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

begin figure description - This figure is described in the surrounding text. - end figure description
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 DataBlade® API 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 DataBlade API 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 DataBlade API function
Open-mode information Default open mode No No Yes