Changing storage characteristics of smart large objects

When you create an sbspace, but do not specify values in the -Df option of the onspaces -c -S command, you use the defaults for the storage characteristics and attributes (such as logging and buffering). After you monitor sbspaces, you might want to change the storage characteristics, logging status, lock mode, or other attributes for new smart large objects.

The database administrator or programmer can use the following methods to override these default values for storage characteristics and attributes:
  • The database administrator can use one of the following onspaces options:
    • Specify values when the sbspace is first created with the onspaces -c -S command.
    • Change values after the sbspace is created with the onspaces -ch command.

    Specify these values in the tag options of the -Df option of onspaces. For more information about the onspaces utility, see the HCL Informix Administrator's Reference.

  • The database administrator can specify values in the PUT clause of the CREATE TABLE or ALTER TABLE statements.

    These values override the values in the onspaces utility and are valid only for smart large objects that are stored in the associated column of the specific table. Other smart large objects (from columns in other tables) might also reside in this same sbspace. These other columns continue to use the storage characteristics and attributes of the sbspace that onspaces defined (or the default values, if onspaces did not define them) unless these columns also used a PUT clause to override them for a particular column.

    If you do not specify the storage characteristics for a smart-large-object column in the PUT clause, they are inherited from the sbspace.

    If you do not specify the PUT clause when you create a table with smart-large-object columns, the database server stores the smart large objects in the system default sbspace, which is specified by the SBSPACENAME configuration parameter in the ONCONFIG file. In this case, the storage characteristics and attributes are inherited from the SBSPACENAME sbspace.

  • Programmers can use functions in the DataBlade API and Informix® ESQL/C to alter storage characteristics for a smart-large-object column.

    For information about the DataBlade API functions for smart large objects, see the HCL Informix DataBlade API Programmer's Guide. For information about the Informix ESQL/C functions for smart large objects, see the HCL Informix Enterprise Replication Guide.

Table 1 summarizes the ways to alter the storage characteristics for a smart large object.

Table 1. Altering storage characteristics and other attributes of an sbspace
Storage Character-istic or Attribute System Default Value System-Specified Storage Characteristics Specified by -Df Option in onspaces Utility Column-Level Storage Characteristics Specified by PUT clause of CREATE TABLE or ALTER TABLE Storage Characteris-tics Specified by a DataBlade API Function Storage Characteris-tics Specified by an ESQL/C Function
Last-access time OFF ACCESSTIME KEEP ACCESS TIME, NO KEEP ACCESS TIME Yes Yes
Lock mode BLOB LOCK_MODE No Yes Yes
Logging status OFF LOGGING LOG, NO LOG Yes Yes
Data integrity HIGH INTEG No HIGH INTEG, MODERATE INTEG Yes No
Size of extent None EXTENT_SIZE EXTENT SIZE Yes Yes
Size of next extent None NEXT_SIZE No No No
Minimum extent size 2 kilobytes on Windows 4 kilobytes on UNIX MIN_EXT_SIZE No No No
Size of smart large object 8 kilobytes 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 Estimated size of a particular smart large object Maximum size of a particular smart large object
Buffer pool usage ON BUFFERING No LO_BUFFER and LO_ NOBUFFER flags LO_BUFFER and LO_ NOBUFFER flags
Name of sbspace SBSPACE-NAME Not in -Df option. Name specified in onspaces -S option. Name of an existing sbspace in which a smart large object resides: PUT ... IN clause Yes Yes
Fragmenta-tion across multiple sbspaces None No Round-robin distribution scheme: PUT ... IN clause Round-robin or expression-based distribution scheme Round-robin or expression-based distribution scheme
Last-access time OFF ACCESSTIME KEEP ACCESS TIME, NO KEEP ACCESS TIME Yes Yes

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