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Unformatted text preview: one index
• 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...
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- Summer '10