系统是linux 6.4
Oracle版本  12.1.0.2.0             
SQL> r
  1* select segment_name,inmemory from dba_segments where owner='SCOTT'
SEGMENT_NAME         INMEMORY
-------------------- --------
OBJ2                 DISABLED
OBJ                  DISABLED
SQL> select count(*) from obj;
  COUNT(*)
----------
     90165
Execution Plan
----------------------------------------------------------
Plan hash value: 1612036541
-------------------------------------------------------------------
| Id  | Operation          | Name | Rows  | Cost (%CPU)| Time     |
-------------------------------------------------------------------
|   0 | SELECT STATEMENT   |      |     1 |   393   (1)| 00:00:01 |
|   1 |  SORT AGGREGATE    |      |     1 |            |          |
|   2 |   TABLE ACCESS FULL| OBJ  | 90165 |   393   (1)| 00:00:01 |
-------------------------------------------------------------------
Statistics
----------------------------------------------------------
         11  recursive calls
          0  db block gets
       1420  consistent gets
       1409  physical reads
          0  redo size
        544  bytes sent via SQL*Net to client
        551  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          2  sorts (memory)
          0  sorts (disk)
          1  rows processed


SQL> alter table obj inmemory;
Table altered.

SQL> select segment_name,inmemory from dba_segments where owner='SCOTT';
SEGMENT_NAME         INMEMORY
-------------------- --------
OBJ2                 DISABLED
OBJ                  ENABLED
SQL> select count(*) from obj;
  COUNT(*)
----------
     90165

Execution Plan
----------------------------------------------------------
Plan hash value: 1612036541
----------------------------------------------------------------------------
| Id  | Operation                   | Name | Rows  | Cost (%CPU)| Time     |
----------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |      |     1 |    15   (0)| 00:00:01 |
|   1 |  SORT AGGREGATE             |      |     1 |            |          |
|   2 |   TABLE ACCESS INMEMORY FULL| OBJ  | 90165 |    15   (0)| 00:00:01 |
----------------------------------------------------------------------------
Statistics
----------------------------------------------------------
          9  recursive calls
          0  db block gets
       1422  consistent gets
       1409  physical reads
          0  redo size
        544  bytes sent via SQL*Net to client
        551  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          2  sorts (memory)
          0  sorts (disk)
          1  rows processed

逻辑读和物理读都没减少