Access smart large objects

The database server accesses smart large objects through the shared-memory buffers, in the same way that it accesses data that is stored in a dbspace. However, the user-data portion of a smart large object is buffered at a lower priority than normal buffer pages to prevent flushing data of higher value out of the buffer pool. Buffering permits faster access to smart large objects that are accessed frequently.

A smart large object is stored in an sbspace. You cannot store simple large objects in an sbspace, and you cannot store smart large objects in a blobspace. An sbspace consists of a user-data area and a metadata area. The user-data area contains the smart-large-object data. The metadata area contains information about the content of the sbspace. For more information about sbspaces, see Sbspaces.

Because smart large objects pass through the shared-memory buffer pool and can be logged, you must consider them when you allocate buffers. Use the BUFFERPOOL configuration parameter to allocate shared-memory buffers. As a general rule, try to have enough buffers to hold two smart-large-object pages for each concurrently open smart large object. (The additional page is available for read-ahead purposes.) For more information about tuning buffers for smart large objects, see your HCL Informix® Performance Guide.

Use the LOGBUFF configuration parameter to specify the size of the logical-log buffer. For information about setting each of the following configuration parameters, see the HCL Informix Administrator's Reference:

The user-data area of smart large objects that are logged does not pass through the physical log, so changing the PHYSBUFF parameter is not required for smart large objects.

For more information about the structure of an sbspace, see sbspace structure in the disk structures and storage chapter of the HCL Informix Administrator's Reference. For information about creating an sbspace, see information about the onspaces utility in the HCL Informix Administrator's Reference.

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