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小y這個名字，是筆者臨時想的一個筆名，其實沒有什么特殊的含義，就暫且用他來代表我們這些為各個數據中心奉獻自己青春的一群默默無聞的IT人吧！
小y今天要和大家分享的是一個疑難雜癥的分析過程。如果大家有耐心讀完這個案例，一定會或多或少有些收獲，也就沒浪費小y的一片苦心。
具體來說是一個應用間歇性局部掛起案例的分析過程，報告中將對
Oracle
數據庫穩定運行的共性風險和隱患作出提醒。
據客戶反映，應用會間歇性出現異常，包括 insert 單條記錄在內的操作長時間無法完成，按照客戶的說法，數據庫內可能有“死鎖”現象，希望能夠找到問題發生的根因，提出解決方案，以避免問題再次發生。
2015 年 12 月 23 日，問題再次發生，客戶再次聯系到小 y， 小 y 通過遠程方式進行了信息收集和故障診斷，最終定位了問題的根本原因。
環境介紹：
|
操作系統 > > > > > > > |
INSERT INTO TABLE_NAME(COL1,COL2,COL3,COL4,COL5,COL6,COL7)VALUES(:1,:2,:3,:4,:5,:6,:7) |
> > > > > > > >
SQL> oradebug setmypid
Statement processed.
SQL> oradebug hanganalyze 3
Hang Analysis in /oracle/admin/xxdb/udump/xxdb_ora_14136.trc
SQL>
SQL> oradebug dump systemstate 266
Statement processed.
SQL> oradebug tracefile_name
/oracle/admin/xxdb/udump/xxdb_ora_14136.trc
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PROCESS 19:
----------------------------------------
SO: c00000003949b948, type: 2, owner: 0000000000000000, flag: INIT/-/-/0x00
(process) Oracle pid=19, calls cur/top: c0000000397209b0/c0000000397209b0, flag: (0) -
int error: 0, call error: 0, sess error: 0, txn error 0
(post info) last post received: 0 0 121
last post received-location: kcbzww
last process to post me: c000000039496148 1 22
last post sent: 0 0 121
last post sent-location: kcbzww
last process posted by me: c000000039496148 1 22
(latch info) wait_event=0 bits=0
Process Group: DEFAULT, pseudo proc: c000000039529928
O/S info: user: oracle, term: UNKNOWN, ospid: 11880
OSD pid info: Unix process pid: 11880, image: oracle@ap-machine-
*** 2015-12-22 10:34:53.431
Short stack dump:
ksdxfstk()+48<-ksdxcb()+1200<-sspuser()+368<-<kernel><-_
pw_wait()+48<-pw_wait()
+128<-sskgpwwait()+384<-skgpwwait()+208<-ksliwat()+1728<-kslwaitns_timed()+112<-kskthbwt()+400<-kslwait()+640<-ktugur()+4416<-ktuchg()+1280<-ktbchg2()+704<-kdiins0()+267536<-kdiinsp()+320<-kauxsin()+2960<-insidx()+1744<-insrow()+1440<-insdrv()+960<-inscovexe()+1408<-insExecStmtExecIniEngine()+176<-insexe()+1040<-opiexe()+13776<-kpoal8()+3808<-opiodr()+2144<-ttcpip()+1680<-opitsk()+2368<-opiino()+1664<-opiodr()+2144<-opidrv()+1248<-sou2o()+240<-opimai_real()+496<-main()+240<-main_opd_entry()+80
----------------------------------------
SO: c0000000396d80d8, type: 4, owner: c00000003949b948, flag: INIT/-/-/0x00
(session) sid: 315 trans: c0000000355b2a28, creator: c00000003949b948, flag: (100041) USR/- BSY/-/-/-/-/-
DID: 0001-0013-00000027, short-term DID: 0000-0000-00000000
txn branch: 0000000000000000
oct: 2, prv: 0, sql: c0000000384bad50, psql: c0000000384bad50, user: 33/XXDB
service name: xxdb
O/S info: user: , term: , ospid: 1234, machine: rvwapp2-1
program:
waiting for 'db file sequential read' wait_time=0, seconds since wait started=0
file#=c, block#=2f359, blocks=1
blocking sess=0x0000000000000000 seq=42271
Dumping Session Wait History
for 'undo segment extension' count=1 wait_time=2 min 45 sec
segment#=6, =0, =0
for 'buffer busy waits' count=1 wait_time=0.000009 sec
file#=2, block#=59, class#=1b
for 'SQL*Net message from client' count=1 wait_time=0.000087 sec
driver id=28444553, #bytes=1, =0
for 'SQL*Net message to client' count=1 wait_time=0.000001 sec
driver id=28444553, #bytes=1, =0
for 'SQL*Net message from client' count=1 wait_time=0.000086 sec
driver id=28444553, #bytes=1, =0
for 'SQL*Net message to client' count=1 wait_time=0.000001 sec
driver id=28444553, #bytes=1, =0
for 'SQL*Net message from client' count=1 wait_time=0.000086 sec
driver id=28444553, #bytes=1, =0
for 'SQL*Net message to client' count=1 wait_time=0.000001 sec
driver id=28444553, #bytes=1, =0
for 'SQL*Net message from client' count=1 wait_time=0.000087 sec
driver id=28444553, #bytes=1, =0
for 'SQL*Net message to client' count=1 wait_time=0.000001 sec
driver id=28444553, #bytes=1, =0
Sampled Session History of session 315 serial 4544
---------------------------------------------------
The sampled session history is constructed by sampling
the target session every 1 second. The sampling process
captures at each sample if the session is in a non-idle wait,
an idle wait, or not in a wait. If the session is in a
non-idle wait then one interval is shown for all the samples
the session was in the same non-idle wait. If the
session is in an idle wait or not in a wait for
consecutive samples then one interval is shown for all
the consecutive samples. Though we display these consecutive
samples in a single interval the session may NOT be continuously
idle or not in a wait (the sampling process does not know).
The history is displayed in reverse chronological order.
sample interval: 1 sec, max history 120 sec
---------------------------------------------------
[120 samples, 10:32:52 - 10:34:53]
waited for 'undo segment extension', seq_num: 42270
p1: 'segment#'=0x6
p2: ''=0x0
p3: ''=0x0
time_waited: >= 120 sec (still in wait)
---------------------------------------------------
Sampled Session History Summary:
longest_non_idle_wait: 'undo segment extension'
[120 samples, 10:32:52 - 10:34:53]
time_waited: >= 120 sec (still in wait)
可以看到：
進程在被
ORADEBUG
間接喚醒后，不再等待
undo segment extension,
而是做
”
PROCESS 8:
----------------------------------------
SO: c000000039496148, type: 2, owner: 0000000000000000, flag: INIT/-/-/0x00
(process) Oracle pid=8, calls cur/top: c00000003971e868/c00000003971e868, flag: (16) SYSTEM
int error: 0, call error: 0, sess error: 0, txn error 0
(post info) last post received: 0 0 121
last post received-location: kcbzww
last process to post me: c0000000394a0948 211 0
last post sent: 0 0 24
last post sent-location: ksasnd
last process posted by me: c000000039495148 1 6
(latch info) wait_event=0 bits=0
Process Group: DEFAULT, pseudo proc: c000000039529928
O/S info: user: oracle, term: UNKNOWN, ospid: 10072
OSD pid info: Unix process pid: 10072, image: oracle@ap-machine- (SMON)
Short stack dump:
ksdxfstk()+48<-ksdxcb()+1200<-sspuser()+368<-<kernel><-_pw_wait()+48<-pw_wait()+352<-sskgpwwait()+384<-skgpwwait()+208<-ksliwat()+1728<-kslwaitns_timed()+112<-kskthbwt()+400<-kslwait()+640<-ktmmon()+1168<-ktmSmonMain()+64<-ksbrdp()+2368<-opirip()+1184<-opidrv()+1184<-sou2o()+240<-opimai_real()+336<-main()+240<-main_opd_entry()+80
----------------------------------------
----------------------------------------
SO: c0000000396ead68, type: 4, owner: c000000039496148, flag: INIT/-/-/0x00
(session) sid: 329 trans: 0000000000000000, creator: c000000039496148, flag: (100051) USR/- BSY/-/-/-/-/-
DID: 0001-0008-00000002, short-term DID: 0000-0000-00000000
txn branch: 0000000000000000
oct: 0, prv: 0, sql: 0000000000000000, psql: 0000000000000000, user: 0/SYS
service name: SYS$BACKGROUND
waiting for 'smon timer' wait_time=0, seconds since wait started=3109
sleep time=12c, failed=0, =0
blocking sess=0x0000000000000000 seq=7382
Dumping Session Wait History
for 'smon timer' count=1 wait_time=4 min 53 sec
sleep time=12c, failed=0, =0
for 'smon timer' count=1 wait_time=4 min 53 sec
sleep time=12c, failed=0, =0
for 'smon timer' count=1 wait_time=4 min 11 sec
sleep time=12c, failed=0, =0
for 'smon timer' count=1 wait_time=4 min 53 sec
sleep time=12c, failed=0, =0
for 'smon timer' count=1 wait_time=4 min 53 sec
sleep time=12c, failed=0, =0
for 'smon timer' count=1 wait_time=4 min 53 sec
sleep time=12c, failed=0, =0
for 'smon timer' count=1 wait_time=4 min 53 sec
sleep time=12c, failed=0, =0
for 'smon timer' count=1 wait_time=4 min 53 sec
sleep time=12c, failed=0, =0
for 'smon timer' count=1 wait_time=4 min 53 sec
sleep time=12c, failed=0, =0
for 'smon timer' count=1 wait_time=4 min 53 sec
sleep time=12c, failed=0, =0
Sampled Session History of session 329 serial 1
可以看到，
SMON
進程在等“
SMON TIMER
”，即空閑等待。
這說明
SMON
沒有因為阻塞在異常的等待上，導致無法騰出時間來處理前臺進程發過來的
undo segment
擴展請求。
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操作系統
The problem is a defect in the pw_wait() O/S system call.
即
HPUX11.31
上，當安裝了
PHKL_37456
這個調度補丁后，操作系統調用
pw_wait
存在缺陷，導致進程無法從
post/wait
中被喚醒，解決方案是
Solution: on 11.31 install PHKL_38397 or later equivalent.
以下是官網原文
Processes Hang Waiting on 'cursor: pin S wait on X' (and other Wait Events) on HP-UX 11.23 and 11.31 Itanium Systems (Doc ID 580273.1)
In this Document
APPLIES TO:
Oracle Database - Enterprise Edition - Version 9.2.0.1 and later
cursor: pin S wait on X (10g wait)
kksfbc child completion
SGA: allocation forcing component growth
There is no blocker process.
0: c0000000003e2ff0 : pw_wait() + 0x30 (/usr/lib/hpux64/libc.so.1)
Workaround: oradebug setospid+unlimit to free the hanging process:
1.
Solution: on 11.31 install PHKL_38397 or later equivalent.
Solution: on 11.23 install PHKL_37809 or later equivalent.
Note: the patches whose names begin with PHKL_ are HP-UX patches. Please check with HP-UX support on the latest applicable patch numbers as such patches are regularly updated and superceded.
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INSERT INTO TABLE_NAME(COL1,COL2,COL3,COL4,COL5,COL6,COL7)VALUES(:1,:2,:3,:4,:5,:6,:7)
之所以執行不下去，不是因為死鎖，而是因為該會話即
SID=315
的會話
,
需要執行
DML
，因此需要
UNDO SEGMENT
即回滾段來存儲前鏡像，但發現回滾段空間不足，需要通知
SMON
后臺進程來完成擴展的請求
,
但是長時間沒有獲得回滾段擴展成功與否的返回消息。前臺進程和
SMON
之間通過
POST/WAIT
進制來通訊。
由于操作系統
HPUX
調度的缺陷，具體來說是
pw_wait
系統調用
(post/wait)
存在缺陷，當
SMON
進程完成回滾段擴展后，消息返回時，前臺進程
SID=315
并沒有能被及時調度到
CPU
上繼續處理后續工作，即體現出來就是等待在“
undo segment extension
“事件上等待，當我們人為使用
ORADEBUG
對
SID 315
收集信息并間接喚醒了該前臺進程后，前臺進行可以繼續往下工作，這更加印證了
SMON
已經將消息已經返回給前臺進程，只是由于操作系統調度進制的問題，未能即使將前臺進程調度到
CPU
上，拿到
UNDO
擴展成功的消息
造成該故障的根本原因是操作系統調度機制的問題，該問題命中操作系統
HPUX
上的已知缺陷。
The problem is a defect in the pw_wait() O/S system call.
即
HPUX11.31
上，當安裝了
PHKL_37456
這個調度補丁后，操作系統調用
pw_wait
存在缺陷，導致進程無法從
post/wait
中被喚醒，解決方案是
Solution: on 11.31 install PHKL_38397 or later equivalent.
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3.2 建議
Solution: on 11.31 install PHKL_38397 or later equivalent.
請系統管理員為操作系統安裝
PHKL_38397
補丁。
本文是轉載中亦安圖的文章。
On HP-UX 11.31, this is caused by a problem with the HP-UX scheduler patch PHKL_37456:
PHKL_37456 scheduler cumulative patch
HP-UX Itanium
***Checked for relevance on 23-JUL-2013***
The variety in wait events is explained by the fact that the underlying issue is with the pw_wait() HP-UX system call.
Therefore, the above list is not exhaustive, use the pstack output below to match the problem in all cases.
The problem is commonly seen on Parallel Execution Slave processes but can affect any Oracle process.
A command to generate a systemstate, processstate, or errorstack dump e.g. via ALTER SESSION or oradebug command frees the hanging process.
An example of the top of the call stack of an affected process, obtained using pstack:
1: 4000000002e98a20 : pw_wait() + 0x80
On HP-UX 11.31, this is caused by a problem with the HP-UX scheduler patch PHKL_37456:
PHKL_37456 scheduler cumulative patch
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