THERESULT = 1), the function queries the output file created in QTEMP and transforms the raw tape label data into a structured result set.
This UDTF demonstrates how SQL table functions can modernize traditional IBM i operations by wrapping CL commands in a SQL interface. The careful handling of multi-threading constraints through `END_IDLE_SQE_THREADS()` and the use of `NOT FENCED` to maintain single-threaded execution show the importance of understanding both the database engine and the underlying system architecture.
The result is a powerful tool that transforms a manual, time-consuming process into an automated, SQL-queryable operation, enabling better tape library management and faster data location workflows.
Here the link of the code
And you, have you ever needed to search through tape catalogs programmatically? How did you solve it?
Andrea