在應(yīng)用中，我們經(jīng)常會(huì)碰到sql執(zhí)行很慢，但是數(shù)據(jù)庫(kù)cpu和內(nèi)存使用率又不高的情況，類似的問題基本上由于鎖，排序等原因造成，本文主要描述如何去定位鎖等待問題，誰(shuí)在鎖等待？等待誰(shuí)持有的鎖？鎖在那個(gè)表？

一、測(cè)試準(zhǔn)備

1、先在session1執(zhí)行如下操作，創(chuàng)建測(cè)試表

#db2 connect to eos

#export DB2OPTIONS=+C

#db2 'create table tacy_test (a int not null primary key,b varchar(10))'

#db2 'insert into tacy_test values(1,'a')'

#db2 'insert into tacy_test values(2,'a')'

#db2 'insert into tacy_test values(3,'a')'

#db2 'insert into tacy_test values(4,'a')'

#db2 commit

2、在session2執(zhí)行如下操作

#db2 connect to eos

#export DB2OPTIONS=+C

二、產(chǎn)生一個(gè)lock wait

在session1做一個(gè)表更新：

#db2 'update tacy_test set b='b' where a=4'

sql執(zhí)行成功

在session2做同樣更新操作：

#db2 'update tacy_test set b='c' where a=4'

進(jìn)程被掛起等待

三、定位鎖等待

1、先來(lái)看看應(yīng)用的情況：

#db2pd -db eos -applications

Database Partition 0 -- Database EOS -- Active -- Up 0 days 07:37:37

Applications:

Address AppHandl [nod-index] NumAgents CoorPid Status C-AnchID C-StmtUID L-AnchID L-StmtUID Appid

0x10140040 8 [000-00008] 1 8425 Lock-wait 80 2 66 1 *LOCAL.db2inst1.071124043739

0x100CE540 7 [000-00007] 1 8358 UOW-Waiting 0 0 80 2 *LOCAL.db2inst1.071124043708

可以看到有一個(gè)應(yīng)用的狀態(tài)處于Lock-wait

2、現(xiàn)在我們來(lái)看看應(yīng)用在等什么

#db2pd -db eos -locks showlock wait

Database Partition 0 -- Database EOS -- Active -- Up 0 days 07:42:56

Locks:

Address TranHdl Lockname Type Mode Sts Owner Dur HldCnt Att Rlse

0x2C8E0760 3 02001806078066020000000052 Row ..X W 2 1 0 0 0x0 TbspaceID 2 TableID 1560 RecordID 0x2668007

鎖的類型為Row（行鎖），X鎖（排他鎖），下面是我們最關(guān)心的鎖的位置

TbspaceID 2 TableID 1560 RecordID 0x2668007

其中TbspaceID為表空間ID，TableID為表的ID，RecordID代表具體位置，全部應(yīng)該是0x0266807,其中前面三個(gè)字節(jié)為page number，為0x02668，后面一個(gè)字節(jié)代表solt identifier，為0x07

3、找到相應(yīng)的表

#db2 'select tbspace,tabschema,tabname,tableid,tbspaceid from syscat.tables where tbspaceid=2 and tableid=1560'

TBSPACE TABSCHEMA TABNAME TABLEID TBSPACEID

------------ ----------- ---------- ------- ---------

USERSPACE1 DB2INST1 TACY_TEST 1560 2

1 record(s) selected.

4、根據(jù)RecordID找到鎖在哪行

db2提供了一個(gè)強(qiáng)大的數(shù)據(jù)分析工具db2dart，可以dump出相應(yīng)的page數(shù)據(jù)

#db2dart eos /dd /tsi 2 /oi 1560 /ps 157312p /np 1 /v y

Warning: The database state is not consistent.

Warning: Reorg rows MAY be due to the inconsistent state of the database.

DB2DART Processing completed with warning(s)!

Complete DB2DART report found in:

/home/db2inst1/sqllib/db2dump/DART0000/EOS.RPT

其中tsi為表空間id(2)，oi為表id(1560)，ps為page number(0x0266807)，需要轉(zhuǎn)換為十進(jìn)制，在結(jié)尾必須加p，np代表你要獲取的頁(yè)數(shù)，v為是否詳細(xì)輸出

現(xiàn)在我們來(lái)看看EOS.RPT

______________________________________________________________________________

_______ DART _______

D a t a b a s e A n a l y s i s a n d R e p o r t i n g T o o l

IBM DB2 6000

______________________________________________________________________________

DART (V8.1.0) Report:

2007-11-24-20.59.51.355893

Database Name: EOS

Report name: EOS.RPT

Old report back-up: EOS.BAK

Database Subdirectory: /opt/db2/db2inst1/NODE0000/SQL00001

Operational Mode: Database Inspection Only (INSPECT)

______________________________________________________________________________

------------------------------------------------------------------------------

Action option: DD

Table-object-ID: 1560; Tablespace-ID: 2; First-page: 157312p; Number-pages: 1; Verbose: y

Warning: The database state is not consistent.

Warning: Reorg rows MAY be due to the inconsistent state of the database.

Connecting to Buffer Pool Services...

Table object report phase start.

Dump format is verbose.

______________________________________

Page 0 of object 1560 from table space 2.

BPS Page Header:

Page Data Offset = 48

Page Data Length = 4048

Page LSN = 0000 AE97 AE41

Object Page Number = 0

Pool Page Number = 157312

Object ID = 1560

Object Type = Data Object

Data Page Header:

Slot Count = 8

Total Free Space = 2784

Total Reserve Space = 0

Youngest Reserve Space = n/a

Youngest TID = n/a

Free Space Offset = 2799

Maximum Record Size = 23

Data Records:

Slot 0:

Offset Location = 3996 (xF9C)

Record Length = 32 (x20)

Record Type = Data Object Header Control Record

Page count = 1

Object Creation LSN = 0000 AE97 800C

Object State = x0000

UDI Since Runstats = 0

DART Field = x00000000

Slot1:

Offset Location = 2992 (xBB0)

Record Length = 1004 (x3EC)

Record Type = Free Space Control Record

Free space entries:

0: 2884 (x0B44), 4028 (x0FBC), 4028 (x0FBC), 4028 (x0FBC)

4: 4028 (x0FBC), 4028 (x0FBC), 4028 (x0FBC), 4028 (x0FBC)

8: 4028 (x0FBC), 4028 (x0FBC), 4028 (x0FBC), 4028 (x0FBC)

省略。。。

492: 4028 (x0FBC), 4028 (x0FBC), 4028 (x0FBC), 4028 (x0FBC)

496: 4028 (x0FBC), 4028 (x0FBC), 4028 (x0FBC), 4028 (x0FBC)

Slot 2:

Offset Location = 2916 (xB64)

Record Length = 76 (x4C)

Record Type = Table Directory Record

MetaIndex Root Page = 157377

Index Type = 2

Table Descriptor Pointer -- Page 157312 Slot 3

Max Insert Search = 0

Flags = x02000200

bit representation = 00000010 00000000 00000010 00000000

Check pending info:

Constraint status = x00

Constraint RID = Page 0 Slot 0

last BID = x00000000

Slot 3:

Offset Location = 2892 (xB4C)

Record Length = 24 (x18)

Record Type = Table Description Record

Number of Columns = 2

Column 1:

Type is Long Integer

Length = 4

Prohibits NULLs

Prohibits Default

Fixed offset: 0

Column 2:

Type is Fixed Length Character String

Length = 10

Allows NULLs

Prohibits Default

Fixed offset: 4

Slot 4:

Offset Location = 2869 (xB35)

Record Length = 23 (x17)

Record Type = Table Data Record (FIXEDVAR)

Fixed part length value = 15

Column 1:

Fixed offset: 0

Type is Long Integer

Value = 1

Column 2:

Fixed offset: 4

Type is Fixed Length Character String

61202020 20202020 2020 a

Slot5:

Offset Location = 2846 (xB1E)

Record Length = 23 (x17)

Record Type = Table Data Record (FIXEDVAR)

Fixed part length value = 15

Column 1:

Fixed offset: 0

Type is Long Integer

Value = 2

Column 2:

Fixed offset: 4

Type is Fixed Length Character String

61202020 20202020 2020 a

Slot 6:

Offset Location = 2823 (xB07)

Record Length = 23 (x17)

Record Type = Table Data Record (FIXEDVAR)

Fixed part length value = 15

Column 1:

Fixed offset: 0

Type is Long Integer

Value = 3

Column 2:

Fixed offset: 4

Type is Fixed Length Character String

61202020 20202020 2020 a

Slot 7:

Offset Location = 2800 (xAF0)

Record Length = 23 (x17)

Record Type = Table Data Record (FIXEDVAR)

Fixed part length value = 15

Column1:

Fixed offset: 0

Type is Long Integer

Value = 4

Column2:

Fixed offset: 4

Type is Fixed Length Character String

61202020 20202020 2020 a

Slots Summary: Total=8, In-use=8, Deleted=0.

Table object report phase end.

______________________________________

DB2DART Processing completed with warning(s)!

Warning(s) detected during processing.

______________________________________

Complete DB2DART report found in:

/home/db2inst1/sqllib/db2dump/DART0000/EOS.RPT

_______ D A R T P R O C E S S I N G C O M P L E T E _______

找到Solt 7 (0x07)，ok，你現(xiàn)在可以清楚的知道應(yīng)用等待的Row為(4,a)

總結(jié)

通過上面的方法，我們簡(jiǎn)單描述了一個(gè)db2鎖問題的定位方法，希望能給大家在分析和定位應(yīng)用性能問題的時(shí)候起到一定的幫助。