深入了解mysql長事務(wù)

更新時間：2020年08月10日 10:58:33 作者：mysql技術(shù)

這篇文章主要介紹了mysql長事務(wù)的相關(guān)資料，幫助大家更好的理解和學(xué)習(xí)mysql，感興趣的朋友可以了解下

前言：

本篇文章主要介紹MySQL長事務(wù)相關(guān)內(nèi)容，比如說我們開啟的一個事務(wù)，一直沒提交或回滾會怎樣呢，出現(xiàn)事務(wù)等待情況應(yīng)該如何處理，本篇文章將給你答案。

注意：本篇文章并不聚焦于談?wù)撌聞?wù)隔離級別以及相關(guān)特性。而是介紹長事務(wù)相關(guān)危害以及監(jiān)控處理方法。本文是基于MySQL5.7.23版本，不可重復(fù)讀(RR)隔離級別所做實驗。(語句為\G可以使查詢結(jié)構(gòu)顯示更易讀，但只可以在mysql命令行使用。)

1.什么是長事務(wù)

首先我們先要知道什么是長事務(wù)，顧名思義就是運行時間比較長，長時間未提交的事務(wù)，也可以稱之為大事務(wù)。這類事務(wù)往往會造成大量的阻塞和鎖超時，容易造成主從延遲，要盡量避免使用長事務(wù)。

下面我將演示下如何開啟事務(wù)及模擬長事務(wù)：

#假設(shè)我們有一張stu_tb表，結(jié)構(gòu)及數(shù)據(jù)如下
mysql> show create table stu_tb\G
*************************** 1. row ***************************
    Table: stu_tb
Create Table: CREATE TABLE `stu_tb` (
 `increment_id` int(11) NOT NULL AUTO_INCREMENT COMMENT '自增主鍵',
 `stu_id` int(11) NOT NULL COMMENT '學(xué)號',
 `stu_name` varchar(20) DEFAULT NULL COMMENT '學(xué)生姓名',
 `create_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT '創(chuàng)建時間',
 `update_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT '修改時間',
 PRIMARY KEY (`increment_id`),
 UNIQUE KEY `uk_stu_id` (`stu_id`) USING BTREE
) ENGINE=InnoDB AUTO_INCREMENT=9 DEFAULT CHARSET=utf8 COMMENT='測試學(xué)生表'
1 row in set (0.01 sec)

mysql> select * from stu_tb;
+--------------+--------+----------+---------------------+---------------------+
| increment_id | stu_id | stu_name | create_time     | update_time     |
+--------------+--------+----------+---------------------+---------------------+
|      1 |  1001 | from1  | 2019-09-15 14:27:34 | 2019-09-15 14:27:34 |
|      2 |  1002 | dfsfd  | 2019-09-15 14:27:34 | 2019-09-15 14:27:34 |
|      3 |  1003 | fdgfg  | 2019-09-15 14:27:34 | 2019-09-15 14:27:34 |
|      4 |  1004 | sdfsdf  | 2019-09-15 14:27:34 | 2019-09-15 14:27:34 |
|      5 |  1005 | dsfsdg  | 2019-09-15 14:27:34 | 2019-09-15 14:27:34 |
|      6 |  1006 | fgd   | 2019-09-15 14:27:34 | 2019-09-15 14:27:34 |
|      7 |  1007 | fgds   | 2019-09-15 14:27:34 | 2019-09-15 14:27:34 |
|      8 |  1008 | dgfsa  | 2019-09-15 14:27:34 | 2019-09-15 14:27:34 |
+--------------+--------+----------+---------------------+---------------------+
8 rows in set (0.00 sec)

#顯式開啟事務(wù)，可用begin或start transaction
mysql> start transaction;
Query OK, 0 rows affected (0.00 sec)

mysql> select * from stu_tb where stu_id = 1006 for update;
+--------------+--------+----------+---------------------+---------------------+
| increment_id | stu_id | stu_name | create_time     | update_time     |
+--------------+--------+----------+---------------------+---------------------+
|      6 |  1006 | fgd   | 2019-09-15 14:27:34 | 2019-09-15 14:27:34 |
+--------------+--------+----------+---------------------+---------------------+
1 row in set (0.01 sec)

 #如果我們不及時提交上個事務(wù)，那么這個事務(wù)就變成了長事務(wù)，當(dāng)其他會話要操作這條數(shù)據(jù)時，就會一直等待。

2.如何找到長事務(wù)

遇到事務(wù)等待問題時，我們首先要做的是找到正在執(zhí)行的事務(wù)。information_schema.INNODB_TRX 表中包含了當(dāng)前innodb內(nèi)部正在運行的事務(wù)信息，這個表中給出了事務(wù)的開始時間，我們可以稍加運算即可得到事務(wù)的運行時間。

mysql> select t.*,to_seconds(now())-to_seconds(t.trx_started) idle_time from INFORMATION_SCHEMA.INNODB_TRX t \G
*************************** 1. row ***************************
          trx_id: 6168
         trx_state: RUNNING
        trx_started: 2019-09-16 11:08:27
   trx_requested_lock_id: NULL
     trx_wait_started: NULL
        trx_weight: 3
    trx_mysql_thread_id: 11
         trx_query: NULL
    trx_operation_state: NULL
     trx_tables_in_use: 0
     trx_tables_locked: 1
     trx_lock_structs: 3
   trx_lock_memory_bytes: 1136
      trx_rows_locked: 2
     trx_rows_modified: 0
  trx_concurrency_tickets: 0
    trx_isolation_level: REPEATABLE READ
     trx_unique_checks: 1
  trx_foreign_key_checks: 1
trx_last_foreign_key_error: NULL
 trx_adaptive_hash_latched: 0
 trx_adaptive_hash_timeout: 0
     trx_is_read_only: 0
trx_autocommit_non_locking: 0
         idle_time: 170

在結(jié)果中idle_time是計算產(chǎn)生的，也是事務(wù)的持續(xù)時間。但事務(wù)的trx_query是NUL，這并不是說事務(wù)什么也沒執(zhí)行，一個事務(wù)可能包含多個SQL，如果SQL執(zhí)行完畢就不再顯示了。當(dāng)前事務(wù)正在執(zhí)行，innodb也不知道這個事務(wù)后續(xù)還有沒有sql,啥時候會commit。因此trx_query不能提供有意義的信息。

如果我們想看到這個事務(wù)執(zhí)行過的SQL，看是否可以殺掉長事務(wù)，怎么辦呢？我們可以聯(lián)合其他系統(tǒng)表查詢得到，具體查詢SQL如下：

mysql> select now(),(UNIX_TIMESTAMP(now()) - UNIX_TIMESTAMP(a.trx_started)) diff_sec,b.id,b.user,b.host,b.db,d.SQL_TEXT from information_schema.innodb_trx a inner join
  -> information_schema.PROCESSLIST b
  -> on a.TRX_MYSQL_THREAD_ID=b.id and b.command = 'Sleep'
  -> inner join performance_schema.threads c ON b.id = c.PROCESSLIST_ID
  -> inner join performance_schema.events_statements_current d ON d.THREAD_ID = c.THREAD_ID;
+---------------------+----------+----+------+-----------+--------+-----------------------------------------------------+
| now()        | diff_sec | id | user | host   | db   | SQL_TEXT                      |
+---------------------+----------+----+------+-----------+--------+-----------------------------------------------------+
| 2019-09-16 14:06:26 |    54 | 17 | root | localhost | testdb | select * from stu_tb where stu_id = 1006 for update |
+---------------------+----------+----+------+-----------+--------+-----------------------------------------------------+

上述結(jié)果中diff_sec和上面idle_time表示意思相同，都是代表此事務(wù)持續(xù)的秒數(shù)。SQL_TEXT表示該事務(wù)剛執(zhí)行的SQL。但是呢，上述語句只能查到事務(wù)最后執(zhí)行的SQL，我們知道，一個事務(wù)里可能包含多個SQL，那我們想查詢這個未提交的事務(wù)執(zhí)行過哪些SQL，是否可以滿足呢，答案是結(jié)合events_statements_history系統(tǒng)表也可以滿足需求。下面語句將會查詢出該事務(wù)執(zhí)行過的所有SQL：

mysql> SELECT
  ->  ps.id 'PROCESS ID',
  ->  ps.USER,
  ->  ps.HOST,
  ->  esh.EVENT_ID,
  ->  trx.trx_started,
  ->  esh.event_name 'EVENT NAME',
  ->  esh.sql_text 'SQL',
  ->  ps.time
  -> FROM
  ->  PERFORMANCE_SCHEMA.events_statements_history esh
  ->  JOIN PERFORMANCE_SCHEMA.threads th ON esh.thread_id = th.thread_id
  ->  JOIN information_schema.PROCESSLIST ps ON ps.id = th.processlist_id
  ->  LEFT JOIN information_schema.innodb_trx trx ON trx.trx_mysql_thread_id = ps.id
  -> WHERE
  ->  trx.trx_id IS NOT NULL
  ->  AND ps.USER != 'SYSTEM_USER'
  -> ORDER BY
  ->  esh.EVENT_ID;
+------------+------+-----------+----------+---------------------+------------------------------+-----------------------------------------------------+------+
| PROCESS ID | USER | HOST   | EVENT_ID | trx_started     | EVENT NAME          | SQL                         | time |
+------------+------+-----------+----------+---------------------+------------------------------+-----------------------------------------------------+------+
|     20 | root | localhost |    1 | 2019-09-16 14:18:44 | statement/sql/select     | select @@version_comment limit 1          |  60 |
|     20 | root | localhost |    2 | 2019-09-16 14:18:44 | statement/sql/begin     | start transaction                  |  60 |
|     20 | root | localhost |    3 | 2019-09-16 14:18:44 | statement/sql/select     | SELECT DATABASE()                  |  60 |
|     20 | root | localhost |    4 | 2019-09-16 14:18:44 | statement/com/Init DB    | NULL                        |  60 |
|     20 | root | localhost |    5 | 2019-09-16 14:18:44 | statement/sql/show_databases | show databases                   |  60 |
|     20 | root | localhost |    6 | 2019-09-16 14:18:44 | statement/sql/show_tables  | show tables                     |  60 |
|     20 | root | localhost |    7 | 2019-09-16 14:18:44 | statement/com/Field List   | NULL                        |  60 |
|     20 | root | localhost |    8 | 2019-09-16 14:18:44 | statement/com/Field List   | NULL                        |  60 |
|     20 | root | localhost |    9 | 2019-09-16 14:18:44 | statement/sql/select     | select * from stu_tb                |  60 |
|     20 | root | localhost |    10 | 2019-09-16 14:18:44 | statement/sql/select     | select * from stu_tb where stu_id = 1006 for update |  60 |
+------------+------+-----------+----------+---------------------+------------------------------+-----------------------------------------------------+------+

從上述結(jié)果中我們可以看到該事務(wù)從一開始到現(xiàn)在執(zhí)行過的所有SQL，當(dāng)我們把該事務(wù)相關(guān)信息都查詢清楚后，我們就可以判定該事務(wù)是否可以殺掉，以免影響其他事務(wù)造成等待現(xiàn)象。

在這里稍微拓展下，長事務(wù)極易造成阻塞或者死鎖現(xiàn)象，通常情況下我們可以首先查詢 sys.innodb_lock_waits 視圖確定有沒有事務(wù)阻塞現(xiàn)象：

#假設(shè)一個事務(wù)執(zhí)行 select * from stu_tb where stu_id = 1006 for update
#另外一個事務(wù)執(zhí)行 update stu_tb set stu_name = 'wang' where stu_id = 1006

mysql> select * from sys.innodb_lock_waits\G
*************************** 1. row ***************************
        wait_started: 2019-09-16 14:34:32
          wait_age: 00:00:03
        wait_age_secs: 3
        locked_table: `testdb`.`stu_tb`
        locked_index: uk_stu_id
         locked_type: RECORD
       waiting_trx_id: 6178
     waiting_trx_started: 2019-09-16 14:34:32
       waiting_trx_age: 00:00:03
   waiting_trx_rows_locked: 1
  waiting_trx_rows_modified: 0
         waiting_pid: 19
        waiting_query: update stu_tb set stu_name = 'wang' where stu_id = 1006
       waiting_lock_id: 6178:47:4:7
      waiting_lock_mode: X
       blocking_trx_id: 6177
        blocking_pid: 20
       blocking_query: NULL
      blocking_lock_id: 6177:47:4:7
     blocking_lock_mode: X
    blocking_trx_started: 2019-09-16 14:18:44
      blocking_trx_age: 00:15:51
  blocking_trx_rows_locked: 2
 blocking_trx_rows_modified: 0
   sql_kill_blocking_query: KILL QUERY 20
sql_kill_blocking_connection: KILL 20

上述結(jié)果顯示出被阻塞的SQL以及鎖的類型，更強大的是殺掉會話的語句也給出來了。但是并沒有找到阻塞會話執(zhí)行的SQL，如果我們想找出更詳細(xì)的信息，可以使用下面語句：

mysql> SELECT
  ->  tmp.*,
  ->  c.SQL_Text blocking_sql_text,
  ->  p.HOST blocking_host
  -> FROM
  ->  (
  ->  SELECT
  ->   r.trx_state wating_trx_state,
  ->   r.trx_id waiting_trx_id,
  ->   r.trx_mysql_thread_Id waiting_thread,
  ->   r.trx_query waiting_query,
  ->   b.trx_state blocking_trx_state,
  ->   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
  ->  ) tmp,
  ->  information_schema.PROCESSLIST p,
  ->  PERFORMANCE_SCHEMA.events_statements_current c,
  ->  PERFORMANCE_SCHEMA.threads t
  -> WHERE
  ->  tmp.blocking_thread = p.id
  ->  AND t.thread_id = c.THREAD_ID
  ->  AND t.PROCESSLIST_ID = p.id \G
*************************** 1. row ***************************
 wating_trx_state: LOCK WAIT
  waiting_trx_id: 6180
  waiting_thread: 19
   waiting_query: update stu_tb set stu_name = 'wang' where stu_id = 1006
blocking_trx_state: RUNNING
  blocking_trx_id: 6177
  blocking_thread: 20
  blocking_query: NULL
 blocking_sql_text: select * from stu_tb where stu_id = 1006 for update
   blocking_host: localhost

上面結(jié)果顯得更加清晰，我們可以清楚的看到阻塞端及被阻塞端事務(wù)執(zhí)行的語句，有助于我們排查并確認(rèn)是否可以殺掉阻塞的會話。

3.監(jiān)控長事務(wù)

現(xiàn)實工作中我們需要監(jiān)控下長事務(wù)，定義一個閾值，比如說30s 執(zhí)行時間超過30s的事務(wù)即為長事務(wù)，要求記錄并告警出來，提醒管理人員去處理。下面給出監(jiān)控腳本，各位可以參考下，根據(jù)需求改動使用：

#!/bin/bash
# -------------------------------------------------------------------------------
# FileName:  long_trx.sh
# Describe:  monitor long transaction
# Revision:  1.0
# Date:    2019/09/16
# Author:   wang

/usr/local/mysql/bin/mysql -N -uroot -pxxxxxx -e "select now(),(UNIX_TIMESTAMP(now()) - UNIX_TIMESTAMP(a.trx_started)) diff_sec,b.id,b.user,b.host,b.db,d.SQL_TEXT from information_schema.innodb_trx a inner join
information_schema.PROCESSLIST b
on a.TRX_MYSQL_THREAD_ID=b.id and b.command = 'Sleep'
inner join performance_schema.threads c ON b.id = c.PROCESSLIST_ID
inner join performance_schema.events_statements_current d ON d.THREAD_ID = c.THREAD_ID;" | while read A B C D E F G H
do
 if [ "$C" -gt 30 ]
   then
   echo $(date +"%Y-%m-%d %H:%M:%S")
   echo "processid[$D] $E@$F in db[$G] hold transaction time $C SQL:$H"
 fi
done >> /tmp/longtransaction.txt

簡單說明一下，這里的-gt 30是30秒鐘的意思，只要超過了30秒鐘就認(rèn)定是長事務(wù)，可以根據(jù)實際需要自定義。將該腳本加入定時任務(wù)中即可執(zhí)行。

總結(jié)：

本文主要介紹了長事務(wù)相關(guān)內(nèi)容，怎樣找到長事務(wù)，怎么處理長事務(wù)，如何監(jiān)控長事務(wù)?？赡苡行┬』锇閷κ聞?wù)理解還不多，希望這篇文章對你有所幫助。由于本篇文章列出的查詢事務(wù)相關(guān)語句較多，現(xiàn)總結(jié)如下：

# 查詢所有正在運行的事務(wù)及運行時間
select t.*,to_seconds(now())-to_seconds(t.trx_started) idle_time from INFORMATION_SCHEMA.INNODB_TRX t \G

# 查詢事務(wù)詳細(xì)信息及執(zhí)行的SQL
select now(),(UNIX_TIMESTAMP(now()) - UNIX_TIMESTAMP(a.trx_started)) diff_sec,b.id,b.user,b.host,b.db,d.SQL_TEXT from information_schema.innodb_trx a inner join information_schema.PROCESSLIST b
on a.TRX_MYSQL_THREAD_ID=b.id and b.command = 'Sleep'
inner join performance_schema.threads c ON b.id = c.PROCESSLIST_ID
inner join performance_schema.events_statements_current d ON d.THREAD_ID = c.THREAD_ID;

# 查詢事務(wù)執(zhí)行過的所有歷史SQL記錄
SELECT
 ps.id 'PROCESS ID',
 ps.USER,
 ps.HOST,
 esh.EVENT_ID,
 trx.trx_started,
 esh.event_name 'EVENT NAME',
 esh.sql_text 'SQL',
 ps.time 
FROM
 PERFORMANCE_SCHEMA.events_statements_history esh
 JOIN PERFORMANCE_SCHEMA.threads th ON esh.thread_id = th.thread_id
 JOIN information_schema.PROCESSLIST ps ON ps.id = th.processlist_id
 LEFT JOIN information_schema.innodb_trx trx ON trx.trx_mysql_thread_id = ps.id 
WHERE
 trx.trx_id IS NOT NULL 
 AND ps.USER != 'SYSTEM_USER' 
ORDER BY
 esh.EVENT_ID;
 
 # 簡單查詢事務(wù)鎖
 select * from sys.innodb_lock_waits\G
 
 # 查詢事務(wù)鎖詳細(xì)信息
 SELECT
 tmp.*,
 c.SQL_Text blocking_sql_text,
 p.HOST blocking_host
FROM
 (
 SELECT
  r.trx_state wating_trx_state,
  r.trx_id waiting_trx_id,
  r.trx_mysql_thread_Id waiting_thread,
  r.trx_query waiting_query,
  b.trx_state blocking_trx_state,
  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 
 ) tmp,
 information_schema.PROCESSLIST p,
 PERFORMANCE_SCHEMA.events_statements_current c,
 PERFORMANCE_SCHEMA.threads t
WHERE
 tmp.blocking_thread = p.id 
 AND t.thread_id = c.THREAD_ID 
 AND t.PROCESSLIST_ID = p.id \G

以上就是深入了解mysql長事務(wù)的詳細(xì)內(nèi)容，更多關(guān)于mysql長事務(wù)的資料請關(guān)注腳本之家其它相關(guān)文章！

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