File statistics and tuning
Overview
Model 204 maintains a variety of utilization statistics for each user and file active during a particular run. These statistics are written to the journal, as explained in the Rocket Model 204 System Manager's Guide, which also provides a complete description of all Model 204 statistics.
Even if not users of the products, the manuals for the real time monitor SIRMON and SIRTUNE provide useful advice on monitoring and tuning Model 204 files (as well as program and system performance as a whole).
For more information on using journals in system and media recovery, see Producing and archiving journals.
When file statistics are printed
File statistics are kept for every file opened during the run. These statistics summarize the activity on the file for all users. File statistics normally are written to the journal when the file is closed in lines that, when printed, start with:
ST $$$ FILE='filename'
Only those statistics whose value is not zero are printed.
File statistics might not appear for every CLOSE command issued. When many users are working with one file, the file is kept open until the last user issues a CLOSE command. The statistics appear along with the last CLOSE. System termination prints file statistics for each file still open at the end of the run.
File statistics summary
| Term | Number of... |
|---|---|
| BADD | Fields added to Table B |
| BCHG | Fields changed in place in Table B |
| BDEL | Fields deleted from Table B |
| BXCHNG | Changes to Ordered Index B-Tree entry length |
| BXDELE | Deletions of Ordered Index B-Tree attribute-value pair entries |
| BXNEXT | Lateral moves in an Ordered Index B-Tree entry range search |
| BXFIND | Finds of Ordered Index B-Tree attribute-value pair entries |
| BXINSE | Inserts of new Ordered Index B-Tree attribute-value pair entries |
| BXSPLI | Ordered Index B-Tree node splits, all levels |
| BXRFND | Ordered Index B-Tree refinds |
| BXFREE | Ordered Index B-Tree nodes emptied and freed |
| DIRRCD | Table B records searched |
| DKRD | Disk reads from the file |
| DKWR | Disk writes to the file |
| DUPDTS | Records written to the deferred update data sets for the file |
| DKUPTIME |
Milliseconds of elapsed clock time that it has taken Model 204 to write a file's pages to disk and to mark it "physically consistent" on disk. Includes all time spent writing pages, even if disk updates are interrupted, as indicated by the message: M204.0440: FILE filename DISK UPDATE ABORTED |
| IXADD | Index entries added to Tables C and D, including attempts to add duplicates |
| IXDEL | Index entries deleted from Tables C and D |
| PNDGTIME | Milliseconds of elapsed clock time that a file waited to be written to disk, after the last update unit completed |
| RECADD | Records, not including extension records, started in Table B |
| RECDEL | Records, not including extension records, deleted from Table B (does not include records deleted by DELETE RECORDS or IFDSET) |
| REQ | Requests and DISPLAY commands run on the file |
| RETRYA | Page retries in Table A |
| RETRYC | Page retries in Table C |
| UPDTTIME | Milliseconds of elapsed clock time that an open file has been part of at least one update unit |
Monitoring field retrievals in FIND statements
If you have defined a field as NON-KEY, NON-ORDERED, and NON-RANGE, you can monitor the use of the field in FIND statements using information written to the journal data set and redefine it as KEY, NUMERIC RANGE, or ORDERED when necessary.
Whenever such a field is used in a retrieval, an MS line is written to the journal with the message:
*** M204.0179: TABLE B SEARCH IMPLIED FOR FIELD = fieldname
This message indicates that a direct search of the data set might be required. It does not indicate whether the search was actually performed or how many records were searched (which depends on the results of any inverted conditions in the FIND statement).
The DIRRCD statistic provides a count of the total number of Table B records searched directly by FIND. DIRRCD appears in the journal and is accumulated by file, by user, by request, and for the entire system. DIRRCD also can be displayed by the TIME REQUEST command, described in the Model 204 Parameter and Command Reference.
Reclaiming space in files
When a VISIBLE field is redefined, renamed, or deleted, space in the various Model 204 file tables is reclaimed for future reuse. The old name of a renamed field or the name of a deleted field is removed from Table A. If that field had the NUMERIC RANGE parameter, the auxiliary names also are removed. This also is true when a field is redefined from NUMERIC RANGE to NON-RANGE.
When a field name is deleted, the space used by that string in Table A is almost completely reclaimed (all but two bytes of overhead). The count of strings stored on the page is not decremented.
Note
Value string entries for CODED and FRV fields are never removed.
Index entries are removed from Table C for the old name of a renamed field, for a deleted field, and for redefinitions to NON-KEY, NON-RANGE, or NON-FRV.
Index entry spaces for the old name of a renamed field in Table D are reused for the new name. Index entries are removed for deleted fields and for certain redefined fields.
Field entries in Table B are removed for deleted fields that are not preallocated. Occurrences of preallocated fields are deleted, but their space is not deleted.