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AdministeringIn addition to administering the database server, you can tune performance, replicate data, and archive data.
System administrationThese topics contain concepts, procedures, and reference information for database and database server administrators to use for managing and tuning HCL Informix® database servers.
Performance GuideThe Informix® Performance Guide describes how to configure and operate your HCL Informix® database server to improve overall system throughput and to improve the performance of SQL queries.
Table performance considerationsSome performance issues are associated with unfragmented tables and table fragments.
Managing extentsAs you add rows to a table, the database server allocates disk space in units called extents. Each extent is a block of physically contiguous pages from the dbspace. Even when the dbspace includes more than one chunk, each extent is allocated entirely within a single chunk, so that it remains contiguous.
Monitoring the upper limit on extents and extent interleavingYou can monitor the upper limit on the number of extents. You can also check for and eliminate extent interleaving.
Eliminating interleaved extentsYou can eliminate interleaved extents by reorganizing the tables with the UNLOAD and LOAD statements, creating or altering an index to cluster, or using the ALTER TABLE statement.
Reorganizing dbspaces and tables to eliminate extent interleavingYou can rebuild a dbspace to eliminate interleaved extents so that the extents for each table are contiguous.

Reorganizing dbspaces and tables to eliminate extent interleaving

You can rebuild a dbspace to eliminate interleaved extents so that the extents for each table are contiguous.

About this task

The order of the reorganized tables within the dbspace is not important, but the pages of each reorganized table should be contiguous so that no lengthy seeks are required to read the table sequentially. When the disk arm reads a table nonsequentially, it ranges only over the space that table occupies.

This figure shows contiguous extents for three tables. — Figure 1: A dbspace reorganized to eliminate interleaved extents

Procedure

To reorganize tables in a dbspace:

For DB-Access users: Copy the tables in the dbspace individually to tape with the UNLOAD statement in DB-Access.
Drop all the tables in the dbspace.
Re-create the tables with the LOAD statement or the dbload utility.

Results

The LOAD statement re-creates the tables with the same properties they had before, including the same extent sizes.

You can also unload a table with the onunload utility and reload the table with the companion onload utility.

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