MySQL死鎖日志是什么意思呢？在MySQL中，死鎖是指兩個(gè)或多個(gè)事務(wù)在互相等待對(duì)方所持有的鎖資源時(shí)，導(dǎo)致所有事務(wù)無(wú)法繼續(xù)執(zhí)行的情況。

當(dāng)發(fā)生死鎖的情況時(shí)，MySQL會(huì)自動(dòng)記錄死鎖事件時(shí)的相關(guān)信息，包括死鎖發(fā)生的時(shí)間、涉及的事務(wù)ID和鎖信息等。這些信息被稱為死鎖日志。

死鎖日志對(duì)于診斷和解決死鎖問(wèn)題非常有用。通過(guò)分析死鎖日志，可以找到導(dǎo)致死鎖的原因，進(jìn)而對(duì)相關(guān)應(yīng)用程序作出調(diào)整，以避免類(lèi)似的死鎖事件再次發(fā)生。

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LATEST DETECTED DEADLOCK
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2019-09-01 15:06:18 0x7f7280c1a700
*** (1) TRANSACTION:
TRANSACTION 4496826212, ACTIVE 0 sec inserting
mysql tables in use 1, locked 1
LOCK WAIT 4 lock struct(s), heap size 1184, 3 row lock(s), undo log entries 2
MySQL thread id 786597, OS thread handle 139760000173824, query id 132390812 localhost root update
insert into test2 (id,cnt) values (1,1)
*** (1) WAITING FOR THIS LOCK TO BE GRANTED:
RECORD LOCKS space id 126069 page no 3 n bits 72 index `PRIMARY` of table `test`.`test2` trx id 4496826212 lock_mode X locks rec but not gap waiting
Record lock, heap no 3 PHYSICAL RECORD: n_fields 2; compact format; info bits 0
 0: len 8; hex 73757072656d7570; asc supremup;;
 1: len 4; hex 80000001; asc     ;;
*** (2) TRANSACTION:
TRANSACTION 4496826761, ACTIVE 0 sec inserting
mysql tables in use 1, locked 1
4 lock struct(s), heap size 1184, 3 row lock(s), undo log entries 2
MySQL thread id 786570, OS thread handle 139787712196864, query id 132390881 localhost root update
insert into test2 (id,cnt) values(2,2)
*** (2) HOLDS THE LOCK(S):
RECORD LOCKS space id 126069 page no 3 n bits 72 index `PRIMARY` of table `test`.`test2` trx id 4496826761 lock mode S locks rec but not gap
Record lock, heap no 3 PHYSICAL RECORD: n_fields 2; compact format; info bits 0
 0: len 8; hex 73757072656d7570; asc supremup;;
 1: len 4; hex 80000001; asc     ;;
*** (2) WAITING FOR THIS LOCK TO BE GRANTED:
RECORD LOCKS space id 126069 page no 3 n bits 72 index `PRIMARY` of table `test`.`test2` trx id 4496826761 lock_mode X locks rec but not gap waiting
Record lock, heap no 3 PHYSICAL RECORD: n_fields 2; compact format; info bits 0
 0: len 8; hex 73757072656d7570; asc supremup;;
 1: len 4; hex 80000001; asc     ;;
*** WE ROLL BACK TRANSACTIONS (2)

上面是一個(gè)典型的死鎖日志的示例。通過(guò)分析該日志，可以看到有兩個(gè)事務(wù)（TRANSACTION 4496826212和TRANSACTION 4496826761）在同時(shí)插入數(shù)據(jù)，并且都等待對(duì)方釋放鎖資源。由此導(dǎo)致死鎖的發(fā)生。最后MySQL強(qiáng)行終止了其中一個(gè)事務(wù)，來(lái)解決死鎖問(wèn)題。