注：转：http://shsnc2014.blog.163.com/blog/static/2403690822014102411217903/
当我们做数据库升级项目的时候，我们一般会去做性能回归测试，通俗一点来说，就是把10g生产库的语句拿到11g生产环境上运行，如果发现运行过程中,由于优化器、实例参数等改变导致执行计划变化，最终导致性能退化的语句，需要拿出来单独进行分析及验证。要做这个事情，首先我们需要把我们的10g上的语句给采集出来，采集方法分为以下几种方式。
- cursor cache
- awr snapshots
- awr baselines
- another sql tuning set
- 10046 trace file(11g+)
对于大型的生产库，我们一般采集的是方式是:游标还有awr snapshots的数据。为了能够完美的抓取到全部的SQL语句，我们往往需要一天对cursor cache进行多次采集。大部分建议是放在高峰期的时候采集，这么做主要是为了防止有些SQL还没被抓取到sqlset就从shared pool中purge出去了。在这个抓取的过程中，有一个困扰的问题就是literal sql的一些语句。举个例子如下：
select * from emp where empno=1456;
select * from emp where empno=1457;
select * from emp where empno=1458;
这三个SQL语句会先后被采集进来，每天都这样采集，会导致我们的SQLSET的结果集越来越大。正常情况下，一个大型的生产库的SQL语句也就几w条而已，但是如果你的硬解析非常多的话，可能在短短的几天，你采集的语句就会突破到100w条以上。然后在做后面SQLSET转换到中转表的这个过程，会执行相当长的时间，搞不好就报ORA-01555,导致运行一段时间后无法成功转换。我在这上面被坑了好几次。可能你会说，就100w的数据，Oracle应该很快转换出来的吧。这个我得解释一下。我们的中转表里面其实包含了好几个LOB字段和特殊TYPE类型。一旦数据量大了，可以说速度完全不行。正是基于这种原因，我们需要考虑一种方式，在采集的过程中进行去除重复的操作。
我们来举个例子说明下。
1.新建SQLSET
SQL> exec dbms_sqltune.CREATE_SQLSET('sqlset1');
PL/SQL procedure successfully completed.
SQL> select * from dba_sqlset;
ID NAME OWNER DESCRIPTION CREATED LAST_MODI STATEMENT_COUNT
---------- --------------- --------------- ------------------------------ --------- --------- ---------------
1 sqlset1 SYS 11-MAY-14 11-MAY-14 0
2.使用scott用户,执行几条语句，执行前先flush下shared pool
SQL> alter system flush shared_pool;
System altered. connect scott/tiger
select * from emp;
select * from emp where empno=1456;
select * from emp where empno=1457;
3.使用sys用户开始采集语句
DECLARE
mycur DBMS_SQLTUNE.SQLSET_CURSOR;
BEGIN
OPEN mycur FOR
SELECT value(P)
FROM TABLE(dbms_sqltune.select_cursor_cache('parsing_schema_name in (''SCOTT'')',
NULL,
NULL,
NULL,
NULL,
1,
NULL,
'ALL')) p;
dbms_sqltune.load_sqlset(sqlset_name => 'sqlset1',
populate_cursor => mycur,
load_option => 'MERGE');
CLOSE mycur;
END;
/ SQL> select * from dba_sqlset;
ID NAME OWNER DESCRIPTION CREATED LAST_MODI STATEMENT_COUNT
---------- --------------- --------------- ------------------------------ --------- --------- ---------------
1 sqlset1 SYS 11-MAY-14 11-MAY-14 9
4.查看采集结果
SQL> select sql_id,sql_text from DBA_SQLSET_STATEMENTS ;
SQL_ID SQL_TEXT
------------- --------------------------------------------------------------------------------
1srhq04p4x0zz SELECT /* OPT_DYN_SAMP */ /*+ ALL_ROWS IGNORE_WHERE_CLAUSE NO_PARALLEL(SAMPLESUB
38mhtu5pc7d07 select * from emp where empno=1456
7hys3h7ysgf9m SELECT ATTRIBUTE,SCOPE,NUMERIC_VALUE,CHAR_VALUE,DATE_VALUE FROM SYSTEM.PRODUCT_P
a2dk8bdn0ujx7 select * from emp
bc26hcc8td76f select * from emp where empno=1457
cw6vxf0kbz3v1 SELECT CHAR_VALUE FROM SYSTEM.PRODUCT_PRIVS WHERE (UPPER('SQL*Plus') LIKE UPPE
d6vwqbw6r2ffk SELECT USER FROM DUAL
dyk4dprp70d74 SELECT DECODE('A','A','1','2') FROM DUAL
g4y6nw3tts7cc BEGIN DBMS_APPLICATION_INFO.SET_MODULE(:1,NULL); END;
从这里我们可以观察到我们的三条语句都采集进来了。这里我们可以看到我们的literal sql，如果每天对游标采集好几次的话，我们的literal sql会越采集越多，导致SQLSET的结果集非常大。当SQL数量达到百万级别后，使得我们的转换非常慢。如何去重呢？我们看下这个DBA_SQLSET_STATEMENTS的结构。
SQL> desc DBA_SQLSET_STATEMENTS
Name Null? Type
------------------------------------------- -------- -----------------------------
SQLSET_NAME NOT NULL VARCHAR2(30)
SQLSET_OWNER VARCHAR2(30)
SQLSET_ID NOT NULL NUMBER
SQL_ID NOT NULL VARCHAR2(13)
FORCE_MATCHING_SIGNATURE NOT NULL NUMBER
SQL_TEXT CLOB
PARSING_SCHEMA_NAME VARCHAR2(30)
PARSING_SCHEMA_ID NUMBER
PLAN_HASH_VALUE NOT NULL NUMBER
BIND_DATA RAW(2000)
BINDS_CAPTURED CHAR(1)
MODULE VARCHAR2(64)
ACTION VARCHAR2(64)
ELAPSED_TIME NUMBER
CPU_TIME NUMBER
BUFFER_GETS NUMBER
DISK_READS NUMBER
DIRECT_WRITES NUMBER
ROWS_PROCESSED NUMBER
FETCHES NUMBER
EXECUTIONS NUMBER
END_OF_FETCH_COUNT NUMBER
OPTIMIZER_COST NUMBER
OPTIMIZER_ENV RAW(2000)
PRIORITY NUMBER
COMMAND_TYPE NUMBER
FIRST_LOAD_TIME VARCHAR2(19)
STAT_PERIOD NUMBER
ACTIVE_STAT_PERIOD NUMBER
OTHER CLOB
PLAN_TIMESTAMP DATE
SQL_SEQ NOT NULL NUMBER SQL> select sql_id,sql_text,FORCE_MATCHING_SIGNATURE from DBA_SQLSET_STATEMENTS;
SQL_ID SQL_TEXT FORCE_MATCHING_SIGNATURE
------------- -------------------------------------------------------------------------------- ---------------------------
1srhq04p4x0zz SELECT /* OPT_DYN_SAMP */ /*+ ALL_ROWS IGNORE_WHERE_CLAUSE NO_PARALLEL(SAMPLESUB 4094562552765466770
38mhtu5pc7d07 select * from emp where empno=1456 16946033956547040230
7hys3h7ysgf9m SELECT ATTRIBUTE,SCOPE,NUMERIC_VALUE,CHAR_VALUE,DATE_VALUE FROM SYSTEM.PRODUCT_P 10967007256268736959
a2dk8bdn0ujx7 select * from emp 7001777653489406494
bc26hcc8td76f select * from emp where empno=1457 16946033956547040230
cw6vxf0kbz3v1 SELECT CHAR_VALUE FROM SYSTEM.PRODUCT_PRIVS WHERE (UPPER('SQL*Plus') LIKE UPPE 18201431879876406267
d6vwqbw6r2ffk SELECT USER FROM DUAL 17376422952071979402
dyk4dprp70d74 SELECT DECODE('A','A','1','2') FROM DUAL 1846728577492307645
g4y6nw3tts7cc BEGIN DBMS_APPLICATION_INFO.SET_MODULE(:1,NULL); END; 0
这里我们主要利用FORCE_MATCHING_SIGNATURE这个字段。可以看到我们的literal sql的FORCE_MATCHING_SIGNATURE的值是相同的。这里是16946033956547040230。所以我们要对这个列进行distinct，并将distinct出来的值放在一个我们自定义的Table里面。
5.去重采集
SQL> create table spaqc as select distinct FORCE_MATCHING_SIGNATURE from DBA_SQLSET_STATEMENTS;
Table created. SQL> select * from spaqc;
FORCE_MATCHING_SIGNATURE
---------------------------
18201431879876406267
1846728577492307645
4094562552765466770
17376422952071979402
10967007256268736959
7001777653489406494
16946033956547040230
0
8 rows selected.
这里需要注意一下FORCE_MATCHING_SIGNATURE为0的情况下，一般是运行PL/SQL、JOB之类的操作，这个我们不能过滤掉。所以我们要把0这行给删掉。
SQL> delete from spaqc where FORCE_MATCHING_SIGNATURE=0;
1 row deleted. SQL> commit;
Commit complete.
6.再次测试，看看literal sql会不会被采集。
select * from emp where empno=1458;
select * from emp where empno=1459;
select * from emp where empno=1460;
select * from emp where empno=1460 and ENAME='scott'; DECLARE
mycur DBMS_SQLTUNE.SQLSET_CURSOR;
BEGIN
OPEN mycur FOR
SELECT value(P)
FROM TABLE(dbms_sqltune.select_cursor_cache('parsing_schema_name in (''SCOTT'') and FORCE_MATCHING_SIGNATURE not in (select FORCE_MATCHING_SIGNATURE from spaqc)',
NULL,
NULL,
NULL,
NULL,
1,
NULL,
'ALL')) p;
dbms_sqltune.load_sqlset(sqlset_name => 'sqlset1',
populate_cursor => mycur,
load_option => 'MERGE');
CLOSE mycur;
END;
/
SQL> select sql_id,sql_text,FORCE_MATCHING_SIGNATURE from DBA_SQLSET_STATEMENTS ;
SQL_ID SQL_TEXT FORCE_MATCHING_SIGNATURE
------------- -------------------------------------------------------------------------------- ---------------------------
1srhq04p4x0zz SELECT /* OPT_DYN_SAMP */ /*+ ALL_ROWS IGNORE_WHERE_CLAUSE NO_PARALLEL(SAMPLESUB 4094562552765466770
38mhtu5pc7d07 select * from emp where empno=1456 16946033956547040230
7hys3h7ysgf9m SELECT ATTRIBUTE,SCOPE,NUMERIC_VALUE,CHAR_VALUE,DATE_VALUE FROM SYSTEM.PRODUCT_P 10967007256268736959
a2dk8bdn0ujx7 select * from emp 7001777653489406494
bc26hcc8td76f select * from emp where empno=1457 16946033956547040230
cw6vxf0kbz3v1 SELECT CHAR_VALUE FROM SYSTEM.PRODUCT_PRIVS WHERE (UPPER('SQL*Plus') LIKE UPPE 18201431879876406267
d6vwqbw6r2ffk SELECT USER FROM DUAL 17376422952071979402
d8fw5smyjva0b select * from emp where empno=1460 and ENAME='scott' 17445701640293030006
dyk4dprp70d74 SELECT DECODE('A','A','1','2') FROM DUAL 1846728577492307645
g4y6nw3tts7cc BEGIN DBMS_APPLICATION_INFO.SET_MODULE(:1,NULL); END; 0 10 rows selected.
这里我们看到literal sql没有被采集进来，我们实现了游标采集的过滤。