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 on sbspaces, refer to 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, refer to your IBM Informix Dynamic Server 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, refer to the IBM Informix Dynamic Server Administrator's Reference:
The user-data area of smart large objects that are logged does not pass through the physical log, so the PHYSBUFF parameter need not be adjusted for smart large objects.
For more information on the structure of an sbspace, refer to sbspace structure in the disk structures and storage chapter of the IBM Informix Dynamic Server Administrator's Reference. For information on creating an sbspace, see information on the onspaces utility in the IBM Informix Dynamic Server Administrator's Reference.
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