Database server administrators sometimes need to track disk use by a particular table. A data tblspace contains all the disk space allocated to a given table or table fragment (if the table is fragmented) for data rows. Each index on the table is stored in a separate index tblspace. Any associated TEXT or BYTE data is stored in another separate tblspace: a blob tblspace.
The data tblspace contains the following types of pages:
The index tblspace contains the following types of pages:
The blob tblspace contains the follownig types of pages:
Figure 60 illustrates the tblspaces for three tables that form part of the stores_demo database. Only one table (or table fragment) exists per tblspace. An index resides in a separate tblspace from the associated table. Blobpages represent TEXT or BYTE data stored in a dbspace.
The database server allocates the pages that belong to a tblspace as extents. Although the pages within an extent are contiguous, extents might be scattered throughout the dbspace where the table resides (even on different chunks). Figure 62 depicts this situation with two noncontiguous extents that belong to the tblspace for table_1 and a third extent that belongs to the tblspace for table_2. A table_2 extent is positioned between the first table_1 extent and the second table_1 extent. When this situation occurs, the extents are interleaved. Because sequential access searches across table_1 require the disk head to seek across the table_2 extent, performance is worse than if the table_1 extents were contiguous. For instructions on how to avoid and eliminate interleaving extents, see your IBM Informix: Performance Guide.