System-specified storage characteristics
The Database Administrator (DBA) establishes system-specified storage
characteristics when he or she initializes the database server and
creates an sbspace with the onspaces utility, as
follows:
- If the onspaces utility has specified a value for a particular storage characteristic, the smart-large-object optimizer uses the onspaces value as the system-specified storage characteristic.
- If the onspaces utility has not specified a value for a particular storage characteristic, the smart-large-object optimizer uses the system default as the system-specified storage characteristic.
The system-specified storage characteristics apply to all smart large objects that are stored in the sbspace, unless a smart large object specifically overrides them with column-level or user-specified storage characteristics.
The onspaces utility establishes storage characteristics
for an sbspace. For the storage characteristics that onspaces can
set as well as the system defaults, see Table 1 and Table 2. For
example, the following call to the onspaces utility
creates an sbspace named sb1 in the /dev/sbspace1 partition:
onspaces -c -S sb1 -p /dev/sbspace1 -o 500 -s 2000
-Df "AVG_LO_SIZE=32"The following table shows the system-specified storage characteristics
for all smart large objects in the sb1 sbspace.
| Disk-storage characteristic | System-specified value | Specified by the onspaces utility |
|---|---|---|
| Size of extent | Calculated by smart-large-object optimizer | system default |
| Size of next extent | Calculated by smart-large-object optimizer | system default |
| Minimum extent size | Calculated by smart-large-object optimizer | system default |
| Size of smart large object | 32 KB (smart-large-object optimizer uses as size estimate) | AVG_LO_SIZE |
| Maximum size of I/O block | Calculated by smart-large-object optimizer | system default |
| Name of sbspace | sb1 | -S option |
| Logging attribute | OFF | system default |
| Last-access time attribute | OFF | system default |
For a smart large object that has system-specified storage characteristics,
the smart-large-object optimizer calculates values for all disk-storage
information except the sbspace name. The DBA can specify a default
sbspace name with the SBSPACENAME configuration parameter in the onconfig file.
However, you must ensure that the location (the name of the sbspace)
is correct for the smart large object that you create. If you do not
specify an sbspace name for a new smart large object, the database
server stores it in this default sbspace. This arrangement can quickly
lead to space constraints.
Important: For new smart large
objects, use the system-specified values of all disk-storage information
except the sbspace name. The smart-large-object optimizer can best
determine most of the values of the storage characteristics. Most
applications only need to specify an sbspace name for their disk-storage
information.