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 onspaces utility establishes storage characteristics for an sbspace. For the storage characteristics that onspaces can set as well as the system defaults, see Specifying disk-storage information and Specifying attribute information. 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.

Table 1. System-specified storage characteristics for 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.