In-Memory Column Store (IM column store): The IM Column Store stores the data by column rather than row. The columnar format exists only in memory. It is an optional STATIC component of the SGA. IM Column store sub divided into two pools: 1 MB pool—Store the actual column formatted data 64k Pool--- Store the metadata about the objects. Objects that are smaller than 64KB are not populated into memory. No application changes are required. Stores copies of tables and partitions in a special columnar format optimized for rapid scans. IM column store is made up of multiple In-Memory Compression Units (IMCUs). It is not a replacement of buffer cache, but acts as a supplement so that both memory areas store the same data in different formats. The database keeps the columnar data transitionally consistent with the buffer cache. By default, only objects specified as INMEMORY using DDL are candidates to be populate
