[20221128]再談防水墻(視圖訪問性能問題).txt
1.環境:
SYS> @ 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
2.問題分析:
--//上個星期看了生產系統awr報表,發現一些問題.原來防水墻不斷呼叫執行如下:
begin :con := "TASSETACL"."QUERYACL"(:sn, :on); end;
--//該陳述句已經消失,我問了同事,據說升級過該產品,當時awr的記錄如下:
SQL ordered by Executions
%CPU - CPU Time as a percentage of Elapsed Time
%IO - User I/O Time as a percentage of Elapsed Time
Total Executions: 23,199,582
Captured SQL account for 34.2% of Total
Executions Rows Processed Rows per Exec Elapsed Time (s)%CPU %IO SQL Id SQL Module SQL Text
6,522,522 6,521,177 1.00 1,660.15 99.4 0 190q1sz3ywrd7 xxxxxx.eee begin :con := "TASSETACL".QUE...
2,228,287 2,228,115 1.00 107.98 99.5 0 g7ytdh9mxt1s0 xxxxxx.eee select count ( :"SYS_B_0" ) fr...
--//而現在變成了如下:
SQL ordered by Elapsed Time
Resources reported for PL/SQL code includes the resources used by all SQL statements called by the code.
為PL/SQL代碼報告的資源包括該代碼呼叫的所有SQL陳述句所使用的資源，
% Total DB Time is the Elapsed Time of the SQL statement divided into the Total Database Time multiplied by 100
%Total - Elapsed Time as a percentage of Total DB time
%CPU - CPU Time as a percentage of Elapsed Time
%IO - User I/O Time as a percentage of Elapsed Time
Captured SQL account for 65.1% of Total DB Time (s): 33,342
Captured PL/SQL account for 41.7% of Total DB Time (s): 33,342
Elapsed Time (s) Executions Elapsed Time per Exec (s) %Total %CPU %IO SQL Id SQL Module SQL Text
5,156.39 33,682 0.15 15.47 98.35 0.01 3pw59r6rkw9gb [email protected] (TNS V1- declare PRIVS_ERROR exception;...
5,153.22 33,683 0.15 15.46 98.34 0.01 0xwxau19hznj8 [email protected] (TNS V1- begin dbagent.try_login(); end...
5,089.67 134,713 0.04 15.26 98.34 0.00 8vmu6k690g87k [email protected] (TNS V1- SELECT UPPER(NVL(PROGRAM, 'nul...
--//原來的問題消失了,但是消耗的時間卻增加了,很明顯對方的產品沒有經過嚴格的測驗,就給用戶使用了.
--//取出sql陳述句,主要便于查看并且格式化如下:
SYS> @ sql_id 3pw59r6rkw9gb
--SQL_ID = 3pw59r6rkw9gb
declare
PRIVS_ERROR exception; --raise error,if rule exception,will trigger privs_error
pragma exception_init(PRIVS_ERROR, -1031);
begin
execute immediate 'begin dbagent.try_login(); end;';
exception
when PRIVS_ERROR then
raise;
when others then
rollback;
end dbagent_logon;;
--//注意后面多了1個分號,是我寫的腳本無法區分PL/SQL陳述句與sql陳述句造成的問題.
SYS> @sql_id 0xwxau19hznj8
--SQL_ID = 0xwxau19hznj8
begin dbagent.try_login(); end;;
SYS> @ sql_id 8vmu6k690g87k
--SQL_ID = 8vmu6k690g87k
SELECT UPPER (NVL (PROGRAM, 'null'))
,UPPER (MODULE)
,TYPE
,DECODE
(
NVL (INSTR (PROCESS, ':'), 0)
,0, NVL (PROCESS, 1234)
,SUBSTR (PROCESS, 1, INSTR (PROCESS, ':') - 1)
)
,OSUSER
,MACHINE
,SCHEMANAME
,USERNAME
,SERVICE_NAME
,SID
,SERIAL#
FROM SYS.V_$SESSION
WHERE SID = SYS_CONTEXT ('userenv', 'sid');
--//134713/33682 = 3.99955.平均執行3pw59r6rkw9gb1次,執行8vmu6k690g87k 4次.
--//可以看出呼叫順序3pw59r6rkw9gb,0xwxau19hznj8,8vmu6k690g87k 分別執行次數的比例是1:1:4.
--//很明顯開發沒有寫好程式代碼.僅僅需要呼叫1次8vmu6k690g87k就ok了.
--//如果修改代碼可以提高效率4倍. 僅僅需要5156/4 = 1289秒.但是我的問題并不再這里,細節很重要,為什么8vmu6k690g87k的執行有點
--//慢.再仔細看sql_id='8vmu6k690g87k'每次執行需要0.04秒=40ms(估計存在四舍五入問題,因為0.04*4=0.16),有點慢,因為where條件
--//查詢使用sid,不應該存在這么"慢"的情況.
--//開始以為都是Module=oraagent.bin執行的,后面我發現實際上幾乎全部模塊都存在相似呼叫,看代碼可以猜出是登陸資料庫時觸發器
--//呼叫執行的代碼.這時我突然想起我自己寫的登陸觸發器用于設定cursor_sharing=force也存在類似的呼叫v$session視圖的情況,很
--//明顯我寫的代碼呼叫次數應該也有33XXX次數.Elapsed Time至少應該 5089/4 = 1272秒,但是并沒有出現在awr報表中.另外我想到是
--//否因為select部分消耗cpu資源太多,我馬上否定我的猜測,因為僅僅回傳1行,無論如何不應該這么"慢".
--//當我看我寫的觸發器代碼馬上明白問題在那里.我是分開寫的,可以參考鏈接
--// http://blog.itpub.net/267265/viewspace-2768591/ => [20210418]查詢v$視圖問題.txt
--// connor-mcdonald.com/2021/04/12/better-performance-when-querying-the-v-views
3.繼續:
$ cat a.txt
SELECT UPPER (NVL (PROGRAM, 'null'))
,UPPER (MODULE)
,TYPE
,DECODE
(
NVL (INSTR (PROCESS, ':'), 0)
,0, NVL (PROCESS, 1234)
,SUBSTR (PROCESS, 1, INSTR (PROCESS, ':') - 1)
)
,OSUSER
,MACHINE
,SCHEMANAME
,USERNAME
,SERVICE_NAME
,SID
,SERIAL#
FROM SYS.V_$SESSION
WHERE SID = SYS_CONTEXT ('userenv', 'sid');
--//查看起對應的執行計劃:
SYS> @ sl all
alter session set statistics_level = all;
Session altered.
SYS> @ a.txt
SYS> @ dpc '' '' ''
PLAN_TABLE_OUTPUT
---------------------------
Plan hash value: 2422122865
---------------------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows |E-Bytes| Cost (%CPU)| A-Rows | A-Time | OMem | 1Mem | Used-Mem |
---------------------------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | | 1 (100)| 1 |00:00:00.02 | | | |
| 1 | MERGE JOIN CARTESIAN | | 1 | 1 | 62 | 0 (0)| 1 |00:00:00.02 | | | |
| 2 | NESTED LOOPS | | 1 | 1 | 12 | 0 (0)| 1 |00:00:00.01 | | | |
|* 3 | FIXED TABLE FULL | X$KSLWT | 1 | 1 | 8 | 0 (0)| 1 |00:00:00.01 | | | |
|* 4 | FIXED TABLE FIXED INDEX| X$KSLED (ind:2) | 1 | 1 | 4 | 0 (0)| 1 |00:00:00.01 | | | |
| 5 | BUFFER SORT | | 1 | 1 | 50 | 0 (0)| 1 |00:00:00.02 | 2048 | 2048 | 2048 (0)|
|* 6 | FIXED TABLE FULL | X$KSUSE | 1 | 1 | 50 | 0 (0)| 1 |00:00:00.02 | | | |
---------------------------------------------------------------------------------------------------------------------------------------------
Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------
1 - SEL$88122447
3 - SEL$88122447 / W@SEL$4
4 - SEL$88122447 / E@SEL$4
6 - SEL$88122447 / S@SEL$4
Predicate Information (identified by operation id):
---------------------------------------------------
3 - filter("W"."KSLWTSID"=TO_NUMBER(SYS_CONTEXT('userenv','sid')))
4 - filter("W"."KSLWTEVT"="E"."INDX")
6 - filter((BITAND("S"."KSSPAFLG",1)<>0 AND BITAND("S"."KSUSEFLG",1)<>0 AND "S"."INDX"=TO_NUMBER(SYS_CONTEXT('userenv','sid'))
AND "S"."INST_ID"=USERENV('INSTANCE')))
--//你可以發現ID=3,全表掃描X$KSLWT,而過濾條件是 filter("W"."KSLWTSID"=TO_NUMBER(SYS_CONTEXT('userenv','sid'))),也就是無法把
--//SYS_CONTEXT ('userenv', 'sid')當作常量處理.
--//而生產庫X$KSLWT 記錄的數量不是一般測驗環境的數量.我的測驗環境僅僅回傳24條.而生產系統回傳很多.
SYS> select count(*) from X$KSLWT;
COUNT(*)
----------
8793
--//訪問X$KSUSE也是出現類似的情況.
--//解決很簡單,分開寫:
--// Get user SID information
SELECT SYS_CONTEXT('userenv', 'sid') INTO v_sid FROM dual;
--// Get Program executable,OSUSER Details,Machine Details for this session
SELECT UPPER(NVL(PROGRAM, 'NULL')),
UPPER(MODULE),
DECODE(NVL(INSTR(PROCESS, ':'), 0), 0, NVL(PROCESS, 1234), SUBSTR(PROCESS, 1, INSTR(PROCESS, ':') - 1))
TYPE, OSUSER, MACHINE, SCHEMANAME, USERNAME, SERVICE_NAME, SID, SERIAL#
FROM SYS.V_$SESSION
where sid = v_sid;
SYS> SELECT SYS_CONTEXT('userenv', 'sid') FROM dual;
SYS_CONTEXT('USERENV','SID')
----------------------------
17017
$ cat a.txt
SELECT UPPER (NVL (PROGRAM, 'null'))
,UPPER (MODULE)
,TYPE
,DECODE
(
NVL (INSTR (PROCESS, ':'), 0)
,0, NVL (PROCESS, 1234)
,SUBSTR (PROCESS, 1, INSTR (PROCESS, ':') - 1)
)
,OSUSER
,MACHINE
,SCHEMANAME
,USERNAME
,SERVICE_NAME
,SID
,SERIAL#
FROM SYS.V_$SESSION
WHERE
SID= 17017
--SID = SYS_CONTEXT ('userenv', 'sid')
;
SYS> @a.txt
..
SYS> @ dpc '' '' ''
PLAN_TABLE_OUTPUT
-------------------------------------
SQL_ID gxdr0gq6nyums, child number 0
-------------------------------------
Plan hash value: 589956979
----------------------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows |E-Bytes| Cost (%CPU)| A-Rows | A-Time | OMem | 1Mem | Used-Mem |
----------------------------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | | 1 (100)| 1 |00:00:00.01 | | | |
| 1 | NESTED LOOPS | | 1 | 1 | 62 | 0 (0)| 1 |00:00:00.01 | | | |
| 2 | MERGE JOIN CARTESIAN | | 1 | 1 | 58 | 0 (0)| 1 |00:00:00.01 | | | |
|* 3 | FIXED TABLE FIXED INDEX | X$KSUSE (ind:1) | 1 | 1 | 50 | 0 (0)| 1 |00:00:00.01 | | | |
| 4 | BUFFER SORT | | 1 | 1 | 8 | 0 (0)| 1 |00:00:00.01 | 2048 | 2048 | 2048 (0)|
|* 5 | FIXED TABLE FIXED INDEX| X$KSLWT (ind:1) | 1 | 1 | 8 | 0 (0)| 1 |00:00:00.01 | | | |
|* 6 | FIXED TABLE FIXED INDEX | X$KSLED (ind:2) | 1 | 1 | 4 | 0 (0)| 1 |00:00:00.01 | | | |
----------------------------------------------------------------------------------------------------------------------------------------------
Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------
1 - SEL$88122447
3 - SEL$88122447 / S@SEL$4
5 - SEL$88122447 / W@SEL$4
6 - SEL$88122447 / E@SEL$4
Predicate Information (identified by operation id):
---------------------------------------------------
3 - filter(("S"."INDX"=17017 AND BITAND("S"."KSSPAFLG",1)<>0 AND BITAND("S"."KSUSEFLG",1)<>0 AND
"S"."INST_ID"=USERENV('INSTANCE')))
5 - filter("W"."KSLWTSID"=17017)
6 - filter("W"."KSLWTEVT"="E"."INDX")
--//connor-mcdonald.com 鏈接給出了另外的寫法,使用with+materialize提示:
$ cat b.txt
with mysid as ( select /*+ materialize */ userenv('SID') n from dual )
SELECT UPPER(NVL(PROGRAM, 'NULL')),
UPPER(MODULE),
DECODE(NVL(INSTR(PROCESS, ':'), 0), 0, NVL(PROCESS, 1234), SUBSTR(PROCESS, 1, INSTR(PROCESS, ':') - 1))
TYPE, OSUSER, MACHINE, SCHEMANAME, USERNAME, SERVICE_NAME, SID, SERIAL#
FROM SYS.V_$SESSION,mysid
WHERE SID = mysid.n;
SYS> @ b.txt
..
Plan hash value: 2230424401
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows |E-Bytes| Cost (%CPU)| E-Time | A-Rows | A-Time | Buffers | Reads | Writes | OMem | 1Mem | Used-Mem |
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | | 4 (100)| | 1 |00:00:00.03 | 15 | 1 | 1 | | | |
| 1 | TEMP TABLE TRANSFORMATION | | 1 | | | | | 1 |00:00:00.03 | 15 | 1 | 1 | | | |
| 2 | LOAD AS SELECT | | 1 | | | | | 0 |00:00:00.02 | 4 | 0 | 1 | 270K| 270K| 270K (0)|
| 3 | FAST DUAL | | 1 | 1 | | 2 (0)| 00:00:01 | 1 |00:00:00.01 | 0 | 0 | 0 | | | |
| 4 | NESTED LOOPS | | 1 | 1 | 75 | 2 (0)| 00:00:01 | 1 |00:00:00.01 | 5 | 1 | 0 | | | |
| 5 | NESTED LOOPS | | 1 | 1 | 71 | 2 (0)| 00:00:01 | 1 |00:00:00.01 | 5 | 1 | 0 | | | |
| 6 | NESTED LOOPS | | 1 | 1 | 63 | 2 (0)| 00:00:01 | 1 |00:00:00.01 | 5 | 1 | 0 | | | |
| 7 | VIEW | | 1 | 1 | 13 | 2 (0)| 00:00:01 | 1 |00:00:00.01 | 5 | 1 | 0 | | | |
| 8 | TABLE ACCESS STORAGE FULL| SYS_TEMP_0FD9D6D71_CF54F429 | 1 | 1 | 13 | 2 (0)| 00:00:01 | 1 |00:00:00.01 | 5 | 1 | 0 | 1025K| 1025K| |
|* 9 | FIXED TABLE FIXED INDEX | X$KSUSE (ind:1) | 1 | 1 | 50 | 0 (0)| | 1 |00:00:00.01 | 0 | 0 | 0 | | | |
|* 10 | FIXED TABLE FIXED INDEX | X$KSLWT (ind:1) | 1 | 1 | 8 | 0 (0)| | 1 |00:00:00.01 | 0 | 0 | 0 | | | |
|* 11 | FIXED TABLE FIXED INDEX | X$KSLED (ind:2) | 1 | 1 | 4 | 0 (0)| | 1 |00:00:00.01 | 0 | 0 | 0 | | | |
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------
1 - SEL$71D7A081
2 - SEL$1
3 - SEL$1 / DUAL@SEL$1
7 - SEL$D67CB2D2 / MYSID@SEL$2
8 - SEL$D67CB2D2 / T1@SEL$D67CB2D2
9 - SEL$71D7A081 / S@SEL$5
10 - SEL$71D7A081 / W@SEL$5
11 - SEL$71D7A081 / E@SEL$5
Predicate Information (identified by operation id):
---------------------------------------------------
9 - filter((BITAND("S"."KSSPAFLG",1)<>0 AND BITAND("S"."KSUSEFLG",1)<>0 AND "S"."INST_ID"=USERENV('INSTANCE') AND "S"."INDX"="MYSID"."N"))
10 - filter("S"."INDX"="W"."KSLWTSID")
11 - filter("W"."KSLWTEVT"="E"."INDX")
4.性能對比:
--//我在toad下測驗,多次執行觀察
--//呼叫b.txt 大約需要2Xms.
--//呼叫a.txt 大約需要5Xms.
--//有時候兩者差異不大,感覺這樣比較不行,沒有考慮網路的往返.另外寫一篇測驗該陳述句性能的blog.
--//注:我后面測驗with+materialize要產生redo日志,不建議在生產系統應用這樣的寫法,主要原因是執行頻率太高了,累積起來redo很大!!
5.為什么呼叫1次0xwxau19hznj8,執行4次8vmu6k690g87k.
--//我看了一下源代碼,源代碼這次沒有加密.
--//通過程序collect_app_info呼叫sql_id=8vmu6k690g87k
--//而try_login代碼通過4個函式分別取得對應值
--get login app name
function get_app_name return varchar2 is
begin
collect_app_info;
return l_appname;
end;
--get login app module name
function get_app_module_name return varchar2 is
begin
collect_app_info;
return l_module;
end;
--get login app type
function get_app_type return varchar2 is
begin
collect_app_info;
return l_type;
end;
--get app process number
function get_app_process return number is
begin
collect_app_info;
return l_process;
end;
--//這樣就很好決議為什么呼叫1次執行4次sql_id=8vmu6k690g87k.而實際上
procedure collect_app_info is
begin
if not app_info_collect_status then
select upper(nvl(program, 'null')),
upper(module),
type,
decode(nvl(instr(process, ':'), 0),
0,
nvl(process, 1234),
substr(process, 1, instr(process, ':') - 1)),
osuser,
machine,
SCHEMANAME,
USERNAME,
SERVICE_NAME,
sid,
serial#
into l_appname,
l_module,
l_type,
l_process,
l_osuser,
l_machine,
l_SCHEMANAME,
l_username,
l_service_name,
l_sid,
l_serial#
from sys.v_$session
where sid = sys_context('userenv', 'sid');
end if;
end;
--//已經賦值給對應變數,根本不需要再通過什么函式回傳對應值.直接使用對應變數應該可以,當然我沒有測驗.
--//最簡單修改:
procedure collect_app_info is
begin
if not app_info_collect_status then
select userenv('SID') into l_sid from dual;
select upper(nvl(program, 'null')),
upper(module),
type,
decode(nvl(instr(process, ':'), 0),
0,
nvl(process, 1234),
substr(process, 1, instr(process, ':') - 1)),
osuser,
machine,
SCHEMANAME,
USERNAME,
SERVICE_NAME,
sid,
serial#
into l_appname,
l_module,
l_type,
l_process,
l_osuser,
l_machine,
l_SCHEMANAME,
l_username,
l_service_name,
l_sid,
l_serial#
from sys.v_$session
where sid = l_sid;
end if;
end;
--//我的感覺可能分開寫效率更高!!因為使用with+materialize會生成一個臨時表,會產生日志,我還給測驗看看.
6.總結:
--//很明顯對方缺乏蠻力測驗就把產品做了升級,我曾經對乙方工程師講過類似的問題,盡量不要讓客戶先于你發現產品的問題,這樣是很
--//丟臉的事情.你內部測驗怎么犯錯都可以,客戶是看不見的,一旦你犯錯,對方先發現,對方會........
--//實際上只要大量用戶連接資料庫,該陳述句的問題才明顯的暴露出來.
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