Measure Reference Manual

• Both DISCOPEN and DISKFILE measure physical access to a file. When deciding when to use
DISCOPEN and when to use DISKFILE, consider:
◦ DISCOPEN creates a separate counter record for each file open. Opener processes are
identified individually. If the same process opens a file more than once, multiple DISCOPEN
records are created.
◦ DISKFILE measures disk file access per file. DISKFILE creates one counter record for each
measured file and does not track individual opener processes.
◦ For indirect opens, such as an open of an alternate-key file, DISCOPEN creates a separate
record. DISKFILE does not create a separate record for indirect opens.
◦ Both DISCOPEN and DISKFILE create a new record if a file closes and reopens during a
measurement.
◦ DISCOPEN provides a detailed view of disk-file activity. DISCOPEN counters are especially
useful for detecting potential problems with the structure of key-sequenced database files.
◦ If you do not need a high level of detail, DISKFILE reduces the amount of data you must
analyze while still letting you detect potential problems with file structure and contention.
To measure logical access to a file, use the FILE entity type. For a description, see FILE
(page 227).
• DISCOPEN and DISKFILE entities count requests to the storage driver software. These counts
do not distinguish between requests that are satisfied out of cache (logical request only) and
requests that are satisfied through an I/O transfer (physical I/O).
In writes to mirrored disks, the request counts are incremented once even though two physical
writes occurred.
Usage Notes for G-Series DISCOPEN Entities
• The SQL-OPERATION-TIME counter, when summed across all DISCOPEN records for a disk,
is not inclusive of all DP2 processing time or of all SQL-related processing time. Many DP2
processing activities cannot be associated with a particular DISCOPEN. Because
non-SQL-OPERATION-TIME operations are too small in duration to be measured, the intent of
the SQL-OPERATION-TIME counter is to identify SQL operations that are major consumers of
DP2 process-busy-time and to associate the requests with a particular opening process.
• In the Guardian file system, a file can be opened through normal Guardian file naming or
through the OSS file pathname: /G/volume/subvol/filename.
• For OSS file-system opens of the DISCOPEN record, the OSS file pathname that was used to
open the file is displayed. For Guardian file-system opens of the DISCOPEN record, the PATHID
information for the record is incomplete, and the request to translate the information cannot
occur. In this case, the OSS file pathname displayed is obtained from translation of the
Guardian file name and CRVSN value. If more than one path to the file name is defined, all
OSS file pathnames are displayed.
• A LIST DISCOPEN * report request or a report request from the Guardian file system displays
an OSS file pathname for the record, but any subsequent LIST requests do not return the same
OSS file pathname record. This behavior indicates that the file-system access was through the
Guardian file system or that the file being listed is a Guardian file name. For more information
on the distinctions between the Guardian and OSS file systems and environments, see the
Open System Services User’s Guide.
• In Measure G11 and later PVUs, ANSI SQL names appear in displays.
216 Entities and Counters