1 相关参数
RESULT_CACHE_MAX_RESULT:指定任一结果可使用的最大高速缓存量,默认值为5%,但可指定1 到100 之间的任一百分比值,可在系统和会话级别上实施此参数;
result_cache_max_size :32k的整数倍,如果将结果高速缓存的值设为0,则会禁用此结果高速缓存,不能超过共享池的75%;
RESULT_CACHE_REMOTE_EXPIRATION:可以指定依赖于远程数据库对象的结果保持有效的时间(以分钟为单位),默认值为0,表示不会使用高速缓存使用远程对象的结果;
result_cache_mode :默认为 MANUAL,即加hint /+ result_cache / 才使用result cache
启用result cache:
alter system set result_cache_max_result=5;
alter system set result_cache_max_size=20m;
2 相关存储过程
查询内存分配情况:
SQL>set serveroutput on ;
SQL> exec dbms_result_cache.memory_report
R e s u l t C a c h e M e m o r y R e p o r t
[Parameters]
Block Size = 1K bytes
Maximum Cache Size = 1280K bytes (1280 blocks)
Maximum Result Size = 64K bytes (64 blocks)
[Memory]
Total Memory = 202160 bytes [0.110% of the Shared Pool]
... Fixed Memory = 5352 bytes [0.003% of the Shared Pool]
... Dynamic Memory = 196808 bytes [0.107% of the Shared Pool]
....... Overhead = 131272 bytes
....... Cache Memory = 64K bytes (64 blocks)
........... Unused Memory = 29 blocks
........... Used Memory = 35 blocks
............... Dependencies = 10 blocks (10 count)
............... Results = 25 blocks
................... SQL = 20 blocks (20 count)
................... Invalid = 5 blocks (5 count)
SQL> select dbms_result_cache.status from dual;
ENABLED
删除所有现有结果并清空高速缓存:EXECUTE DBMS_RESULT_CACHE.FLUSH;
检查:select * from GV$RESULT_CACHE_OBJECTS
使特定结果失效:
begin
DBMS_RESULT_CACHE.INVALIDATE('SH','SALES');
end;
select cache_id,lru_number,db_link,status,bucket_no,hash,name,namespace,type,status
from GV$RESULT_CACHE_OBJECTS where name like '%sales%';
CACHE_ID LRU_NUMBER DB_LINK STATUS BUCKET_NO HASH NAME NAMESPACE TYPE STATUS
3gqafv8xzpk9t535y6dgfmyhjt 0 No Invalid 2055 571566087 "select /*+ result_cache */ prod_id,sum(amount_sold) from sh.sales group by prod_id order by prod_id
" SQL Result** Invalid**
3 执行计划查看SQL> select /*+ result_cache */ prod_id,sum(amount_sold) from sales group by prod_id order by prod_id;
Execution Plan
Plan hash value: 4109827725
--------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | Pstart| Pstop |
| 0 | SELECT STATEMENT | | 72 | 648 | 680 (24)| 00:00:09 | | |
| 1 | RESULT CACHE | g23n3fafz6vxs65351bmca3jq8 | | | | | | |
| 2 | SORT GROUP BY | | 72 | 648 | 680 (24)| 00:00:09 | | |
| 3 | PARTITION RANGE ALL| | 918K| 8075K| 557 (8)| 00:00:07 | 1 | 28 |
| 4 | TABLE ACCESS FULL | SALES | 918K| 8075K| 557 (8)| 00:00:07 | 1 | 28 |
Result Cache Information (identified by operation id):
1 - column-count=2; dependencies=(SH.SALES); name="select /*+ result_cache */ prod_id,sum(amount_sold) from sales group by prod_id order by prod_id"
可以看出为result cache;不使用result cache:
select prod_id,sum(amount_sold) from sales group by prod_id order by prod_id;
Execution Plan
----------------------------------------------------------
Plan hash value: 4109827725
----------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | Pstart| Pstop |
----------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 72 | 648 | 680 (24)| 00:00:09 | | |
| 1 | SORT GROUP BY | | 72 | 648 | 680 (24)| 00:00:09 | | |
| 2 | PARTITION RANGE ALL| | 918K| 8075K| 557 (8)| 00:00:07 | 1 | 28 |
| 3 | TABLE ACCESS FULL | SALES | 918K| 8075K| 557 (8)| 00:00:07 | 1 | 28 |
也可以强制对象使用result cache:alter table sales result_cache(mode force);
取消:alter table sales result_cache(mode default);
4 相关视图
(G)V$RESULT_CACHE_STATISTICS : 列出各种高速缓存设置和内存使用量统计信息
select from V$RESULT_CACHE_STATISTICS
(G)V$RESULT_CACHE_MEMORY : 列出所有内存块和相应的统计信息
select from V$RESULT_CACHE_MEMORY
(G)V$RESULT_CACHE_OBJECTS: 列出所有对象(高速缓存结果和依赖性)及其属性
select cache_id,lru_number,db_link,status,bucket_no,hash,name,namespace,type,status
from GV$RESULT_CACHE_OBJECTS where name like '%sales%';
(G)V$RESULT_CACHE_DEPENDENCY: 列出高速缓存结果之间的依赖性详细信息及依赖性
select b.owner,b.object_name,a.* from V$RESULT_CACHE_DEPENDENCY a,all_objects b where a.object_no=b.object_id;
5 注意事项
1 绑定变量不同,不可以命中
2 最适用于需要访问大量行却仅返回其中一少部分的语句,建议使用在OLAP系统/报表系统中使用
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