Unisoft Technologies Nagpur

Table Compression: Overview Oracle Database supports three methods of table compression: • Basic table compression • OLTP table compression Oracle Corporation recommends to compress all data to reduce storage costs. The Oracle database can use table compression to eliminate duplicate values in a data block. For tables with highly redundant data, compression saves disk space and reduces memory use in the database buffer cache. Table compression is transparent to database applications. • The table_compression clause is valid only for heap-organized tables. The COMPRESS keyword enables table compression. The NOCOMPRESS keyword disables table compression. NOCOMPRESS is the default. • With basic compression, the Oracle database compresses data at the time of performing bulk load using operations such as direct loads or CREATE TABLE AS SELECT . • With COMPRESS FOR OLTP , the Oracle database compresses data during all DML operations on the table. 

Understand Deferred Segment Creation Beginning with Oracle Database 11 g Release 2, when you create heap-organized tables in a locally managed tablespace, the database defers table segment creation until the first row is inserted. In addition, segment creation is deferred for any LOB columns of the table, any indexes created implicitly as part of table creation, and any indexes subsequently explicitly created on the table. Note: In Release 11.2.0.1, deferred segment creation is not supported for partitioned tables. This restriction is removed in release 11.2.0.2 and later. The advantages of this space allocation method are the following: It saves a significant amount of disk space in applications that create hundreds or thousands of tables upon installation, many of which might never be populated. It reduces application installation time. There is a small performance penalty when the first row is inserted, because the new segment must be created at that ...