oracle 12c inmemory

1. enable inmemory 

   inmemory_size = 20G ( parameter setup )

   (inmemory_clause_default :  default action when inmemory object make. )

   * disable / enable inmemory query at session level.

     alter session set inmemory_query = disable

2.  apply inmemory option for object

   apply like the following syntax

   "create table test1 (id number, name varchar2(10)) inmemory"   

   or

   alter table test1 inmemory

   or 

 

   alter table test1  inmemory memcompress for query low (id) no inmemory (name)    -- specific column apply

   * view table related of system inmemory statistics

     

    select * from v$im_col_cu;

    select table_name, segment_column_id, column_name, inmemory_compression from v$im_column_level;

    select owner, segment_name, populate_status, bytes, inmemory_size, inmemory_compression,

            bytes/inmemory 

    from v$im_segments;

    ==> After you query that table, it only store that table in inmemory.

    -- query object info of inmemory 

    select table_name, cache, inmemory_compression, inmemory_priority, inmemory_distribute 

    from dba_tables where table_name = 'TEST1'

    * inmemory option

    - for dml  : optimize dml operation  

    - for query low , for query high : focus on query performance.

    - for capacity low,  for capacity high  : focus on decreasing object size using compression

3. query 

    select count(id) from test1 where id is not null;

 

    select id, count(*) 

    from test1

    group by id;