oracle 12cR2 smart flash cache实测

最近一直在处理新系统的性能优化问题，这两天特地测试了下oracle 11gR2开始引入的smart flash cache。

其介绍参考MOS文档，How To Size the Database Smart Flash Cache (文档 ID 1317950.1)

The Database Smart Flash Cache is a new feature in Oracle Database 11g Release 2 (11.2).

The Database Smart Flash Cache is a transparent extension of the database buffer cache using solid state device (SSD) technology.

The SSD acts as a Level 2 cache to the (Level 1) SGA.

 

Database Smart Flash Cache can greatly improve the performance of Oracle databases by reducing the amount of disk I/O at a much lower cost than adding an equivalent amount of RAM.

简单的说，他比较适合于系统中绝大部分存储使用机械硬盘，但是又配备了小部分SSD的场景，比如说我们的某个系统4.5T存储，600GB的SSD。

Your database is running on the Solaris or Oracle Linux operating systems.

The flash cache is supported on these operating systems only.

如果不是solaris或者OEL，则启动时报错，这很有可能会是个最大的限制，因为很多企业限定了必须使用RHEL/CENTOS/SUSE。如下：

SQL> startup;

ORA-00439: feature not enabled: Server Flash Cache

这明显就是Oracle设置的障碍。

可以通过DB_FLASH_CACHE_FILE和db_flash_cache_size设置智能闪存的位置以及大小。

下面来看实际效果：

[oracle@oel-12c ~]$ sqlplus "/as sysdba"

SQL*Plus: Release 12.2.0.1.0 Production on 星期五 9月 7 20:13:00 2018

Copyright (c) 1982, 2016, Oracle.  All rights reserved.

连接到:
Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production

SQL> create tablespace my_ts_2 datafile '/u01/app/oracle/oradata/nfs_to_14/my_ts02.dbf' size 1g autoextend on next 10m maxsize unlimited;

表空间已创建。

SQL> create table my_big_table as select * from dba_tables;

表已创建。

SQL> alter table my_big_table move tablespace my_ts_2; --移动到NFS存储上

表已更改。

SQL> insert into my_big_table select * from my_big_table;

已创建 2106 行。

SQL> /

已创建 4212 行。

SQL> /

已创建 8424 行。

SQL> /

已创建 16848 行。

SQL> /

已创建 33696 行。

SQL> /

已创建 67392 行。

SQL> commit;

提交完成。

SQL> /

提交完成。

SQL> insert into my_big_table select * from my_big_table;

已创建 134784 行。

SQL> /

已创建 269568 行。

SQL> commit;

提交完成。

SQL> insert into my_big_table select * from my_big_table;

已创建 539136 行。

SQL> commit;

使用智能闪存：

SQL> set autotrace on;
SQL> select count(1) from my_big_table;

  COUNT(1)
----------
   1078272

已用时间:  00: 00: 33.06

执行计划
----------------------------------------------------------
Plan hash value: 1307946652

---------------------------------------------------------------------------
| Id  | Operation       | Name      | Rows  | Cost (%CPU)| Time      |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |          |    1 | 12973   (1)| 00:00:01 |
|   1 |  SORT AGGREGATE    |          |    1 |           |      |
|   2 |   TABLE ACCESS FULL| MY_BIG_TABLE |   969K| 12973   (1)| 00:00:01 |
---------------------------------------------------------------------------

Note
-----
   - dynamic statistics used: dynamic sampling (level=2)

统计信息
----------------------------------------------------------
    124  recursive calls
      0  db block gets
      47210  consistent gets
      47193  physical reads
    132  redo size
    546  bytes sent via SQL*Net to client
    607  bytes received via SQL*Net from client
      2  SQL*Net roundtrips to/from client
      3  sorts (memory)
      0  sorts (disk)
      1  rows processed

SQL> /

  COUNT(1)
----------
   1078272

已用时间:  00: 00: 03.00

执行计划
----------------------------------------------------------
Plan hash value: 1307946652

---------------------------------------------------------------------------
| Id  | Operation       | Name      | Rows  | Cost (%CPU)| Time      |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |          |    1 | 12973   (1)| 00:00:01 |
|   1 |  SORT AGGREGATE    |          |    1 |           |      |
|   2 |   TABLE ACCESS FULL| MY_BIG_TABLE |   969K| 12973   (1)| 00:00:01 |
---------------------------------------------------------------------------

Note
-----
   - dynamic statistics used: dynamic sampling (level=2)

统计信息
----------------------------------------------------------
      0  recursive calls
      0  db block gets
      47094  consistent gets
      47006  physical reads
      0  redo size
    546  bytes sent via SQL*Net to client
    607  bytes received via SQL*Net from client
      2  SQL*Net roundtrips to/from client
      0  sorts (memory)
      0  sorts (disk)
      1  rows processed

SQL> /

  COUNT(1)
----------
   1078272

已用时间:  00: 00: 04.54

执行计划
----------------------------------------------------------
Plan hash value: 1307946652

---------------------------------------------------------------------------
| Id  | Operation       | Name      | Rows  | Cost (%CPU)| Time      |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |          |    1 | 12973   (1)| 00:00:01 |
|   1 |  SORT AGGREGATE    |          |    1 |           |      |
|   2 |   TABLE ACCESS FULL| MY_BIG_TABLE |   969K| 12973   (1)| 00:00:01 |
---------------------------------------------------------------------------

Note
-----
   - dynamic statistics used: dynamic sampling (level=2)

统计信息
----------------------------------------------------------
      0  recursive calls
      0  db block gets
      47094  consistent gets
      47020  physical reads
      0  redo size
    546  bytes sent via SQL*Net to client
    607  bytes received via SQL*Net from client
      2  SQL*Net roundtrips to/from client
      0  sorts (memory)
      0  sorts (disk)
      1  rows processed

SQL> /

  COUNT(1)
----------
   1078272

已用时间:  00: 00: 02.24

不使用智能闪存：

SQL> alter system set db_flash_cache_size=0 ;

系统已更改。

已用时间:  00: 00: 01.01
SQL> select count(1) from my_big_table;

  COUNT(1)
----------
   1078272

已用时间:  00: 00: 30.75

执行计划
----------------------------------------------------------
Plan hash value: 1307946652

---------------------------------------------------------------------------
| Id  | Operation       | Name      | Rows  | Cost (%CPU)| Time      |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |          |    1 | 12973   (1)| 00:00:01 |
|   1 |  SORT AGGREGATE    |          |    1 |           |      |
|   2 |   TABLE ACCESS FULL| MY_BIG_TABLE |   969K| 12973   (1)| 00:00:01 |
---------------------------------------------------------------------------

Note
-----
   - dynamic statistics used: dynamic sampling (level=2)

统计信息
----------------------------------------------------------
      0  recursive calls
      0  db block gets
      47094  consistent gets
      47020  physical reads
      0  redo size
    546  bytes sent via SQL*Net to client
    607  bytes received via SQL*Net from client
      2  SQL*Net roundtrips to/from client
      0  sorts (memory)
      0  sorts (disk)
      1  rows processed

SQL> /

  COUNT(1)
----------
   1078272

已用时间:  00: 00: 32.20

执行计划
----------------------------------------------------------
Plan hash value: 1307946652

---------------------------------------------------------------------------
| Id  | Operation       | Name      | Rows  | Cost (%CPU)| Time      |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |          |    1 | 12973   (1)| 00:00:01 |
|   1 |  SORT AGGREGATE    |          |    1 |           |      |
|   2 |   TABLE ACCESS FULL| MY_BIG_TABLE |   969K| 12973   (1)| 00:00:01 |
---------------------------------------------------------------------------

Note
-----
   - dynamic statistics used: dynamic sampling (level=2)

统计信息
----------------------------------------------------------
      0  recursive calls
      0  db block gets
      47094  consistent gets
      47020  physical reads
      0  redo size
    546  bytes sent via SQL*Net to client
    607  bytes received via SQL*Net from client
      2  SQL*Net roundtrips to/from client
      0  sorts (memory)
      0  sorts (disk)
      1  rows processed

SQL> /

  COUNT(1)
----------
   1078272

已用时间:  00: 00: 17.56

执行计划
----------------------------------------------------------
Plan hash value: 1307946652

---------------------------------------------------------------------------
| Id  | Operation       | Name      | Rows  | Cost (%CPU)| Time      |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |          |    1 | 12973   (1)| 00:00:01 |
|   1 |  SORT AGGREGATE    |          |    1 |           |      |
|   2 |   TABLE ACCESS FULL| MY_BIG_TABLE |   969K| 12973   (1)| 00:00:01 |
---------------------------------------------------------------------------

Note
-----
   - dynamic statistics used: dynamic sampling (level=2)

统计信息
----------------------------------------------------------
      0  recursive calls
      0  db block gets
      47094  consistent gets
      47019  physical reads
      0  redo size
    546  bytes sent via SQL*Net to client
    607  bytes received via SQL*Net from client
      2  SQL*Net roundtrips to/from client
      0  sorts (memory)
      0  sorts (disk)
      1  rows processed

SQL> /

  COUNT(1)
----------
   1078272

已用时间:  00: 00: 15.11

执行计划
----------------------------------------------------------
Plan hash value: 1307946652

---------------------------------------------------------------------------
| Id  | Operation       | Name      | Rows  | Cost (%CPU)| Time      |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |          |    1 | 12973   (1)| 00:00:01 |
|   1 |  SORT AGGREGATE    |          |    1 |           |      |
|   2 |   TABLE ACCESS FULL| MY_BIG_TABLE |   969K| 12973   (1)| 00:00:01 |
---------------------------------------------------------------------------

Note
-----
   - dynamic statistics used: dynamic sampling (level=2)

统计信息
----------------------------------------------------------
      0  recursive calls
      0  db block gets
      47094  consistent gets
      47019  physical reads
      0  redo size
    546  bytes sent via SQL*Net to client
    607  bytes received via SQL*Net from client
      2  SQL*Net roundtrips to/from client
      0  sorts (memory)
      0  sorts (disk)
      1  rows processed

SQL> /

  COUNT(1)
----------
   1078272

已用时间:  00: 00: 15.69

如上所述，性能相差了6-7倍。可见智能闪存效果还是不错的。

不过需要注意的是，如果95%+的常用数据都已经在iops足够高的磁盘上了比如SSD，这个时候又拿一部分SSD作为智能缓存，性能反而会下降比直接访问磁盘高达1倍。

在oracle 11g中，闪存文件只能配置1个，在12c中没有这个限制了。