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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
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.
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