問(wèn)題描述

問(wèn)題解答

------- TRX HAS BEEN WAITING 28 SEC FOR THIS LOCK TO BE GRANTED:RECORD LOCKS space id 6 page no 4 n bits 80 index idx_a of table `test`.`t` trx id 637972 lock_mode X locks gap before rec insert intention waitingRecord lock, heap no 4 PHYSICAL RECORD: n_fields 2; compact format; info bits 32 0: len 4; hex 8000000b; asc ;; 1: len 6; hex 000000000414; asc ;;

這里說(shuō)的很清楚啊 lock_mode X意味著是排它鎖 gap代表是區(qū)間鎖也就是說(shuō)在insert之前該表加入了區(qū)間排他鎖，為什么呢？因?yàn)橹皥?zhí)行的這句delete from t where a = 11;會(huì)在(negative infinity,11]這個(gè)區(qū)間加上排他鎖，為什么是排他鎖而不是Record Lock呢，因?yàn)槟氵@里的a并非唯一索引,只是一個(gè)普通的索引，具體的看http://dev.mysql.com/doc/refman/5.7/en/innodb-locking.html

mysql默認(rèn)的會(huì)話隔離級(jí)別是repeated read,會(huì)產(chǎn)生更多的gap鎖，如果可以接受幻讀，可以考慮降為read commit級(jí)別，減少鎖沖突的概率。