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stay Oracle in , What is a compressed index ?


     
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Oracle Databases can use key compression (Key Compression) To compress B-Tree The part of an index or index that organizes the values of a primary key column in a table . Key compression can greatly reduce the space used by the index , An index that uses key compression is called a compressed index . Compression of the index is more about saving storage space , Reduce I/O Time . Compression also introduces storage overhead , It's just that a lot of the time compression saves more space than compression requires , So the overall storage cost is reduced after compression .

You can use the following SQL Rebuild the index into a compressed or uncompressed index :

1ALTER INDEX EMPLOYEE_LAST_NAME_IDX REBUILD NOCOMPRESS;-- Uncompressed
2ALTER INDEX EMPLOYEE_LAST_NAME_IDX REBUILD COMPRESS;-- Compress 
     

All compressed indexes can be accessed through the following SQL Statement get :

1SELECT * FROM DBA_INDEXES D WHERE D.COMPRESSION='ENABLED';