檢視MySQL鎖等待的原因
--sys庫的介紹
mysql 5.6也可以有sys庫（基於performance_schema的檢視）。sys庫是一個開源專案，在githup上早就有，是一個DBA的開源工具，後來mysql感覺好，就放在了mysql5.7上。
下載地址：
[tms@m-db3 ~]$ cd mysql-sys-master
[tms@m-db3 ~]$ mysql < sys_56.sql
這樣，就可以在mysql5.6裡面加入sys庫了，不過mysql 5.6只有88張表，而mysql 5.7有101張，這是因為Mysql 5.7的performace_schema庫裡面又多了幾張表。
sys庫是performance_schema的檢視。
--MySQL鎖等待
當Mysql發生鎖等待情況時，可以透過如下語句來線上檢視：
mysql> select * from sys.innodb_lock_waits \G; *************************** 1. row *************************** wait_started: 2018-07-16 16:25:17 //鎖等待開始的時間,16:25開始等待 wait_age: 00:10:08 //發現問題時已經等待了10分鐘了 wait_age_secs: 608 //608秒，也就是等10分鐘了 locked_table: `iws`.`busi_reconciliationgbgsinfo_inputdetails` //被鎖住的表名 locked_index: PRIMARY //被鎖住的索引 locked_type: RECORD //鎖的型別為行鎖 waiting_trx_id: 13666265 //waiting transaction id，正在等待事務的id號 waiting_trx_started: 2018-07-16 16:24:54 //這個事務是從16:24開始等待 waiting_trx_age: 00:10:31 //等了10分鐘了 waiting_trx_rows_locked: 1 //正在等待的這個事務鎖住了1行記錄 waiting_trx_rows_modified: 0 //正在等待的這個事務修改了0行記錄 waiting_pid: 441805 //這個等待事務的執行緒id是多少，透過show processlist 命令可以查到它，結果看到是一個sleep的執行緒，沒有執行具體sql語句，見下 waiting_query: update busi_reconciliationgbgs ... where id = 4510 //等待鎖釋放的語句 waiting_lock_id: 13666265:2924:21:94 //正在等待的鎖id waiting_lock_mode: X //等待鎖的型別是排它鎖 blocking_trx_id: 13666259 //這個事務id阻塞了waiting lock blocking_pid: 441803 阻塞事務的pid blocking_query: NULL //阻塞事務的sql語句 blocking_lock_id: 13666259:2924:21:94 blocking_lock_mode: X blocking_trx_started: 2018-07-16 16:24:51 blocking_trx_age: 00:10:34 blocking_trx_rows_locked: 1 blocking_trx_rows_modified: 1 sql_kill_blocking_query: KILL QUERY 441803 sql_kill_blocking_connection: KILL 441803 1 row in set (0.00 sec) ERROR: No query specified
上面看到輸出了很多的東西，看的我都蒙圈了。後來檢視mysql官方文件，慢慢的才發現，其實只關注上面的waiting_pid、waiting_query和blocking_pid、blocking_query四個引數即可；其中waiting_pid和blocking_pid兩個引數就是透過執行show processlist命令裡面輸出的執行緒id號，如下：
mysql> show full processlist \G; *************************** 8. row *************************** Id: 441803 User: iws Host: 172.16.21.7:46121 db: iws Command: Sleep Time: 655 State: Info: NULL *************************** 9. row *************************** Id: 441805 User: iws Host: 172.16.21.7:46122 db: iws Command: Query Time: 652 State: updating Info: update busi_reconciliationgbgsinfo_inputdetails set bgs_id = 1622 , date = '2018-06-24 00:00:00' , awbnumber = '006-85516771' , incidental = 15.00 , entry_exit = 23.00 , warehousing_fee = 0.00 , loading_unloading = 0.00 , other = 0.00 , total = 38.00 , state = 20 , comparison_resultsid = 30 , confirmation_method = '人工' , confirmationid = 'root' , confirmationtime = '2018-07-16 16:25:17' , confirmation_note = '.' , createtime = '2018-06-24 20:00:07' , createrid = '9862ebdbaf3249a88bcaa8f01bde0471' where id = 4510
透過上面兩個的輸出結果，我們明白了，是441803執行緒鎖住了表，造成執行緒441805的等待。
我們看到發生等待的執行緒441805對應的sql語句是：update busi_reconciliationgbgs ... where id = 4510，但是鎖表的執行緒441803對應的sql語句竟然是Null。這就更讓人迷惑了。
於是我默默的翻開了ysql官方文件，原來裡面已經對這個null專門做了說明。
官方文件說，要想找到這個null值對應的阻塞語句，可以透過下面幾個步驟尋找：
a)、根據鎖表的processlist id 441803，運用如下sql，找到null對應的sql語句，如下：
SELECT SQL_TEXT FROM performance_schema.events_statements_current WHERE THREAD_ID in (SELECT THREAD_ID FROM performance_schema.threads WHERE PROCESSLIST_ID=441803)
b)、如果上面找到的sql語句，你還是不能分析出為什麼他們會鎖表，一直拿著鎖不釋放，那麼你可以檢視 performance_schema.events_statements_history表裡面最近執行過的10條sql（假設上面查到的thread_id=28）:
SELECT EVENT_ID,CURRENT_SCHEMA, SQL_TEXT FROM performance_schema.events_statements_history WHERE THREAD_ID in (SELECT THREAD_ID FROM performance_schema.threads WHERE PROCESSLIST_ID=441803) order by event_id
其他：
上面查詢鎖的sql可以只關注已下幾個列，如下：
SELECT wait_started, wait_age, waiting_pid, waiting_query, blocking_trx_id, blocking_pid, blocking_query, blocking_lock_mode, sql_kill_blocking_query FROM sys.innodb_lock_waits
~~~~~~~~~~~~分割線~~~~~~~~~~~~~~~~~
最近我用python 2.6寫了個自動殺鎖的指令碼，只要發現sys.innodb_lock_waits表裡面有鎖表的內容，就殺死相應的sql執行緒，並輸出殺死sql的內容到當前目錄下：
#!/usr/bin/env python
#-*-coding:utf8-*-
#下載rpm包安裝，下載地址：https://dev.mysql.com/downloads/connector/python/,注意mysql-connector-python版本需要是1.1.17的，2.x的版本執行會有問題
from __future__ import print_function
import mysql.connector as mdb
import os
#全域性變數
username = 'root'
password = ''
hostname = 'localhost'
database = 'sys'
#配置資訊
config = {
'user': username,
'password': password,
'host': hostname,
'database': database
}
#定義函式,檢視鎖表的行數
def Get_sys_lock():
show_locked_num = "select count(*) from sys.innodb_lock_waits"
cursor.execute(show_locked_num)
for i in cursor:
locked_sql_num = i[0]
return locked_sql_num
#定義函式，如果有鎖表，就重定向到locked_sql.txt檔案裡面
def show_locked_sql():
count = 0
count1 = 0
#如果日誌檔案存在就刪除
if os.path.isfile('locked_sql.txt'):
os.remove('locked_sql.txt')
if os.path.isfile('null_sql.txt'):
os.remove('null_sql.txt')
if os.path.isfile('last_10_null_sql.txt'):
os.remove('last_10_null_sql.txt')
#引用函式
locked_sql_num = Get_sys_lock()
print("鎖表的行數是：{0}".format(locked_sql_num))
if locked_sql_num > 0: #如果有鎖表
show_locked_sql = " SELECT \
wait_started, \
wait_age, \
waiting_pid, \
waiting_query, \
blocking_trx_id, \
blocking_pid, \
blocking_query, \
blocking_lock_mode, \
sql_kill_blocking_query \
FROM \
sys.innodb_lock_waits \
"
cursor.execute(show_locked_sql)
for i in cursor:
wait_started = i[0]
wait_age = i[1]
waiting_pid = i[2]
waiting_query = i[3]
blocking_trx_id = i[4]
blocking_pid = i[5]
blocking_query = i[6]
blocking_lock_mode = i[7]
sql_kill_blocking_query = i[8]
if not str(blocking_query).strip(): #如果blocking_query字串為Null
#import pdb;pdb.set_trace()
show_null_sql = "SELECT SQL_TEXT FROM performance_schema.events_statements_current WHERE THREAD_ID in (SELECT THREAD_ID FROM performance_schema.threads WHERE PROCESSLIST_ID=%s)" % blocking_pid
conn = mdb.connect(**config)
cursor1 = conn.cursor()
cursor1.execute(show_null_sql)
#print(cursor1.fetchall())
for j in cursor1:
SQL_TEXT = j[0]
print(SQL_TEXT)
cursor1.close
try:
count1 += 1
f = open('null_sql.txt','a') #a表示追加
f.write (
'##########' + 'The ' + str(count1) + ' rows ' + 'Blocking null query對應的具體sql為##########\n' +
'blocking_pid: ' + str(blocking_pid) + '\n'
'sql_text: ' + str(SQL_TEXT) + '\n\n'
)
except OSError as reason:
print('出錯了:' + str(reason))
finally:
f.close
#再檢視null對應的最後10條sql
show_last_10_null_sql = "SELECT EVENT_ID,CURRENT_SCHEMA, SQL_TEXT FROM performance_schema.events_statements_history WHERE THREAD_ID in (SELECT THREAD_ID FROM performance_schema.threads WHERE PROCESSLIST_ID=%s) order by event_id" % blocking_pid
cursor2 = conn.cursor()
cursor2.execute(show_last_10_null_sql)
cursor2.close
#print(cursor1.fetchall())
count2 = 0
for j in cursor2:
EVENT_ID = j[0]
CURRENT_SCHEMA = j[1]
SQL_TEXT = j[2]
try:
count2 += 1
f = open('last_10_null_sql.txt','a') #a表示追加
f.write (
'##########' + 'The ' + str(count2) + ' rows ' + 'laster blocking null query對應的具體sql為##########\n' +
'blocking_pid: ' + str(blocking_pid) + '\n'
'EVENT_ID: ' + str(EVENT_ID) + '\n'
'CURRENT_SCHEMA: ' + str(CURRENT_SCHEMA) + '\n'
'SQL_TEXT: ' + str(SQL_TEXT) + '\n\n'
)
except OSError as reason:
print('出錯了:' + str(reason))
finally:
f.close
#把鎖表的情況重定向到一個locked_sql.txt檔案裡面
try:
count += 1
f = open('locked_sql.txt','a') #a表示追加
f.write('##########' + 'The ' + str(count) + ' rows' + '###########\n')
f.write (
'wait_started: ' + str(wait_started) + '\n' +
'wait_age: ' + str(wait_age) + '\n' +
'waiting_pid: ' + str(waiting_pid ) + '\n' +
'waiting_query: ' + str(waiting_query) + '\n' +
'blocking_trx_id: ' + str(blocking_trx_id) + '\n' +
'blocking_pid: ' + str(blocking_pid) + '\n' +
'blocking_query: ' + str(blocking_query) + '\n' +
'blocking_lock_mode: ' + str(blocking_lock_mode) + '\n' +
'sql_kill_blocking_query: ' + str(sql_kill_blocking_query) + '\n\n'
)
'''
f.write (
'##########' + 'Blocking null query對應的具體sql為##########\n' +
'blocking_pid:' + str(blocking_pid) +
'sql_text:' + str(SQL_TEXT)
)
'''
except OSError as reason:
print('出錯了:' + str(reason))
finally:
f.close
#定義函式，列出當前所有執行的sql執行緒
def show_processlist():
count = 0
#如果日誌檔案存在就刪除
if os.path.isfile('show_processlist.txt'):
os.remove('show_processlist.txt')
#引用函式
locked_sql_num = Get_sys_lock()
#print("鎖表的行數是：{0}".format(locked_sql_num))
if locked_sql_num > 0: #如果有鎖表
show_processlist = "select \
id, \
user, \
host, \
db, \
time, \
state, \
info \
from information_schema.`PROCESSLIST` order by time desc \
"
cursor.execute(show_processlist)
for i in cursor:
id = i[0]
user = i[1]
host = i[2]
db = i[3]
time = i[4]
state = i[5]
info = i[6]
#把鎖表的情況重定向到一個show_processlist.txt檔案裡面
try:
count += 1
f = open('show_processlist.txt','a') #a表示追加
f.write('##########' + 'The ' + str(count) + ' rows' + '###########\n')
f.write (
'id: ' + str(id) + '\n' +
'user: ' + str(user) + '\n' +
'host: ' + str(host) + '\n' +
'db: ' + str(db) + '\n' +
'time: ' + str(time) + '\n' +
'state: ' + str(state) + '\n' +
'info: ' + str(info) + '\n\n'
)
except OSError as reason:
print('出錯了:' + str(reason))
finally:
f.close
#定義函式，如果有鎖表，就殺死
def kill_locked_sql():
#引用函式
locked_sql_num = Get_sys_lock()
#print("鎖表的行數是：{0}".format(locked_sql_num))
if locked_sql_num > 0: #如果有鎖表
execute_locked_sql = " SELECT \
sql_kill_blocking_query \
FROM \
sys.innodb_lock_waits \
"
cursor.execute(execute_locked_sql)
for i in cursor:
sql_kill_blocking_query = i[0]
conn = mdb.connect(**config)
cursor1 = conn.cursor()
try:
cursor1.execute(sql_kill_blocking_query)
except:
print('出錯了')
cursor1.close
#主程式
conn = mdb.connect(**config)
cursor = conn.cursor()
show_locked_sql()
show_processlist()
kill_locked_sql()
cursor.close
conn.close
--參考文件：
https://dev.mysql.com/doc/refman/8.0/en/sys-innodb-lock-waits.html
https://dev.mysql.com/doc/refman/8.0/en/innodb-information-schema-examples.html#innodb-information-schema-examples-null-blocking-query
來自 “ ITPUB部落格 ” ，連結：http://blog.itpub.net/28916011/viewspace-2158012/，如需轉載，請註明出處，否則將追究法律責任。
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