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這篇文章主要介紹“sql語句執行緩慢的原因分析”，在日常操作中，相信很多人在sql語句執行緩慢的原因分析問題上存在疑惑，小編查閱了各式資料，整理出簡單好用的操作方法，希望對大家解答”sql語句執行緩慢的原因分析”的疑惑有所幫助！接下來，請跟著小編一起來學習吧！
1.環境:
zzzzzz> @ ver1
PORT_STRING VERSION BANNER
------------------------------ -------------- --------------------------------------------------------------------------------
x86_64/Linux 2.4.xx 11.2.0.3.0 Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production
2.執行腳本如下:
$ cat a.txt
SELECT /*+ &&2 */ owner,
index_name,
-- index_type,
table_NAME,
COMPRESSION,
UNIQUENESS,
distinct_keys,
AVG_LEAF_blocks_per_key,
AVG_DATA_BLOCKS_PER_KEY,
blevel,
leaf_blocks,
clustering_factor,
status,
num_rows,
sample_size,
last_analyzed
FROM dba_indexes
WHERE owner LIKE 'XXXXXX_YYY'
AND table_name = UPPER ('&&1')
AND (owner, index_name) IN (SELECT owner, index_name
FROM dba_indexes
WHERE owner LIKE 'XXXXXX_YYY'
AND index_type <> 'LOB'
MINUS
(SELECT object_owner, object_name
FROM v$sql_plan
WHERE object_type = 'INDEX'
AND object_owner LIKE 'XXXXXX_YYY'
UNION
SELECT object_owner, object_name
FROM dba_hist_sql_plan
WHERE object_type = 'INDEX'
AND object_owner LIKE 'XXXXXX_YYY')
MINUS
(SELECT owner, constraint_name
FROM dba_constraints
WHERE owner LIKE 'XXXXXX_YYY'
AND constraint_type IN ('P',
'U',
'R')));
--//主要目的先排除一些現在使用的索引.
3.執行:
--//session 1:
zzzzzz> alter session set statistics_level=all;
Session altered.
zzzzzz> @ a.txt MS_CF01 aaa
...
--//慢.等。。。。
--//session 1,按ctrl+c中斷執行,實際上沒有執行完成:
zzzzzz> @ dpc '' ''
PLAN_TABLE_OUTPUT
-------------------------------------
SQL_ID frzb5c8tjx9wz, child number 0
...
Plan hash value: 2331593202
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows |E-Bytes| Cost (%CPU)| E-Time | A-Rows | A-Time | Buffers | Reads | OMem | 1Mem | Used-Mem |
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | | 485 (100)| | 1 |00:01:42.24 | 2568K| 93 | | | |
| 1 | NESTED LOOPS OUTER | | 1 | 1 | 179 | 145 (0)| 00:00:02 | 1 |00:01:42.24 | 2568K| 93 | | | |
| 2 | NESTED LOOPS OUTER | | 1 | 1 | 168 | 144 (0)| 00:00:02 | 1 |00:01:42.24 | 2568K| 93 | | | |
| 3 | NESTED LOOPS OUTER | | 1 | 1 | 165 | 143 (0)| 00:00:02 | 1 |00:01:42.24 | 2568K| 93 | | | |
... 太長...
| 38 | SORT UNIQUE | | 3490 | 1 | 375 | 340 (97)| 00:00:05 | 126 |00:03:18.78 | 4909K| 15 | 2048 | 2048 | |
| 39 | UNION-ALL | | 3490 | | | | | 1461 |00:03:18.73 | 4909K| 15 | | | |
|* 40 | FIXED TABLE FULL | X$KQLFXPL | 3490 | 1 | 22 | 3 (100)| 00:00:01 | 826 |00:02:58.63 | 0 | 0 | | | |
|* 41 | TABLE ACCESS FULL | WRH$_SQL_PLAN | 3489 | 1 | 17 | 308 (1)| 00:00:04 | 635 |00:00:20.08 | 4909K| 15 | | | |
--//很明顯主要慢在ID=40,41,而實際上主要是循環次數3490導致執行緩慢.
--//很奇怪的是我在toad下很快完成.第1次執行需要實際長一點外,以后都很快.再次查看執行計劃
--//注不能在toad下看,toad看僅僅看到child_number=0的執行計劃.
zzzzzz> @ dpc frzb5c8tjx9wz ''
....
SQL_ID frzb5c8tjx9wz, child number 1
-------------------------------------
Plan hash value: 1956464785
---------------------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | E-Rows |E-Bytes| Cost (%CPU)| E-Time | OMem | 1Mem | Used-Mem |
---------------------------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | | | 570 (100)| | | | |
|* 1 | FILTER | | | | | | | | |
| 2 | NESTED LOOPS OUTER | | 1 | 179 | 230 (0)| 00:00:03 | | | |
| 3 | NESTED LOOPS OUTER | | 1 | 168 | 229 (0)| 00:00:03 | | | |
| 4 | NESTED LOOPS OUTER | | 1 | 164 | 228 (0)| 00:00:03 | | | |
| 5 | NESTED LOOPS | | 1 | 156 | 227 (0)| 00:00:03 | | | |
....
| 50 | UNION-ALL | | | | | | | | |
|* 51 | FIXED TABLE FULL | X$KQLFXPL | 1 | 22 | 3 (100)| 00:00:01 | | | |
|* 52 | TABLE ACCESS FULL | WRH$_SQL_PLAN | 1 | 17 | 308 (1)| 00:00:04 | | | |
| 53 | SORT UNIQUE NOSORT | | 1 | 211 | 15 (7)| 00:00:01 | | | |
--//開始想是正常的,因為我在sqlplus下設置了alter session set statistics_level=all;.但是仔細看仔細計劃對于的操作id不一樣,而且Plan hash value也不同.
--//我也嘗試在toad下加入alter session set statistics_level=all;按F9執行也會執行緩慢.
zzzzzz> @ share frzb5c8tjx9wz
SQL_TEXT = SELECT /*+ aaa */ owner, index_name, -- index_type, table_NAME, COMPRESSION, UNIQUENESS, distinct_keys, AVG_LEAF_blocks_per_key, AVG_DATA_BLOCKS_PER_KEY,
blevel, leaf_blocks, clustering_factor, status, num_rows, sample_size, last_analyzed FROM dba_indexes WHERE owner LIKE :"SYS_B_00" AND table_name = UPPER (:"SYS_B_01") AND (owner,
index_name) IN (SELECT owner, index_name FROM dba_indexes WHERE owner LIKE :"SYS_B_02" AND index_type <> :"SYS_B_03"
MINUS (SELECT object_owner, object_name FROM v$sql_plan WHERE object_type = :"SYS_B_04" AND
object_owner LIK
SQL_ID = frzb5c8tjx9wz
ADDRESS = 00000000AA459A38
CHILD_ADDRESS = 00000000AB1E7238
CHILD_NUMBER = 0
REASON = <ChildNode><ChildNumber>0</ChildNumber><ID>45</ID><reason>NLS
Settings(0)</reason><size>2x4</size><SessionLengthSemantics>0</SessionLengthSemantics><CursorLengthSemantics>0</CursorLengthSemantics></ChildNode><ChildNode><ChildNumber>0</ChildNumber><ID>3</ID><reason>Optimizer
mismatch(12)</reason><size>2x216</size><statistics_level> all typical </statistics_level></ChildNode>
--------------------------------------------------
SQL_TEXT = SELECT /*+ aaa */ owner, index_name, -- index_type, table_NAME, COMPRESSION, UNIQUENESS, distinct_keys, AVG_LEAF_blocks_per_key, AVG_DATA_BLOCKS_PER_KEY,
blevel, leaf_blocks, clustering_factor, status, num_rows, sample_size, last_analyzed FROM dba_indexes WHERE owner LIKE :"SYS_B_00" AND table_name = UPPER (:"SYS_B_01") AND (owner,
index_name) IN (SELECT owner, index_name FROM dba_indexes WHERE owner LIKE :"SYS_B_02" AND index_type <> :"SYS_B_03"
MINUS (SELECT object_owner, object_name FROM v$sql_plan WHERE object_type = :"SYS_B_04" AND
object_owner LIK
SQL_ID = frzb5c8tjx9wz
ADDRESS = 00000000AA459A38
CHILD_ADDRESS = 00000000AB3775D8
CHILD_NUMBER = 1
OPTIMIZER_MISMATCH = Y
REASON = <ChildNode><ChildNumber>1</ChildNumber><ID>3</ID><reason>Optimizer mismatch(12)</reason><size>2x216</size><statistics_level> typical all </statistics_level></ChildNode>
--//我發現一個奇特的情況,sqlplus執行的語句和toad下執行的語句不能共享,提示LANGUAGE_MISMATCH= Y.
zzzzzz> select sql_id,child_number,PLAN_HASH_VALUE,buffer_gets,executions,ELAPSED_TIME from v$sql where sql_id='frzb5c8tjx9wz';
SQL_ID CHILD_NUMBER PLAN_HASH_VALUE BUFFER_GETS EXECUTIONS ELAPSED_TIME
------------- ------------ --------------- ----------- ---------- ------------
frzb5c8tjx9wz 0 2331593202 4978087 1 201931031
frzb5c8tjx9wz 1 1956464785 30458 2 1486831
--//對比2者NLS*環境:
zzzzzz> select * from nls_session_parameters ;
PARAMETER VALUE
-------------------------- ----------------------------------
NLS_LANGUAGE AMERICAN
NLS_TERRITORY AMERICA
NLS_CURRENCY $
NLS_ISO_CURRENCY AMERICA
NLS_NUMERIC_CHARACTERS .,
NLS_CALENDAR GREGORIAN
NLS_DATE_FORMAT YYYY-MM-DD HH24:MI:SS
NLS_DATE_LANGUAGE AMERICAN
NLS_SORT BINARY
NLS_TIME_FORMAT HH.MI.SSXFF AM
NLS_TIMESTAMP_FORMAT YYYY-MM-DD HH24:MI:SS.FF
NLS_TIME_TZ_FORMAT HH24.MI.SSXFF TZH:TZM
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
NLS_TIMESTAMP_TZ_FORMAT YYYY-MM-DD HH24:MI:SS.FF TZH:TZM
NLS_DUAL_CURRENCY $
NLS_COMP BINARY
NLS_LENGTH_SEMANTICS BYTE
NLS_NCHAR_CONV_EXCP FALSE
17 rows selected.
--//toad下執行:
select * from nls_session_parameters ;
PARAMETER,VALUE
NLS_LANGUAGE,AMERICAN
NLS_TERRITORY,AMERICA
NLS_CURRENCY,$
NLS_ISO_CURRENCY,AMERICA
NLS_NUMERIC_CHARACTERS,.,
NLS_CALENDAR,GREGORIAN
NLS_DATE_FORMAT,YYYY-MM-DD HH24:MI:SS
NLS_DATE_LANGUAGE,AMERICAN
NLS_SORT,BINARY
NLS_TIME_FORMAT,HH.MI.SSXFF AM
NLS_TIMESTAMP_FORMAT,YYYY-MM-DD HH24:MI:SS.FF
NLS_TIME_TZ_FORMAT,HH.MI.SSXFF AM TZR
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
NLS_TIMESTAMP_TZ_FORMAT,YYYY-MM-DD HH24:MI:SS.FF TZH:TZM
NLS_DUAL_CURRENCY,$
NLS_COMP,BINARY
NLS_LENGTH_SEMANTICS,BYTE
NLS_NCHAR_CONV_EXCP,FALSE
--//注意下劃線,僅僅參數NLS_TIME_TZ_FORMAT不同.
$ export NLS_TIME_TZ_FORMAT='HH.MI.SSXFF AM TZR'
--//再次登錄,問題消失.
alter session set statistics_level=all;
@ a.txt MS_CF01 aaa
--//很慢.登錄后執行:
@ a.txt MS_CF01 aaa
--//可以發現很快,因為我在toad下已經執行過一次.
--//真心想不到這個參數,會導致這么奇怪的問題.
--//補充說明一下:
--//如果寫成'HH24.MI.SSXFF AM TZR',調用sqlplus報錯.
$ export NLS_TIME_TZ_FORMAT='HH24.MI.SSXFF AM TZR'
$ rlsql system/test12@192.168.31.8:1521/hrp430
ERROR:
ORA-01818: 'HH24' precludes use of meridian indicator
SP2-0152: ORACLE may not be functioning properly
ORA-24550: signal received: [si_signo=11] [si_errno=0] [si_code=1] [si_int=0] [si_ptr=(nil)] [si_addr=0x10]
kpedbg_dmp_stack()+362<-kpeDbgCrash()+192<-kpeDbgSignalHandler()+119<-skgesig_sigactionHandler()+218<-__sighandler()<-pthread_mutex_destroy()<-kpufhndl0()+5461<-kpufhndl()+11<-OCIHandleFree()+19<-afioci()+2372<-aficnthdf()+62<-aficexf()+185<-aficex()+370<-afidrv()+321<-frame_dummy()+123<-__libc_start_main()+244
rlwrap: warning: sqlplus crashed, killed by SIGSEGV.
rlwrap itself has not crashed, but for transparency,
it will now kill itself (without dumping core) with the same signal
warnings can be silenced by the --no-warnings (-n) option
Segmentation fault
--//多次嘗試,確認實際上這個問題并不是參數NLS_TIME_TZ_FORMAT導致問題,而是執行計劃不穩定.每次分析都有可能導致新的執行計劃.
--//參數NLS_TIME_TZ_FORMAT不同,僅僅導致產生新的子光標,重新生成的執行計劃.兩者混合在一起導致問題非常怪異.
--//包括設置alter session set statistics_level=all;
--//如果我改寫成如下,無論什么情況都是很快完成.
WITH a
AS (SELECT /*+ MATERIALIZE */ object_owner, object_name
FROM v$sql_plan
WHERE object_type = 'INDEX' AND object_owner LIKE 'XXXXXX_YYY')
SELECT /*+ &&2 */ owner
,index_name
,--index_type,
table_NAME
,COMPRESSION
,UNIQUENESS
,distinct_keys
,AVG_LEAF_blocks_per_key
,AVG_DATA_BLOCKS_PER_KEY
,blevel
,leaf_blocks
,clustering_factor
,status
,num_rows
,sample_size
,last_analyzed
FROM dba_indexes
WHERE owner LIKE 'XXXXXX_YYY'
AND table_name = UPPER ('&&1')
AND (owner, index_name) IN (SELECT owner, index_name
FROM dba_indexes
WHERE owner LIKE 'XXXXXX_YYY'
AND index_type <> 'LOB'
MINUS
(SELECT object_owner, object_name FROM a
UNION
SELECT object_owner, object_name
FROM dba_hist_sql_plan
WHERE object_type = 'INDEX'
AND object_owner LIKE 'XXXXXX_YYY')
MINUS
(SELECT owner, constraint_name
FROM dba_constraints
WHERE owner LIKE 'XXXXXX_YYY'
AND constraint_type IN ('P'
,'U'
,'R')));
zzzzzz> @ aaa.txt MS_CF01 aaa
zzzzzz> select sql_id,child_number,PLAN_HASH_VALUE,buffer_gets,executions,ELAPSED_TIME from v$sql where sql_id='4zapbf2u32kx2';
SQL_ID CHILD_NUMBER PLAN_HASH_VALUE BUFFER_GETS EXECUTIONS ELAPSED_TIME
------------- ------------ --------------- ----------- ---------- ------------
4zapbf2u32kx2 0 2384590172 9680 1 903877
4zapbf2u32kx2 1 115948183 11455 1 847278
zzzzzz> @ share 4zapbf2u32kx2
SQL_TEXT = with a as ( SELECT /*+ MATERIALIZE */ object_owner, object_name FROM v$sql_plan WHERE object_type = :"SYS_B_00" AND object_owner LIKE :"SYS_B_01" ) SELECT /*+ aaa */ owner, index_name, --index_type,
table_NAME, COMPRESSION, UNIQUENESS, distinct_keys, AVG_LEAF_blocks_per_key, AVG_DATA_BLOCKS_PER_KEY, blevel, leaf_blocks, clustering_factor, status, num_rows, sample_size,
last_analyzed FROM dba_indexes WHERE owner LIKE :"SYS_B_02" AND table_name = UPPER (:"SYS_B_03") AND (owner, index_name) IN (SELECT owner, index_name FROM dba_indexes
WHERE owner LIKE :"SYS_B_04" AND index_type <> :"SYS_B_05" MINUS (SELECT object_owner, object_name FROM a
UN
SQL_ID = 4zapbf2u32kx2
ADDRESS = 00000000A6303098
CHILD_ADDRESS = 00000000A68317F8
CHILD_NUMBER = 0
USE_FEEDBACK_STATS = Y
REASON = <ChildNode><ChildNumber>0</ChildNumber><ID>3</ID><reason>Optimizer mismatch(13)</reason><size>3x4</size><kxscflg>32</kxscflg><kxscfl4>4194560</kxscfl4><dnum_kksfcxe>262144</dnum_kksfcxe></ChildNode>
--------------------------------------------------
SQL_TEXT = with a as ( SELECT /*+ MATERIALIZE */ object_owner, object_name FROM v$sql_plan WHERE object_type = :"SYS_B_00" AND object_owner LIKE :"SYS_B_01" ) SELECT /*+ aaa */ owner, index_name, --index_type,
table_NAME, COMPRESSION, UNIQUENESS, distinct_keys, AVG_LEAF_blocks_per_key, AVG_DATA_BLOCKS_PER_KEY, blevel, leaf_blocks, clustering_factor, status, num_rows, sample_size,
last_analyzed FROM dba_indexes WHERE owner LIKE :"SYS_B_02" AND table_name = UPPER (:"SYS_B_03") AND (owner, index_name) IN (SELECT owner, index_name FROM dba_indexes
WHERE owner LIKE :"SYS_B_04" AND index_type <> :"SYS_B_05" MINUS (SELECT object_owner, object_name FROM a
UN
SQL_ID = 4zapbf2u32kx2
ADDRESS = 00000000A6303098
CHILD_ADDRESS = 00000000A841E528
CHILD_NUMBER = 1
REASON =
--------------------------------------------------
PL/SQL procedure successfully completed.
--//不過不能共享的原因是是USE_FEEDBACK_STATS=Y.
總結:
1.環境變量,執行時參數不同導致產生新的子光標,出現一些怪異的情況,感覺toad下執行快,而sqlplus下執行慢.實際上反過來的情況也出
現過.我估計cardinality FEEDBACK的影響.
2.對于復雜視圖的執行計劃先 MATERIALIZE也許能獲得好的效果.
3.我發現一個奇怪的情況就是實際上打開alter session set statistics_level=all;就會選擇慢的執行計劃.
--//sqlplus開始第1次執行(硬分析)總是選擇慢的執行計劃.真心搞不懂....暫時放一下.
到此，關于“sql語句執行緩慢的原因分析”的學習就結束了，希望能夠解決大家的疑惑。理論與實踐的搭配能更好的幫助大家學習，快去試試吧！若想繼續學習更多相關知識，請繼續關注億速云網站，小編會繼續努力為大家帶來更多實用的文章！
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