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标题: oracle 12cR2 smart flash cache [打印本页]

作者: 郑全 时间: 2019-8-8 16:16
标题: oracle 12cR2 smart flash cache
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 2018Copyright (c) 1982, 2016, Oracle.  All rights reserved.连接到: Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit ProductionSQL> 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 processedSQL> /  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 processedSQL> /  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 processedSQL> /  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: 01.01SQL> 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 processedSQL> /  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 processedSQL> /  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 processedSQL> /  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 processedSQL> /  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。

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