Designing Tables and Indexes for Performance › Table Space Performance Recommendations › Use Segmented or Universal Table Spaces › Segmented Table Spaces

Segmented Table Spaces

You gain several advantages by using segmented table spaces. Because the pages in a segment contain only rows from one table, no locking interference with other tables exists. In simple table spaces, rows are intermixed on pages, and if one table page is locked, it can inadvertently lock a row of another table just because it is on the same page. This is not an issue if you have only one table per table space; however, you can obtain following benefits from having a segmented table space for one table:

• If a table scan is performed, the segments belonging to the table being scanned are the only ones accessed; empty pages are not scanned.
• If a mass delete or a DROP table occurs, segment pages are available for immediate reuse, and it is not necessary to run a REORG utility.
• Mass deletes are much faster for segmented table spaces, and they produce less logging, provided the table has not been defined with DATA CAPTURE CHANGES.
• The COPY utility does not have to copy empty pages that are left by a mass delete.
• When inserting records, some read operations can be avoided by using the more comprehensive space map of the segmented table space.