SQL/MX 2.x Reference Manual (H06.10+, J06.03+)

Metadata Tables
HP NonStop SQL/MX Reference Manual—544517-008
10-67
Scratch Disk Management
Scratch Disk Management
These attributes determine how NonStop SQL/MX manages scratch disks for the sort
operation:
About SQL/MX Scratch Disks
NonStop SQL/MX selects a disk to be used for a scratch file from the pool of available
disks. The pool initially consists of the set of all suitable disks. Disks such as optical
disks, phantom disks, and SMS virtual disks are not considered suitable. The disks
specified by the SCRATCH_DISKS_EXCLUDED control are removed. If the
SCRATCH_DISKS control is specified, the disks that are not specified in the
SCRATCH_DISKS control are removed from the pool. From this disk pool, a disk is
selected based on this criteria:
•
The amount of used space on the disk. (rank * 30)
•
The number of scratch files on the disk. (rank * 70)
•
The number of fragments on the disk. (rank * 20)
•
The biggest available fragment on the disk. (inverted rank * 80)
•
Is the disk a preferred disk? (10000)
•
Is the disk the primary disk of the CPU of this process? (100000)
Attribute Setting
SCRATCH_DISKS Set to a list of scratch disk volumes, where each item in the list
has the form [\node.]$volume, and the items in the list are
separated by a comma (,). Use this default to restrict scratch
disks to the volumes specified.
If none of the three scratch disk defaults are set, the system
determines the scratch disk volumes to be used.
SCRATCH_DISKS_
EXCLUDED
Set to a list of scratch disk volumes, where each item in the list
has the form [\node.]$volume, and the items in the list are
separated by a comma (,). Use this default to exclude certain
volumes from being used for scratch disks.
If none of the three scratch disk defaults are set, the system
determines the scratch disk volumes to be used.
SCRATCH_DISKS_
PREFERRED
Set to a list of scratch disk volumes, where each item in the list
has the form [\node.]$volume, and the items in the list are
separated by a comma (,). Use this default to indicate
preference for volumes to be used for scratch disks.
If none of the three scratch disk defaults are set, the system
determines the scratch disk volumes to be used.
SCRATCH_FREESPACE_
THRESHOLD_PERCENT
Indicates how much free space, as a percentage, is left on a
disk as a threshold. When that threshold is reached, hash or
sort operations will use a different disk. If all disks reach their
threshold, NonStop SQL/MX displays an error.
The default value is 10. When disk usage reaches the point
where only 10 percent of the space remains, hash or sort or
operations stop using that disk.