Structure of Fragmented Tables

Although table fragmentation is transparent to applications, as database server administrator you should be aware of how the database server allocates disk space for table fragments and how the database server identifies rows in those fragments.

Each table fragment has its own tblspace with a unique tblspace_id or fragment_id. Figure 1 shows the disk allocation for a fragmented table that resides in named fragments of the same dbspace.
Figure 1. Disk Structures for a Fragmented Table
begin figure description - The figure shows two Dbspaces, Dbspace one and two. Within each Dbspace is a Tblspace; within each Tblspace are two extents, extents one and two. Each extent contains a table, and each table is fragmented into six pieces. end figure description -

Attached Indexes

With an attached index, the index and data are fragmented in the same way. You can decide whether to store the index pages with the corresponding data pages in the same dbspace or store them in separate dbspaces. For information on choosing a fragmentation strategy, see the HCL Informix® Performance Guide.

Detached Indexes

For detached indexes, the table fragment and index fragment are stored in tblspaces in separate dbspaces.

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