启用In-Memory功能
数据库版本12.1.0.2及其以上版本,inmemory_size参数设置为合适值

SQL> SELECT * FROM V$VERSION;
BANNER                                                                               CON_ID
-------------------------------------------------------------------------------- ----------
Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 - 64bit                         0
PL/SQL Release 12.1.0.2.0 -                                                               0
CORE    12.1.0.2.0                                                                        0
TNS for Linux: Version 12.1.0.2.0 -                                                       0
NLSRTL Version 12.1.0.2.0 -                                                               0
SQL> SHOW PARAMETER inmemory;
NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
inmemory_clause_default              string
inmemory_force                       string      DEFAULT
inmemory_query                       string      ENABLE
inmemory_size                        big integer 200M

创建表
这里可以知道,创建表大小为13631488，但是未使用In-Memory功能

SQL> create table t_xifenfei_in_memory as select * from dba_objects;
Table created.
SQL> SELECT BYTES FROM USER_SEGMENTS WHERE SEGMENT_NAME='T_XIFENFEI_IN_MEMORY';
     BYTES
----------
  13631488
SQL> select TABLE_NAME,INMEMORY_PRIORITY,INMEMORY_DISTRIBUTE,INMEMORY_COMPRESSION from user_tables;
TABLE_NAME                     INMEMORY INMEMORY_DISTRI INMEMORY_COMPRESS
------------------------------ -------- --------------- -----------------
T_XIFENFEI_IN_MEMORY
SQL>  SELECT * FROM V$INMEMORY_AREA;
POOL                       ALLOC_BYTES USED_BYTES POPULATE_STATUS                CON_ID
-------------------------- ----------- ---------- -------------------------- ----------
1MB POOL                     166723584          0 DONE                                3
64KB POOL                     33554432          0 DONE                                3

未使用In-Memory功能测试

SQL> SET AUTOT TRACE
SQL> SELECT * FROM T_XIFENFEI_IN_MEMORY;
90902 rows selected.
Execution Plan
----------------------------------------------------------
Plan hash value: 3598036702
------------------------------------------------------------------------------------------
| Id  | Operation         | Name                 | Rows  | Bytes | Cost (%CPU)| Time     |
------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |                      | 90902 |     9M|   427   (1)| 00:00:01 |
|   1 |  TABLE ACCESS FULL| T_XIFENFEI_IN_MEMORY | 90902 |     9M|   427   (1)| 00:00:01 |
------------------------------------------------------------------------------------------
Statistics
----------------------------------------------------------
          5  recursive calls
          0  db block gets
       7505  consistent gets
       1527  physical reads
          0  redo size
   12125231  bytes sent via SQL*Net to client
      67212  bytes received via SQL*Net from client
       6062  SQL*Net roundtrips to/from client
          2  sorts (memory)
          0  sorts (disk)
      90902  rows processed

这里可以看到未使用In-Memory功能,数据库查询执行计划使用TABLE ACCESS FULL，consistent gets为7505

使用In-Memory功能测试

SQL>  alter table  T_XIFENFEI_IN_MEMORY inmemory;
Table altered.
SQL> select TABLE_NAME,INMEMORY_PRIORITY,INMEMORY_DISTRIBUTE,INMEMORY_COMPRESSION from user_tables;
TABLE_NAME                     INMEMORY INMEMORY_DISTRI INMEMORY_COMPRESS
------------------------------ -------- --------------- -----------------
T_XIFENFEI_IN_MEMORY           NONE     AUTO DISTRIBUTE FOR QUERY
--因为只是把该表设置了INMEMORY,但是未查询过,所以查询V$INMEMORY_AREA中未使用相关内存
SQL> SELECT * FROM V$INMEMORY_AREA;
POOL                       ALLOC_BYTES USED_BYTES POPULATE_STATUS                CON_ID
-------------------------- ----------- ---------- -------------------------- ----------
1MB POOL                     166723584          0 DONE                                3
64KB POOL                     33554432          0 DONE                                3
--进行一次全表扫描
SQL> SELECT COUNT(*) FROM T_XIFENFEI_IN_MEMORY;
  COUNT(*)
----------
     90902
--再次查看，已经使用了分配的In-Memory中内存
SQL> SELECT * FROM V$INMEMORY_AREA;
POOL                       ALLOC_BYTES USED_BYTES POPULATE_STATUS                CON_ID
-------------------------- ----------- ---------- -------------------------- ----------
1MB POOL                     166723584    4194304 DONE                                3
64KB POOL                     33554432     131072 DONE                                3
SQL> SET AUTOT TRACE
SQL> SELECT * FROM T_XIFENFEI_IN_MEMORY;
90902 rows selected.
Execution Plan
----------------------------------------------------------
Plan hash value: 3598036702
---------------------------------------------------------------------------------------------------
| Id  | Operation                  | Name                 | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT           |                      | 90902 |     9M|    20  (45)| 00:00:01 |
|   1 |  TABLE ACCESS INMEMORY FULL| T_XIFENFEI_IN_MEMORY | 90902 |     9M|    20  (45)| 00:00:01 |
---------------------------------------------------------------------------------------------------
Statistics
----------------------------------------------------------
          3  recursive calls
          0  db block gets
          4  consistent gets
          0  physical reads
          0  redo size
    4946298  bytes sent via SQL*Net to client
      67212  bytes received via SQL*Net from client
       6062  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
      90902  rows processed

这里我们可以发现，使用了In-Memory功能之后，数据库consistent gets为4,相比未使用In-Memory之前的7505,性能最少提高近2000倍.