死锁报告中“锁定记录但不等待间隙”的含义

12

  1. 关于locks rec but not gap waitingTRANSACTION（1）中的含义，哪个正确？

    • 已经授予间隙锁，正在等待聚集索引X锁？
    • 已经授予聚集索引X锁，正在等待间隙锁？

  2. Transaction（1）中有31行。这些行的含义是什么？这代表间隙锁定吗？

     0: len 4; hex 800c20d6; asc     ;;
 ....
 29: SQL NULL;
 30: SQL NULL;

最新检测到的死锁报告

    LATEST DETECTED DEADLOCK
    ------------------------
    2015-09-25 15:27:24 1b8084000


    *** (1) TRANSACTION:
    TRANSACTION 5226928, ACTIVE 0 sec fetching rows
    mysql tables in use 1, locked 1
    LOCK WAIT 31 lock struct(s), heap size 6544, 548 row lock(s)
    MySQL thread id 71, OS thread handle 0x1b45be000, query id 4085356 localhost root Creating sort index
    SELECT  `rpush_notifications`.* FROM `rpush_notifications`  WHERE (processing = 0 AND delivered = 0 AND failed = 0 AND (deliver_after IS NULL OR deliver_after < '2015-09-25 07:27:24'))  ORDER BY created_at ASC LIMIT 100 FOR UPDATE


    *** (1) WAITING FOR THIS LOCK TO BE GRANTED:
    RECORD LOCKS space id 10287 page no 10901 n bits 152 index `PRIMARY` of table `ct_development`.`rpush_notifications` trx id 5226928 lock_mode X locks rec but not gap waiting
    Record lock, heap no 78 PHYSICAL RECORD: n_fields 31; compact format; info bits 0
     0: len 4; hex 800c20d6; asc     ;;
     1: len 6; hex 0000004fc1aa; asc    O  ;;
     2: len 7; hex 4c0000027b07fe; asc L   {  ;;
     3: len 30; hex 52707573683a3a436c69656e743a3a4163746976655265636f72643a3a41; asc Rpush::Client::ActiveRecord::A; (total 47 bytes);
     4: SQL NULL;
     5: len 30; hex 373838653836643365666465626262626639633464363261626433366132; asc 788e86d3efdebbbbf9c4d62abd36a2; (total 64 bytes);
     6: len 7; hex 64656661756c74; asc default;;
     7: len 7; hex 6869206d6f6d21; asc hi mom!;;
     8: len 13; hex 7b22666f6f223a22626172227d; asc {"foo":"bar"};;
     9: len 4; hex 80015180; asc   Q ;;
     10: len 1; hex 80; asc  ;;
     11: SQL NULL;
     12: len 1; hex 81; asc  ;;
     13: len 5; hex 99973276d8; asc   2v ;;
     14: SQL NULL;
     15: len 0; hex ; asc ;;
     16: SQL NULL;
     17: len 5; hex 99973276d6; asc   2v ;;
     18: len 5; hex 99973276d6; asc   2v ;;
     19: len 1; hex 80; asc  ;;
     20: SQL NULL;
     21: len 1; hex 80; asc  ;;
     22: SQL NULL;
     23: len 4; hex 80000002; asc     ;;
     24: len 4; hex 80000000; asc     ;;
     25: SQL NULL;
     26: SQL NULL;
     27: len 1; hex 80; asc  ;;
     28: SQL NULL;
     29: SQL NULL;
     30: SQL NULL;

    *** (2) TRANSACTION:

    TRANSACTION 5226922, ACTIVE 0 sec updating or deleting, thread declared inside InnoDB 0
    mysql tables in use 1, locked 1
    3 lock struct(s), heap size 1184, 2 row lock(s), undo log entries 1
    MySQL thread id 1446, OS thread handle 0x1b8084000, query id 4085345 localhost root updating
    UPDATE `rpush_notifications` SET processing = 0, delivered = 0, delivered_at = NULL, failed = 1, failed_at = '2015-09-25 07:27:24', error_code = NULL, error_description = '' WHERE `rpush_notifications`.`id` IN (794838, 794839)


    *** (2) HOLDS THE LOCK(S):
    RECORD LOCKS space id 10287 page no 10901 n bits 152 index `PRIMARY` of table `ct_development`.`rpush_notifications` trx id 5226922 lock_mode X locks rec but not gap
    Record lock, heap no 78 PHYSICAL RECORD: n_fields 31; compact format; info bits 0
     0: len 4; hex 800c20d6; asc     ;;
     1: len 6; hex 0000004fc1aa; asc    O  ;;
     2: len 7; hex 4c0000027b07fe; asc L   {  ;;
     3: len 30; hex 52707573683a3a436c69656e743a3a4163746976655265636f72643a3a41; asc Rpush::Client::ActiveRecord::A; (total 47 bytes);
     4: SQL NULL;
     5: len 30; hex 373838653836643365666465626262626639633464363261626433366132; asc 788e86d3efdebbbbf9c4d62abd36a2; (total 64 bytes);
     6: len 7; hex 64656661756c74; asc default;;
     7: len 7; hex 6869206d6f6d21; asc hi mom!;;
     8: len 13; hex 7b22666f6f223a22626172227d; asc {"foo":"bar"};;
     9: len 4; hex 80015180; asc   Q ;;
     10: len 1; hex 80; asc  ;;
     11: SQL NULL;
     12: len 1; hex 81; asc  ;;
     13: len 5; hex 99973276d8; asc   2v ;;
     14: SQL NULL;
     15: len 0; hex ; asc ;;
     16: SQL NULL;
     17: len 5; hex 99973276d6; asc   2v ;;
     18: len 5; hex 99973276d6; asc   2v ;;
     19: len 1; hex 80; asc  ;;
     20: SQL NULL;
     21: len 1; hex 80; asc  ;;
     22: SQL NULL;
     23: len 4; hex 80000002; asc     ;;
     24: len 4; hex 80000000; asc     ;;
     25: SQL NULL;
     26: SQL NULL;
     27: len 1; hex 80; asc  ;;
     28: SQL NULL;
     29: SQL NULL;
     30: SQL NULL;

    *** (2) WAITING FOR THIS LOCK TO BE GRANTED:
    RECORD LOCKS space id 10287 page no 7992 n bits 1480 index `index_rpush_notifications_multi` of table `ct_development`.`rpush_notifications` trx id 5226922 lock_mode X locks rec but not gap waiting
    Record lock, heap no 1279 PHYSICAL RECORD: n_fields 3; compact format; info bits 0
     0: len 1; hex 80; asc  ;;
     1: len 1; hex 80; asc  ;;
     2: len 4; hex 800c20d6; asc     ;;

    *** WE ROLL BACK TRANSACTION (2)

表架构

CREATE TABLE `rpush_notifications` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `type` varchar(255) NOT NULL,
  `badge` int(11) DEFAULT NULL,
  `device_token` varchar(64) DEFAULT NULL,
  `sound` varchar(255) DEFAULT 'default',
  `alert` varchar(255) DEFAULT NULL,
  `data` text,
  `expiry` int(11) DEFAULT '86400',
  `delivered` tinyint(1) NOT NULL DEFAULT '0',
  `delivered_at` datetime DEFAULT NULL,
  `failed` tinyint(1) NOT NULL DEFAULT '0',
  `failed_at` datetime DEFAULT NULL,
  `error_code` int(11) DEFAULT NULL,
  `error_description` text,
  `deliver_after` datetime DEFAULT NULL,
  `created_at` datetime DEFAULT NULL,
  `updated_at` datetime DEFAULT NULL,
  `alert_is_json` tinyint(1) DEFAULT '0',
  `collapse_key` varchar(255) DEFAULT NULL,
  `delay_while_idle` tinyint(1) NOT NULL DEFAULT '0',
  `registration_ids` mediumtext,
  `app_id` int(11) NOT NULL,
  `retries` int(11) DEFAULT '0',
  `uri` varchar(255) DEFAULT NULL,
  `fail_after` datetime DEFAULT NULL,
  `processing` tinyint(1) NOT NULL DEFAULT '0',
  `priority` int(11) DEFAULT NULL,
  `url_args` text,
  `category` varchar(255) DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `index_rapns_notifications_multi` (`app_id`,`delivered`,`failed`,`deliver_after`),
  KEY `index_rpush_notifications_multi` (`delivered`,`failed`)
) ENGINE=InnoDB AUTO_INCREMENT=337371 DEFAULT CHARSET=utf8;
mysql  deadlock 
— 吕恩
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Answers:

20

问题1： InnoDB试图在行上获得排他锁（实际上是对聚集索引记录PK的锁），而不是周围的间隙（间隙锁）。您可以在此处阅读有关记录和间隙锁定的更多信息：https : //dev.mysql.com/doc/refman/5.7/en/innodb-locking.html#innodb-record-locks

排他锁定请求来自添加到SELECT语句中的“ for update”子句。请记住，使用默认值的可重复读取隔离级别（选择@@ session.tx_isolation）时，排他锁将放置在检查 SELECT的每一行上，而不仅是返回的行（匹配的行） WHERE子句中的所有谓词）。因此，您可以通过以下方式使用复合索引来减少检查的行数，从而减少所持有的锁，这将大大减少冲突的机会：处理，已交付，失败，deliver_after

我不知道这些列的基数（唯一值的数量）是什么，但是通常应该从最高基数到最低基数在组合索引中列出它们。

 

问题 2：31是它试图/等待获得排它锁的索引记录（或逻辑上为行）中的字段数。InnoDB使用集群PK，因此集群索引（PK）中的记录包含每个用户定义列的字段-在push_notifications表的情况下为29个字段：id ... category-始终有两个附加字段每个InnoDB表的内部字段：6字节的事务ID字段和7字节的滚动指针字段（这些用于MVCC）。因此，您看到的列出的31个项目是我们等待锁定的索引记录（或逻辑上为行）中包含的字段。

 

仅供参考：您可以在5.6+版本中使用新的Information_Schema表获得InnoDB锁的进一步细分：https ://dev.mysql.com/doc/refman/5.7/en/innodb-information-schema-transactions.html

在新的SYS模式中，也有一些不错的报告，该报告包含在MySQL 5.7+中的服务器中（尽管尚未完全进入在线手册中）：https : //github.com/MarkLeith/mysql-sys ＃innodb_lock_waits--xinnodb_lock_waits

如果您感兴趣，可以在MySQL 5.6中手动安装最新的SYS模式：https : //github.com/MarkLeith/mysql-sys/blob/master/sys_56.sql

有关更多信息，请访问：http : //www.slideshare.net/Leithal/performance-schema-and-sys-schema-in-mysql-57

 

我希望这有帮助！

— 马特·洛德
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