8-Storage Structure

If a table has three indexes three index segments are

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: one index segment. • If a table has three indexes, three index segments are used • The purpose of this segment is to look up the location of rows in a table based on a specific key Index Storage Structure Tathagata Bhattacharjee • In an index-organized table, data is stored within the index based on the key value. • An index-organized table does not need a table lookup, because all the data can be retrieved directly from the index tree Index-Organized Table Storage Structure Tathagata Bhattacharjee • An index can be partitioned and spread across several tablespaces. • Each partition in the index corresponds to a segment and cannot span multiple tablespaces • The primary use of a partitioned index is to minimize contention by spreading index I/O. Index Partition Storage Structure Tathagata Bhattacharjee • An undo segment is used by a transaction that is making changes to a database • Before changing the data or index, the old value is stored in the undo segment. This allows a user to undo changes made Undo Segment Storage Structure Tathagata Bhattacharjee • When a user executes command such as CREATE INDEX, SELECT DISTINCT and SELECT GROUP BY, the Oracle server tries to perform sorts in memory. • When a sort needs more space than the space available in memory, intermediate results are written to the disk. • Temporary segments are used to store these intermediate results Temporary Segment Storage Structure Tathagata Bhattacharjee • One or more column in a table can be used to store large objects (LOBs) such as text documents, images or videos. • If the column is large, the Oracle server stores these values in separate segments known as LOB segments • The tables contains only a locator or a pointer to the location of the corresponding LOB data LOB Segment Storage Structure Tathagata Bhattacharjee • A column in a table may be made up of a user-defined table as in the case of items within an order • In such case, the inner table, which is known as a nested table, is stored as a separate segment Nested Tables Storage Structure Tathagata Bhattacharjee • A bootstrap segment, also...
View Full Document

Ask a homework question - tutors are online