HP Integrity NonStop J-Series - Manual (Page 45)

Preparing to Use SMF
HP NonStop Storage Management Foundation User's Guide—523562-007
2-11
Identifying Virtual Disks
Identifying Virtual Disks
Like other disk processes, the SMF VDP is type 3. However, a new subtype value 36
indicates that it is a virtual disk. This subtype is displayed through DEVICEINFO,
DEVICE_GETINFO_ and FILE_GETINFO[LIST]_ file system procedure calls, and
through other processes such as a D-series version of PUP, a G-series version of SCF,
and DSAP. All applications and operational procedures in the SMF environment that
deal with disk subtypes must be able to treat subtype 36 disks appropriately. If they
cannot treat VDPs correctly, they must be modified to avoid disk processes whose
subtype is 36.
TMF Auditing Status
The auditing status of a physical disk can be determined with a call to DEVICEINFO;
however, for a virtual disk, the value FALSE is always returned. Virtual disks may be
assigned to a mixed pool of both audited and non audited disks. Attempts to create an
audited file in a mixed pool will succeed if sufficient space is available on an audited
volume.
Applications that check the auditing status of a volume by calling DEVICEINFO must
be changed to handle VDPs appropriately, or to avoid disk processes whose subtype is
36.
NonStop SQL Temporary Table Placement
When compiling and executing certain queries, the SQL optimizer chooses locations
for temporary tables that hold intermediate query results. Information follows regarding
temporary table placement in the SMF environment:

For serial execution, the optimizer selects a location as it has always done with no
changes.
If the query refers to a table by using the name of a file on a virtual disk, the
optimizer selects that virtual disk for the temporary table. If a virtual disk is
selected, the SMF volume selection algorithm selects the file’s physical location at
run time rather than at compile time. Note that this method may be an advantage
for queries compiled long before they are executed.
If the query refers to a table by using a direct file, the optimizer selects that direct
volume for the temporary table.

For parallel execution the optimizer selects temporary table location by using only
physical volumes.

The optimizer determines scratch volumes at compile time, not at run time.
The =_SQL_EXE_USE_SWAPVOL and =_SQL_TM_system_volume DEFINE
statements may be used to instruct the executor to locate temporary tables on specific
volumes. Application programs can use these DEFINEs to override the optimizer by
using either virtual or direct names. Refer to the SQL/MP Reference Manual for details
on these define statements.