oracle 11g 之 result cache
oracle 11g 之 result cache
今天是2013-10-12,打算最近时间研究一下shared pool的相关原理以及awr报告分析。今天学习一下在oracle 11g shared pool中新增的一个cache 那就是result cache。
从上图可以看出在oracle 11g 的shared pool中存有对sql进行存储、存储sql执行计划、sql解析树等信息的library cache可以通过查看v$librarycahe视图了解其分配情况,以及row CACHE(data dictionary cache)可以查看v$rowcache视图了解其分配情况,对于这两部分内容咱不讨论,但是可以看一下如下这个图,大体明白这两个component的作用原理。
现在开始研究一下result cache,对于oracle 11g 分为client result cache以及server result cache,前者在client进行内存的分配,后者对于数据库server进行内存分配,现在看一下server result cache(如下皆是server result cache内容)。说白了,result cache 就是为了缓存结果集的一块区域,主要是缓存sql 查询结果集以及pl/sql function结果集。
对于 result cache存在几个参数,如下:
result_cache_max_result integer
result_cache_max_size big integer
result_cache_mode string MANUAL(AUTO、FORCE)
1)、result_cache_max_result 表示对于单个的缓存结果占整个result cache 大小的百分比。
2)、result_cache_max_size 参数用于设置该result cache 的大小,是一个动态参数,该参数为0 则说明result cache 功能禁用了。
3)、result_cache_mode,表示result cache的模式,其中有manual、force。manual 表示只有使用hints(result_cache)才可以对其结果进行缓存且当从result cache中获取结果集的时候也必须使用hints(result cache)参数;force表示强制对结果集进行缓存 oracle对该参数的设置不建议,如下:
FORCE mode is not recommended because the database and clients will attempt to cache all queries, which may create significant performance and latching overhead. Moreover, because queries that call non-deterministic PL/SQL functions are also cached, enabling the result cache in such a broad-based manner may cause material changes to the results.
如果需要不对操作进行缓存可以使用hints(no_result_cache)进行设置。
如下是练习过程:
一、
设置result cache 大小为20M,模式为manual,每个结果集占用总的cache比例为50%(为了测试方便);
SQL> alter system set result_cache_mode=manual; System altered. SQL> alter system set result_cache_max_result=50; System altered. SQL> show parameter result_cache NAME TYPE VALUE ------------------------------------ ----------- ------------------------------ client_result_cache_lag big integer 3000 client_result_cache_size big integer 0 result_cache_max_result integer 50 result_cache_max_size big integer 20M result_cache_mode string MANUAL result_cache_remote_expiration integer 0 SQL>
那么启用result cache 与不启用的效果在那呢?如下测试见证分晓!
eg:
SQL> set autotrace trace SQL> select count(*) from rhys.amy; Execution Plan ---------------------------------------------------------- Plan hash value: 2204613761 ------------------------------------------------------------------- | Id | Operation | Name | Rows | Cost (%CPU)| Time | ------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1 | 348 (1)| 00:00:05 | | 1 | SORT AGGREGATE | | 1 | | | | 2 | TABLE ACCESS FULL| AMY | 87260 | 348 (1)| 00:00:05 | ------------------------------------------------------------------- Statistics ---------------------------------------------------------- 61 recursive calls 0 db block gets 1271 consistent gets 1246 physical reads 0 redo size 528 bytes sent via SQL*Net to client 523 bytes received via SQL*Net from client 2 SQL*Net roundtrips to/from client 5 sorts (memory) 0 sorts (disk) 1 rows processed SQL> r 1* select count(*) from rhys.amy Execution Plan ---------------------------------------------------------- Plan hash value: 2204613761 ------------------------------------------------------------------- | Id | Operation | Name | Rows | Cost (%CPU)| Time | ------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1 | 348 (1)| 00:00:05 | | 1 | SORT AGGREGATE | | 1 | | | | 2 | TABLE ACCESS FULL| AMY | 87260 | 348 (1)| 00:00:05 | ------------------------------------------------------------------- Statistics ---------------------------------------------------------- 0 recursive calls 0 db block gets 1248 consistent gets 1246 physical reads 0 redo size 528 bytes sent via SQL*Net to client 523 bytes received via SQL*Net from client 2 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 1 rows processed SQL> r 1* select count(*) from rhys.amy Execution Plan ---------------------------------------------------------- Plan hash value: 2204613761 ------------------------------------------------------------------- | Id | Operation | Name | Rows | Cost (%CPU)| Time | ------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1 | 348 (1)| 00:00:05 | | 1 | SORT AGGREGATE | | 1 | | | | 2 | TABLE ACCESS FULL| AMY | 87260 | 348 (1)| 00:00:05 | ------------------------------------------------------------------- Statistics ---------------------------------------------------------- 0 recursive calls 0 db block gets 1248 consistent gets 1246 physical reads 0 redo size 528 bytes sent via SQL*Net to client 523 bytes received via SQL*Net from client 2 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 1 rows processed SQL> SQL> SQL>
首先看到查看rhys下的amy这张表在稳定下来的时候一致性读为1248,物理读为1246(万源之恶)。
现在使用result cache 功能。
SQL> select /*+result_cache*/ count(*) from rhys.amy; Execution Plan ---------------------------------------------------------- Plan hash value: 2204613761 ------------------------------------------------------------------------------------------ | Id | Operation | Name | Rows | Cost (%CPU)| Time | ------------------------------------------------------------------------------------------ | 0 | SELECT STATEMENT | | 1 | 348 (1)| 00:00:05 | | 1 | RESULT CACHE | 6tux55tbcpqfj66980yb24pfbh | | | | | 2 | SORT AGGREGATE | | 1 | | | | 3 | TABLE ACCESS FULL| AMY | 87260 | 348 (1)| 00:00:05 | ------------------------------------------------------------------------------------------ Result Cache Information (identified by operation id): ------------------------------------------------------ 1 - column-count=1; dependencies=(RHYS.AMY); attributes=(single-row); name="select /*+result_cache*/ count(*) from rhys.amy" Statistics ---------------------------------------------------------- 0 recursive calls 0 db block gets 1248 consistent gets 1246 physical reads 0 redo size 528 bytes sent via SQL*Net to client 523 bytes received via SQL*Net from client 2 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 1 rows processed
第一次执行该语句并将其缓存到result cache中,一致性读以及物理 读没有变化。
如下使用hints(result_cache)进行在此查询该结果集。如下:
SQL> select /*+result_cache*/ count(*) from rhys.amy; Execution Plan ---------------------------------------------------------- Plan hash value: 2204613761 ------------------------------------------------------------------------------------------ | Id | Operation | Name | Rows | Cost (%CPU)| Time | ------------------------------------------------------------------------------------------ | 0 | SELECT STATEMENT | | 1 | 348 (1)| 00:00:05 | | 1 | RESULT CACHE | 6tux55tbcpqfj66980yb24pfbh | | | | | 2 | SORT AGGREGATE | | 1 | | | | 3 | TABLE ACCESS FULL| AMY | 87260 | 348 (1)| 00:00:05 | ------------------------------------------------------------------------------------------ Result Cache Information (identified by operation id): ------------------------------------------------------ 1 - column-count=1; dependencies=(RHYS.AMY); attributes=(single-row); name="select /*+result_cache*/ count(*) from rhys.amy" Statistics ---------------------------------------------------------- 0 recursive calls 0 db block gets 0 consistent gets 0 physical reads 0 redo size 528 bytes sent via SQL*Net to client 523 bytes received via SQL*Net from client 2 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 1 rows processed SQL>
可见物理读和一致性读都没有了,直接获得了结果集。这是好事啊。呵呵。
对于mode为force模式演示如下:
SQL> alter system set result_cache_mode=force; System altered. SQL> SQL> set autotrace trace SQL> select count(*) from rhys.amy; Execution Plan ---------------------------------------------------------- Plan hash value: 2204613761 ------------------------------------------------------------------------------------------ | Id | Operation | Name | Rows | Cost (%CPU)| Time | ------------------------------------------------------------------------------------------ | 0 | SELECT STATEMENT | | 1 | 348 (1)| 00:00:05 | | 1 | RESULT CACHE | 6tux55tbcpqfj66980yb24pfbh | | | | | 2 | SORT AGGREGATE | | 1 | | | | 3 | TABLE ACCESS FULL| AMY | 87260 | 348 (1)| 00:00:05 | ------------------------------------------------------------------------------------------ Result Cache Information (identified by operation id): ------------------------------------------------------ 1 - column-count=1; dependencies=(RHYS.AMY); attributes=(single-row); name="select count(*) from rhys.amy" Statistics ---------------------------------------------------------- 63 recursive calls 8 db block gets 1327 consistent gets 1246 physical reads 0 redo size 528 bytes sent via SQL*Net to client 523 bytes received via SQL*Net from client 2 SQL*Net roundtrips to/from client 10 sorts (memory) 0 sorts (disk) 1 rows processed SQL> r 1* select count(*) from rhys.amy Execution Plan ---------------------------------------------------------- Plan hash value: 2204613761 ------------------------------------------------------------------------------------------ | Id | Operation | Name | Rows | Cost (%CPU)| Time | ------------------------------------------------------------------------------------------ | 0 | SELECT STATEMENT | | 1 | 348 (1)| 00:00:05 | | 1 | RESULT CACHE | 6tux55tbcpqfj66980yb24pfbh | | | | | 2 | SORT AGGREGATE | | 1 | | | | 3 | TABLE ACCESS FULL| AMY | 87260 | 348 (1)| 00:00:05 | ------------------------------------------------------------------------------------------ Result Cache Information (identified by operation id): ------------------------------------------------------ 1 - column-count=1; dependencies=(RHYS.AMY); attributes=(single-row); name="select count(*) from rhys.amy" Statistics ---------------------------------------------------------- 0 recursive calls 0 db block gets 0 consistent gets 0 physical reads 0 redo size 528 bytes sent via SQL*Net to client 523 bytes received via SQL*Net from client 2 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 1 rows processed SQL>
另外在联机手册中并没提及到result_cache_mode 存在auto模式,但是我在不经意输错的是否发现了这个值。
SQL> alter system set result_cache_mode=false;
alter system set result_cache_mode=false
*
ERROR at line 1:
ORA-00096: invalid value FALSE for parameter result_cache_mode, must be from amongFORCE, MANUAL, AUTO
查看资料发现auto,是只有使用hints的时候才能起作用,但是当再次查询结果的时候没必要在使用hints了,而是直接把结果取出来。测试如下:
SQL> set autotrace off SQL> execute dbms_result_cache.flush; PL/SQL procedure successfully completed. SQL> alter system set result_cache_mode=auto; System altered. SQL> set autotrace trace SQL> select /*+result_cache*/ count(*) from rhys.amy; Execution Plan ---------------------------------------------------------- Plan hash value: 2204613761 ------------------------------------------------------------------------------------------ | Id | Operation | Name | Rows | Cost (%CPU)| Time | ------------------------------------------------------------------------------------------ | 0 | SELECT STATEMENT | | 1 | 348 (1)| 00:00:05 | | 1 | RESULT CACHE | 6tux55tbcpqfj66980yb24pfbh | | | | | 2 | SORT AGGREGATE | | 1 | | | | 3 | TABLE ACCESS FULL| AMY | 87260 | 348 (1)| 00:00:05 | ------------------------------------------------------------------------------------------ Result Cache Information (identified by operation id): ------------------------------------------------------ 1 - column-count=1; dependencies=(RHYS.AMY); attributes=(single-row); name="select /*+result_cache*/ count(*) from rhys.amy" Statistics ---------------------------------------------------------- 49 recursive calls 0 db block gets 1275 consistent gets 1246 physical reads 0 redo size 528 bytes sent via SQL*Net to client 523 bytes received via SQL*Net from client 2 SQL*Net roundtrips to/from client 5 sorts (memory) 0 sorts (disk) 1 rows processed SQL> r 1* select /*+result_cache*/ count(*) from rhys.amy Execution Plan ---------------------------------------------------------- Plan hash value: 2204613761 ------------------------------------------------------------------------------------------ | Id | Operation | Name | Rows | Cost (%CPU)| Time | ------------------------------------------------------------------------------------------ | 0 | SELECT STATEMENT | | 1 | 348 (1)| 00:00:05 | | 1 | RESULT CACHE | 6tux55tbcpqfj66980yb24pfbh | | | | | 2 | SORT AGGREGATE | | 1 | | | | 3 | TABLE ACCESS FULL| AMY | 87260 | 348 (1)| 00:00:05 | ------------------------------------------------------------------------------------------ Result Cache Information (identified by operation id): ------------------------------------------------------ 1 - column-count=1; dependencies=(RHYS.AMY); attributes=(single-row); name="select /*+result_cache*/ count(*) from rhys.amy" Statistics ---------------------------------------------------------- 0 recursive calls 0 db block gets 0 consistent gets 0 physical reads 0 redo size 528 bytes sent via SQL*Net to client 523 bytes received via SQL*Net from client 2 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 1 rows processed
二、
result cache 管理
对于11g中新增了result cache 那么也新增了4个视图以及一个包。
相关视图如下:
就不在介绍了,可以参考联机手册进行分析以及学习:
http://www.oracle.com/pls/db112/search?word=v$result_cache_
现在看一个dbms_result_cache包:
存在有6个subprograms,
Subprogram | Description |
---|---|
Sets the bypass mode for the Result Cache |
|
Attempts to remove all the objects from the Result Cache, and depending on the arguments retains or releases the memory and retains or clears the statistics |
|
Invalidates all the result-set objects that dependent upon the specified dependency object |
|
Invalidates the specified result-set object(s) |
|
Produces the memory usage report for the Result Cache |
|
Checks the status of the Result Cache |
演示二个:
其他参考:
http://docs.oracle.com/cd/E11882_01/appdev.112/e40758/d_result_cache.htm#CHDJCFJG
SQL> set serveroutput on SQL> execute 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 = 20M bytes (20K blocks) Maximum Result Size = 10M bytes (10K blocks) [Memory] Total Memory = 168264 bytes [0.134% of the Shared Pool] ... Fixed Memory = 5352 bytes [0.004% of the Shared Pool] ... Dynamic Memory = 162912 bytes [0.129% of the Shared Pool] ....... Overhead = 130144 bytes ....... Cache Memory = 32K bytes (32 blocks) ........... Unused Memory = 30 blocks ........... Used Memory = 2 blocks ............... Dependencies = 1 blocks (1 count) ............... Results = 1 blocks ................... SQL = 1 blocks (1 count) PL/SQL procedure successfully completed. SQL> execute dbms_result_cache.memory_report(true); 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 = 20M bytes (20K blocks) Maximum Result Size = 10M bytes (10K blocks) [Memory] Total Memory = 168264 bytes [0.134% of the Shared Pool] ... Fixed Memory = 5352 bytes [0.004% of the Shared Pool] ....... Memory Mgr = 200 bytes ....... Cache Mgr = 208 bytes ....... Bloom Fltr = 2K bytes ....... State Objs = 2896 bytes ... Dynamic Memory = 162912 bytes [0.129% of the Shared Pool] ....... Overhead = 130144 bytes ........... Hash Table = 64K bytes (4K buckets) ........... Chunk Ptrs = 24K bytes (3K slots) ........... Chunk Maps = 12K bytes ........... Miscellaneous = 130144 bytes ....... Cache Memory = 32K bytes (32 blocks) ........... Unused Memory = 30 blocks ........... Used Memory = 2 blocks ............... Dependencies = 1 blocks (1 count) ............... Results = 1 blocks ................... SQL = 1 blocks (1 count) PL/SQL procedure successfully completed.
SQL> execute dbms_result_cache.flush; PL/SQL procedure successfully completed. SQL> execute dbms_result_cache.memory_report(true); 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 = 0 bytes Maximum Cache Size = 0 bytes (0 blocks) Maximum Result Size = 0 bytes (0 blocks) [Memory] Total Memory = 5352 bytes [0.004% of the Shared Pool] ... Fixed Memory = 5352 bytes [0.004% of the Shared Pool] ....... Memory Mgr = 200 bytes ....... Cache Mgr = 208 bytes ....... Bloom Fltr = 2K bytes ....... State Objs = 2896 bytes ... Dynamic Memory = 0 bytes [0.000% of the Shared Pool] PL/SQL procedure successfully completed. SQL>