Storage-characteristics hierarchy

HCL Informix® uses the storage-characteristics hierarchy to obtain the storage characteristics for a new smart large object.

The following figure shows the storage-characteristics hierarchy.

Figure 1. Storage-characteristics hierarchy

For a given storage characteristic, any value defined at the column level overrides the system-specified value, and any user-level value overrides the column-level value. The following table summarizes the ways to specify disk-storage information for a smart large object.

Table 1. Specifying disk-storage information
Storage information	System default value	Storage characteristic specified by onspaces utility	Column-level storage characteristic specified by the PUT clause of CREATE TABLE	User-defined storage characteristic specified by a function
Size of extent	Calculated by smart-large-object optimizer	EXTENT_SIZE	EXTENT SIZE	Yes
Size of next extent	Calculated by smart-large-object optimizer	NEXT_SIZE	No	No
Minimum extent size	Four kilobytes	MIN_EXT_SIZE	No	No
Size of smart large object	Calculated by smart-large-object optimizer	Average size of all smart large objects in sbspace: AVG_LO_SIZE	No	Estimated size of a particular smart large object Maximum size of a particular smart large object
Maximum size of I/O block	Calculated by smart-large-object optimizer	MAX_IO_SIZE	No	No
Name of sbspace	SBSPACENAME	-S option	Name of an existing sbspace that stores a smart large object: IN clause	Yes

For most applications, use the values for the disk-storage information that the smart-large-object optimizer determines. If you know the size of the smart large object, it is recommended that you specify this size as a user-specified storage characteristic, instead of as a system-specified or column-level storage characteristic.

For more information about any of the disk-storage information in Specifying disk-storage information , see Disk-storage information.

The following table summarizes the ways to specify attribute information for a smart large object.

Table 2. Specifying attribute information
Storage information	System default value	Storage characteristic specified by the onspaces utility	Column-level storage characteristic specified by the PUT clause of CREATE TABLE	User-defined storage characteristic specified by a function
Logging	OFF	LOGGING	LOG, NO LOG	Yes
Last-access time	OFF	ACCESSTIME	KEEP ACCESS TIME NO KEEP ACCESS TIME	Yes
Buffering mode	OFF	BUFFERING	No	Yes
Lock mode	Lock entire smart large object	LOCK_MODE	No	Yes
Data integrity	High integrity	No	HIGH INTEG, MODERATE INTEG	Yes

For more information about any of the attributes in Specifying attribute information, see Attribute information.

The following table summarizes the ways to specify open-mode information for a smart large object.

Table 3. Specifying open-mode information
Storage information	System default value	Storage characteristic specified by the onspaces utility	Column-level storage characteristic specified by the PUT clause of CREAT TABLE	User-defined storage characteristic specified by a function
Open-mode information	Default open mode	No	No	Yes