[20160121]调式PL SQL.txt
--一上班，看到一个帖子，里面提到一些技巧，才想起来许多东西视乎在忘记。
--链接 ：https://connormcdonald.wordpress.com/2016/01/20/problematic-sql-plsql-is-your-friend/
--我自己重复测试看看。
1.环境：
SCOTT@book> @&r/ver1
PORT_STRING VERSION BANNER
------------------------------ -------------- --------------------------------------------------------------------------------
x86_64/Linux 2.4.xx 11.2.0.4.0 Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
create or replace procedure P is
x int;
begin
--
-- this is my proc, and it has one very poor SQL
--
select count(*)
into x
from dba_views;
select count(*)
into x
from dba_tables;
select count(*)
into x
from dba_objects;
select count(*)
into x
from dba_objects, dba_objects;
end;
/
--要以上脚本正常执行，必须显式授权select权限。
SYS@book> GRANT SELECT ON SYS.dba_views TO SCOTT;
Grant succeeded.
SYS@book> GRANT SELECT ON SYS.dba_tables TO SCOTT;
Grant succeeded.
SYS@book> GRANT SELECT ON SYS.dba_objects TO SCOTT;
Grant succeeded.
2.测试：
SCOTT@book> @ &r/spid
SID SERIAL# SPID PID P_SERIAL# C50
---------- ---------- ------ ------- ---------- --------------------------------------------------
90 589 51753 32 216 alter system kill session '90,589' immediate;
SCOTT@book> exec p
--很慢....
--打开另外的会话。
SCOTT@book> select sid,username, sql_id from v$session where status = 'ACTIVE' and last_call_et > 10 and username is not null;
SID USERNAME SQL_ID
---------- -------------------- -------------
90 SCOTT ff35fbgz27513
SCOTT@book> @ &r/wait
P1RAW P2RAW P3RAW P1 P2 P3 SID SERIAL# SEQ# EVENT STATE WAIT_TIME_MICRO SECONDS_IN_WAIT
---------------- ---------------- ---------------- ---------- ---------- ---------- ---------- ---------- ---------- ---------------------------------------- ------------------- --------------- ---------------
0000000062657100 0000000000000001 00 1650815232 1 0 104 1031 53 SQL*Net message to client WAITED SHORT TIME 3 0
SCOTT@book> select p1raw,p2raw,p3raw,p1,p2,p3,sid,serial#,seq#,event,state,wait_time_micro,seconds_in_wait,status from v$session where sid=90 ;
P1RAW P2RAW P3RAW P1 P2 P3 SID SERIAL# SEQ# EVENT STATE WAIT_TIME_MICRO SECONDS_IN_WAIT STATUS
---------------- ---------------- ---------------- ---------- ---------- ---------- ---------- ---------- ---------- ---------------------------------------- ------------------- --------------- --------------- --------
0000000062657100 0000000000000001 00 1650815232 1 0 90 589 68 SQL*Net message from client WAITED KNOWN TIME 97590648 153 ACTIVE
--从这里看仅仅SQL*Net message from client，实际上后台执行那条sql语句。具有一定的欺骗性，自己以后要注意。
SCOTT@book> @ &r/sqlid ff35fbgz27513
old 1: select sql_id,to_char(replace(sql_fulltext,chr(13),'')) sqltext from v$sql where sql_id = '&&1' and rownum<=1
new 1: select sql_id,to_char(replace(sql_fulltext,chr(13),'')) sqltext from v$sql where sql_id = 'ff35fbgz27513' and rownum<=1
old 3: select sql_id,to_char(replace(sql_text,chr(13),'')) sqltext from dba_hist_sqltext where sql_id = '&&1' and rownum<=1
new 3: select sql_id,to_char(replace(sql_text,chr(13),'')) sqltext from dba_hist_sqltext where sql_id = 'ff35fbgz27513' and rownum<=1
SQL_ID SQLTEXT
------------- ----------------------------------------------
ff35fbgz27513 SELECT COUNT(*) FROM DBA_OBJECTS, DBA_OBJECTS
--可以找到这条sql语句。
SCOTT@book> select PROGRAM_ID, PROGRAM_LINE# from v$sql where sql_id = 'ff35fbgz27513';
PROGRAM_ID PROGRAM_LINE#
---------- -------------
89889 19
--通过这里可以知道在那个存储过程以及哪一行.
SCOTT@book> select * from dba_objects where object_id=89889;
OWNER OBJECT_NAME SUBOBJECT_ OBJECT_ID DATA_OBJECT_ID OBJECT_TYPE CREATED LAST_DDL_TIME TIMESTAMP STATUS T G S NAMESPACE EDITION_NAME
------ ----------- ---------- ---------- -------------- ------------------- ------------------- ------------------- ------------------- ------- - - - ---------- ------------
SCOTT P 89889 PROCEDURE 2016-01-21 08:46:24 2016-01-21 08:51:56 2016-01-21:08:51:56 VALID N N N 1
SCOTT@book> select * from dba_source where owner=user and name='P';
OWNER NAME TYPE LINE TEXT
------ ----- ---------- ---- --------------------------------------------------
SCOTT P PROCEDURE 1 procedure P is
SCOTT P PROCEDURE 2 x int;
SCOTT P PROCEDURE 3 begin
SCOTT P PROCEDURE 4 --
SCOTT P PROCEDURE 5 -- this is my proc, and it has one very poor SQL
SCOTT P PROCEDURE 6 --
SCOTT P PROCEDURE 7 select count(*)
SCOTT P PROCEDURE 8 into x
SCOTT P PROCEDURE 9 from dba_views;
SCOTT P PROCEDURE 10
SCOTT P PROCEDURE 11 select count(*)
SCOTT P PROCEDURE 12 into x
SCOTT P PROCEDURE 13 from dba_tables;
SCOTT P PROCEDURE 14
SCOTT P PROCEDURE 15 select count(*)
SCOTT P PROCEDURE 16 into x
SCOTT P PROCEDURE 17 from dba_objects;
SCOTT P PROCEDURE 18
SCOTT P PROCEDURE 19 select count(*)
SCOTT P PROCEDURE 20 into x
SCOTT P PROCEDURE 21 from dba_objects, dba_objects;
SCOTT P PROCEDURE 22
SCOTT P PROCEDURE 23 end;
23 rows selected.
--从以上的测试，都能对上。
3.如何优化那条sql语句呢？
--当然这种笛卡尔积本来不是优化的可能。不过我想起以前好像可以通过no_merge不融合来获得好的效果。上面的笛卡尔结果太大。效果不明显。
--换一个人视图看看。
SCOTT@book> set timing on
SCOTT@book> SELECT COUNT (*) FROM dba_tables a , dba_tables b;
COUNT(*)
----------
8294400
Elapsed: 00:00:26.30
SCOTT@book> SELECT /*+ NO_MERGE(A) NO_MERGE(B) */ COUNT (*) FROM dba_tables a , dba_tables b;
COUNT(*)
----------
8294400
Elapsed: 00:00:00.48
--如果没有使用别名a，b。
SCOTT@book> SELECT /*+ NO_MERGE(DBA_TABLES_0002@SEL$1) NO_MERGE(DBA_TABLES_0001@SEL$1) */ COUNT (*) FROM dba_tables , dba_tables ;
COUNT(*)
----------
8294400
Elapsed: 00:00:00.68
