線上重建索引

ALTER INDEX emp_name REBUILD ONLINE;

--維護索引是需要知道的:

Monitoring Space Use of Indexes

If key values in an index are inserted, updated, and deleted frequently, the index can lose its acquired space efficiently over time. Monitor index efficiency of space usage at regular intervals by first analyzing the index structure, using the

ANALYZE INDEX ... VALIDATE STRUCTURE

statement, and then querying the

INDEX_STATS

view:

SELECT PCT_USED FROM INDEX_STATS WHERE NAME = 'index';

      

The percentage of index space usage varies according to how often index keys are inserted, updated, or deleted. Develop a history of average efficiency of space usage for an index by performing the following sequence of operations several times:

• Analyzing statistics
• Validating the index
• Checking

  PCT_USED

• Dropping and rebuilding (or coalescing) the index

When you find that index space usage drops below its average, you can condense the index space by dropping the index and rebuilding it, or coalescing it.

Viewing Index Information

The following views display information about indexes:

View	Description
DBA_INDEXES ALL_INDEXES USER_INDEXES	DBA view describes indexes on all tables in the database. ALL view describes indexes on all tables accessible to the user. USER view is restricted to indexes owned by the user. Some columns in these views contain statistics that are generated by the DBMS_STATS package or ANALYZE statement.
DBA_IND_COLUMNS ALL_IND_COLUMNS USER_IND_COLUMNS	These views describe the columns of indexes on tables. Some columns in these views contain statistics that are generated by the DBMS_STATS package or ANALYZE statement.
DBA_IND_EXPRESSIONS ALL_IND_EXPRESSIONS USER_IND_EXPRESSIONS	These views describe the expressions of function-based indexes on tables.
INDEX_STATS	Stores information from the last ANALYZE INDEX ... VALIDATE STRUCTURE statement.
INDEX_HISTOGRAM	Stores information from the last ANALYZE INDEX ... VALIDATE STRUCTURE statement.
V$OBJECT_USAGE	Contains index usage information produced by the ALTER INDEX ... MONITORING USAGE functionality.