File statistics and tuning

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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.

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.