MySQL DeadLock故障排查全過程記錄

更新時間：2019年01月03日 10:51:21 作者：攜程DBA

這篇文章主要給大家介紹了關(guān)于MySQL DeadLock故障排查的全過程，文中通過示例代碼介紹的非常詳細，對大家的學習或者工作具有一定的參考學習價值，需要的朋友們下面隨著小編來一起學習學習吧

【作者】

劉博：攜程技術(shù)保障中心數(shù)據(jù)庫高級經(jīng)理，主要關(guān)注Sql server和Mysql的運維和故障處理。

【環(huán)境】

版本號：5.6.21

隔離級別：REPEATABLE READ

【問題描述】

接到監(jiān)控報警，有一個線上的應(yīng)用DeadLock報錯，每15分鐘會準時出現(xiàn)，報錯統(tǒng)計如下圖：

登錄Mysql服務(wù)器查看日志：

mysql> show engine innodb status\G

*** (1) TRANSACTION:

TRANSACTION 102973, ACTIVE 11 sec starting index read

mysql tables in use 3, locked 3

LOCK WAIT 4 lock struct(s), heap size 1136, 3 row lock(s)

MySQL thread id 6, OS thread handle 140024996574976, query id 83 localhost us updating

UPDATE TestTable

SET column1 = 1,

Column2 = sysdate(),

Column3= '026'

Column4 = 0

AND column5 = 485

AND column6 = 'SEK'

*** (1) WAITING FOR THIS LOCK TO BE GRANTED:

RECORD LOCKS space id 417 page no 1493 n bits 1000 index idx_column6 of table test.TestTable trx id 102973 lock_mode X waiting

Record lock, heap no 859 PHYSICAL RECORD: n_fields 2; compact format; info bits 0

0: len 3; hex 53454b; asc SEK;;

1: len 8; hex 80000000007e1452; asc ~ R;;

*** (2) TRANSACTION:

TRANSACTION 102972, ACTIVE 26 sec starting index read

mysql tables in use 3, locked 3

219 lock struct(s), heap size 24784, 2906 row lock(s), undo log entries 7

MySQL thread id 5, OS thread handle 140024996841216, query id 84 localhost us updating

UPDATE TestTable

SET Column1 = 1,

Column2 = sysdate(),

Column3 = '026'

Column4 = 0

AND Column5 = 485

AND Column6 = 'SEK'

*** (2) HOLDS THE LOCK(S):

RECORD LOCKS space id 417 page no 1493 n bits 1000 index idx_Column6 of table test.TestTable trx id 102972 lock_mode X

Record lock, heap no 1 PHYSICAL RECORD: n_fields 1; compact format; info bits 0

0: len 8; hex 73757072656d756d; asc supremum;;


Record lock, heap no 859 PHYSICAL RECORD: n_fields 2; compact format; info bits 0

0: len 3; hex 53454b; asc SEK;;

1: len 8; hex 80000000007e1452; asc ~ R;;

*** (2) WAITING FOR THIS LOCK TO BE GRANTED:

RECORD LOCKS space id 601 page no 89642 n bits 1000 index idx_column6 of table test.TestTable trx id 32231892482 lock_mode X locks rec but not gap waiting

Record lock, heap no 38 PHYSICAL RECORD: n_fields 2; compact format; info bits 0

0: len 3; hex 53454b; asc SEK;;

1: len 8; hex 80000000007eea14; asc ~ ;;

大致一看，更新同一索引的同一行，應(yīng)該是一個Block，報TimeOut的錯才對，怎么會報DeadLock?

【初步分析】

先分析下(2) TRANSACTION，TRANSACTION 32231892482。

等待的鎖信息為：

0: len 3; hex 53454b; asc SEK;;

1: len 8; hex 80000000007eea14; asc

持有的鎖信息為：

0: len 3; hex 53454b; asc SEK;;

1: len 8; hex 80000000007eeac4; asc

再先分析下(1) TRANSACTION，TRANSACTION 32231892617。

等待的鎖信息為：

0: len 3; hex 53454b; asc SEK;;

1: len 8; hex 80000000007eeac4; asc

于是可以畫出的死鎖表，兩個資源相互依賴，造成死鎖：

TRANSACTION	Hold	Wait
32231892617	53454b\80000000007eea14	53454b\80000000007eeac4
32231892482	53454b\80000000007eeac4	53454b\80000000007eea14

讓我們再看一下explain結(jié)果：

mysql>desc UPDATE TestTable SET Column1=1, Column2 = sysdate(),Column3 = '025' Column4 = 0 AND Column5 = 477 AND Column6 = 'SEK' \G;

*************************** 1. row ***************************

id: 1

select_type: UPDATE

table: TestTable

partitions: NULL

type: index_merge

possible_keys: column5_index,idx_column5_column6_Column1,idxColumn6

key: column5_index,idxColumn6

key_len: 8,9

ref: NULL

rows: 7

filtered: 100.00

Extra: Using intersect(column5_index,idxColumn6); Using where

可以看到 EXTRA 列：

Using intersect(column5_index,idxColumn6)

從5.1開始，引入了 index merge 優(yōu)化技術(shù)，對同一個表可以使用多個索引分別進行條件掃描。

相關(guān)文檔：http://dev.mysql.com/doc/refman/5.7/en/index-merge-optimization.html

The Index Merge method is used to retrieve rows with several range scans and to merge their results into one. The merge can produce unions, intersections, or unions-of-intersections of its underlying scans. This access method merges index scans from a single table; it does not merge scans across multiple tables.

【模擬與驗證】

根據(jù)以上初步分析，猜測應(yīng)該就是intersect造成的，于是在測試環(huán)境模擬驗證，開啟2個session模擬死鎖：

時間序列	Session1	Session2
1	Begin；
2	UPDATE TestTable SET Column2 = sysdate() Column4 = 0 AND Column5 = 47 AND Column6 = 'SEK 執(zhí)行成功，影響7行
3		Begin；
4		UPDATE TestTable SET Column2 = sysdate(),Column4 = 0 AND Column5 = 485 AND Column6 = 'SEK'；被Blocking
5	UPDATE TestTable SET Column2 = sysdate(),Column4 = 0 AND Column5 = 485 AND Column6 = 'SEK'；執(zhí)行成功	ERROR 1213 (40001): Deadlock found when trying to get lock; try restarting transaction

依據(jù)以上信息可以發(fā)現(xiàn)Session2雖然被Block了，但也獲取了一些Session1在時間序列5時所需資源的X鎖，可以再開啟一個查詢select count(Column5) from TestTable where Column5 = 485，設(shè)置SET TRANSACTION ISOLATION LEVEL SERIALIZABLE，去查詢Column5 = 485的行，觀察鎖等待的信息：
mysql> SELECT r.trx_id waiting_trx_id, r.trx_mysql_thread_id waiting_thread, r.trx_query waiting_query, b.trx_id

mysql> SELECT r.trx_id waiting_trx_id, r.trx_mysql_thread_id waiting_thread, r.trx_query waiting_query, b.trx_id blocking_trx_id, b.trx_mysql_thread_id blocking_thread, b.trx_query blocking_query FROM information_schema.innodb_lock_waits w INNER JOIN information_schema.innodb_trx b ON b.trx_id = w.blocking_trx_id INNER JOIN information_schema.innodb_trx r ON r.trx_id = w.requesting_trx_id \G;

*************************** 1. row ***************************

waiting_trx_id: 103006

waiting_thread: 36

waiting_query: UPDATE TestTable SET Column1 = 1, Column2 = sysdate(), Column3 = '026' Column4 = 0 AND Column5 = 485 AND Column6 = 'SEK'

blocking_trx_id: 103003

blocking_thread: 37

blocking_query: NULL

*************************** 2. row ***************************

waiting_trx_id: 421500433538672

waiting_thread: 39

waiting_query: select count(Column5) from TestTable where Column5 = 485

blocking_trx_id: 103006

blocking_thread: 36

blocking_query: UPDATE TestTable SET Column1 = 1, Column2 = sysdate(), Column3 = '026' Column4 = 0 AND Column5 = 485 AND Column6 = 'SEK'

2 rows in set, 1 warning (0.00 sec)

mysql> select * from information_schema.innodb_lock_waits \G;

*************************** 1. row ***************************

requesting_trx_id: 103006

requested_lock_id: 103006:417:1493:859

blocking_trx_id: 103003

blocking_lock_id: 103003:417:1493:859

*************************** 2. row ***************************

requesting_trx_id: 421500433538672

requested_lock_id: 421500433538672:417:749:2

blocking_trx_id: 103006

blocking_lock_id: 103006:417:749:2

2 rows in set, 1 warning (0.00 sec)

mysql> select * from INNODB_LOCKS \G;

*************************** 1. row ***************************

lock_id: 103006:417:1493:859

lock_trx_id: 103006

lock_mode: X

lock_type: RECORD

lock_table: test.TestTable

lock_index: idxColumn6

lock_space: 417

lock_page: 1493

lock_rec: 859

lock_data: 'SEK', 8262738

*************************** 2. row ***************************

lock_id: 103003:417:1493:859

lock_trx_id: 103003

lock_mode: X

lock_type: RECORD

lock_table:test.TestTable

lock_index: idxColumn6

lock_space: 417

lock_page: 1493

lock_rec: 859

lock_data: 'SEK', 8262738

*************************** 3. row ***************************

lock_id: 421500433538672:417:749:2

lock_trx_id: 421500433538672

lock_mode: S

lock_type: RECORD

lock_table: test.TestTable

lock_index: column5_index

lock_space: 417

lock_page: 749

lock_rec: 2

lock_data: 485, 8317620

*************************** 4. row ***************************

lock_id: 103006:417:749:2

lock_trx_id: 103006

lock_mode: X

lock_type: RECORD

lock_table: test.TestTable

lock_index: column5_index

lock_space: 417

lock_page: 749

lock_rec: 2

lock_data: 485, 8317620

4 rows in set, 1 warning (0.00 sec)

可以看到Session2，trx_id 103006阻塞了trx_id 421500433538672，而trx_id 421500433538672 requested_lock也正好是lock_data: 485, 8317620。由此可見Session2雖然別block了，但是還是獲取到了Index column5_index相關(guān)的鎖。被Block是因為intersect的原因，還需要idxColumn6的鎖，至此思路已經(jīng)清晰，對整個分配鎖的信息簡化一下，如下表格（請求到的鎖用青色表示，需獲取但未獲取到的鎖用紅色表示）：