To save storage space
increased io performance
reduced memory use
reduced redo
less undo
2.Which tables are to be compressed ?
Tables which are not updated or inserted frequently but are queried are ideal candidate for table compression
3.How to identify which tables are compressed ?
Select table_name, compression, compress_for from user_tables;
4.Where is it used ?
Its used mainly in dw projects and oltp
Creating compressed tables takes more time than uncompressed table creation as compression requires some cpu processing
5.What can be compressed ?
Tablespace ,table or partition
6.Compression options
Nocompress : default action table is not compressed
Compress : compression is enabled on the table or partition during direct path inserts only
Compress for direct_load operations - same as above
Compress for all operations : suitable for oltp systems , enables compression for all levels including regular dml statements
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