Inheritance Hierarchy

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Inheritance Hierarchy

Dynamic Server uses an inheritance hierarchy to obtain storage characteristics. Figure 6 shows the inheritance hierarchy for smart-large-object storage characteristics.

Figure 6. Inheritance Hierarchy for Storage Characteristics

This graphic illustrates the inheritance hierarchy for smart-large-object storage characteristics. The graphic contains four horizontal boxes arranged in a vertical line and connected by three down-facing arrows. The boxes are labeled as such: Database server storage characteristics (system defaults and the ONCONFIG file), sbspace storage characteristics (assigned when the database server creates the sbspace), Column-level storage characteristics (assigned with the CREATE TABLE statement), and User-defined storage characteristics (assigned from within an IBM Informix ODBC application.)

System-Specified Storage Characteristics

Dynamic Server uses one of the following sets of storage characteristics as the system-specified storage characteristics:

If the sbspace in which the smart large object is stored specifies a value for a particular storage characteristic, the database server uses the sbspace value as the system-specified storage characteristic.
The database administrator can use the onspaces utility to define storage characteristics for an sbspace.
If the sbspace in which the smart large object is stored does not specify a value for a particular storage characteristic, the database server uses the system default as the system-specified storage characteristic.
The database server defines the system defaults for storage characteristics internally. However, you can specify a default sbspace name with the SBSPACENAME configuration parameter in the ONCONFIG file. Also, an application call to ifx_lo_col_info() or ifx_lo_specset_sbspace() can supply the target sbspace in the smart-large-object specification structure.

Warning:

An error will occur if the sbspacename configuration parameter is not specified and the smart-large-object specification structure does not contain the name of the target sbspace.

It is recommended that you use the system-specified storage characteristics for the disk-storage information. For more information about sbspaces and the description of the onspaces utility, see your IBM Informix: Administrator's Guide.

To use system-specified storage characteristics for a new smart large object

Call ifx_lo_def_create_spec() to allocate a smart-large-object specification structure and to initialize the structure to null values.
Call ifx_lo_create() to create an instance of the smart large object.

Column-Level Storage Characteristics

The CREATE TABLE statement assigns storage characteristics to a database column. The PUT clause of the CREATE TABLE statement specifies storage characteristics for a smart-large-object column. The syscolattribs system catalog table stores the column-level storage characteristics.

To use column-level storage characteristics for a new smart-large-object instance

Call ifx_lo_def_create_spec() to allocate a smart-large-object specification structure and initialize this structure to null values.
Call ifx_lo_col_info() to retrieve the column-level storage characteristics and store them in the specified smart-large-object specification structure.
Call ifx_lo_create() to create an instance of the smart large object.

User-Defined Storage Characteristics

You can define a unique set of storage characteristics for a new smart large object, as follows:

For a smart large object that will be stored in a column, you can override some storage characteristics for the column when you create an instance of a smart large object.
If you do not override some or all of these characteristics, the smart large object uses the column-level storage characteristics.
You can specify a wider set of characteristics for a smart large object because a smart large object is not constrained by table column properties.
If you do not override some or all of these characteristics, the smart large object inherits the system-specified storage characteristics.

To specify user-defined storage characteristics, call an ifx_lo_specset_* function.