MySQL DeadLock故障排查全過程記錄

發(fā)布時(shí)間：2020-10-01 00:47:07 來源：腳本之家閱讀：184 作者：攜程DBA 欄目：MySQL數(shù)據(jù)庫

【作者】

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

【環(huán)境】

版本號(hào)：5.6.21

隔離級(jí)別：REPEATABLE READ

【問題描述】

接到監(jiān)控報(bào)警，有一個(gè)線上的應(yīng)用DeadLock報(bào)錯(cuò)，每15分鐘會(huì)準(zhǔn)時(shí)出現(xiàn)，報(bào)錯(cuò)統(tǒng)計(jì)如下圖：

MySQL DeadLock故障排查全過程記錄

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(gè)Block，報(bào)TimeOut的錯(cuò)才對(duì)，怎么會(huì)報(bào)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(gè)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?cè)倏匆幌耬xplain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(duì)同一個(gè)表可以使用多個(gè)索引分別進(jìn)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(yàn)證】

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

時(shí)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(shí)間序列5時(shí)所需資源的X鎖，可以再開啟一個(gè)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?yàn)閕ntersect的原因，還需要idxColumn6的鎖，至此思路已經(jīng)清晰，對(duì)整個(gè)分配鎖的信息簡化一下，如下表格（請(qǐng)求到的鎖用青色表示，需獲取但未獲取到的鎖用紅色表示）：

時(shí)間點(diǎn)	Session1	Session2
1	477 SEK
2		485 SEK
3	485 SEK	死鎖發(fā)生

可以看到485 SEK這兩個(gè)資源形成了一個(gè)環(huán)狀，最終發(fā)生死鎖。

【解決方法】

最佳的方法是添加column5和Column6的聯(lián)合索引。
我們環(huán)境當(dāng)時(shí)的情況發(fā)現(xiàn)Column6的篩選度非常低，就刪除了Column6的索引。
10:55左右刪除索引后，報(bào)錯(cuò)沒有再發(fā)生：

總結(jié)

以上就是這篇文章的全部內(nèi)容了，希望本文的內(nèi)容對(duì)大家的學(xué)習(xí)或者工作具有一定的參考學(xué)習(xí)價(jià)值，如果有疑問大家可以留言交流，謝謝大家對(duì)億速云的支持。

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MySQL DeadLock故障排查全過程記錄

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