Kill掉MySQLd_Safe進(jìn)程會(huì)影響MySQLd進(jìn)程？

作者：醒嘞 2023-08-14 08:31:38

mysqld_safe 命令啟動(dòng)，kill 父進(jìn)程(非會(huì)話首進(jìn)程)，不會(huì)導(dǎo)致子進(jìn)程退出；重新啟動(dòng)父進(jìn)程，報(bào)錯(cuò)子進(jìn)程已存在。可以使用mysqld_safe命令啟動(dòng) 改造mysqld_safe腳本，實(shí)現(xiàn)【啟、停mysqld_safe進(jìn)程，不會(huì)影響mysqld進(jìn)程】。

1、背景

公司內(nèi)部看到一則問(wèn)題

ill -9 mysqld_safe 進(jìn)程
systemd 檢測(cè)到 mysqld_safe 進(jìn)程不存在后，重新拉起 mysqld_safe 進(jìn)程
mysqld_safe 進(jìn)程啟動(dòng)后，發(fā)現(xiàn) mysqld 進(jìn)程也被重啟

期望：?jiǎn)ⅰ⑼?mysqld_safe 進(jìn)程，不會(huì)影響 mysqld 進(jìn)程

2、systemd 服務(wù)啟動(dòng)

2.1、復(fù)現(xiàn)問(wèn)題

1)、查看數(shù)據(jù)庫(kù)服務(wù)狀態(tài)

[greatsql@greatsql-1 ~]$ sudo systemctl status db-4306
● db-4306.service - db-4306 Server
   Loaded: loaded (/usr/lib/systemd/system/db-4306.service; disabled; vendor preset: disabled)
   Active: active (running) since Wed 2023-07-19 11:15:18 CST; 6h ago
 Main PID: 14917 (mysqld_safe)
   CGroup: /system.slice/db-4306.service
           ├─14917 /bin/sh /greatsql/svr/greatsql/bin/mysqld_safe --defaults-file=/greatsql/conf/greatsql4306.cnf
           └─16340 /greatsql/svr/greatsql/bin/mysqld --defaults-file=/greatsql/conf/greatsql4306.cnf --basedir=/greatsql/svr/greatsql --datadir=/greatsql/dbdata/data4306/data -...
Jul 19 11:15:18 greatsql-1 systemd[1]: Started db-4306 Server.
Jul 19 11:15:19 greatsql-1 mysqld_safe[14917]: mysqld_safe Adding '/greatsql/svr/GreatSQL-8.0.32-24-Linux-glibc2.17-x86_64/lib/mysql/libjemalloc.so.1' t...or mysqldJul 19 11:15:19 greatsql-1 mysqld_safe[14917]: 2023-07-19T03:15:19.907338Z mysqld_safe Logging to '/greatsql/logs/error4306.log'.
Jul 19 11:15:19 greatsql-1 mysqld_safe[14917]: 2023-07-19T03:15:19.953728Z mysqld_safe Starting mysqld daemon with databases from /greatsql/dbdata/data4306/data
Hint: Some lines were ellipsized, use -l to show in full.

2)、kill -9 mysqld_safe 進(jìn)程，并再次查看數(shù)據(jù)庫(kù)服務(wù)狀態(tài)

[greatsql@greatsql-1 ~]$ kill -9 14917
[greatsql@greatsql-1 ~]$ sudo systemctl status db-4306
● db-4306.service - db-4306 Server
   Loaded: loaded (/usr/lib/systemd/system/db-4306.service; disabled; vendor preset: disabled)
   Active: active (running) since Wed 2023-07-19 18:00:33 CST; 43s ago
 Main PID: 15195 (mysqld_safe)
    Tasks: 50
   CGroup: /system.slice/db-4306.service
           ├─15195 /bin/sh /greatsql/svr/greatsql/bin/mysqld_safe --defaults-file=/greatsql/conf/greatsql4306.cnf
           └─16613 /greatsql/svr/greatsql/bin/mysqld --defaults-file=/greatsql/conf/greatsql4306.cnf --basedir=/greatsql/svr/greatsql --datadir=/greatsql/dbdata/data4306/data -...
Jul 19 18:00:33 greatsql-1 systemd[1]: Started db-4306 Server.
Jul 19 18:00:34 greatsql-1 mysqld_safe[15195]: mysqld_safe Adding '/greatsql/svr/GreatSQL-8.0.32-24-Linux-glibc2.17-x86_64/lib/mysql/libjemalloc.so.1' t...or mysqldJul 19 18:00:34 greatsql-1 mysqld_safe[15195]: 2023-07-19T10:00:34.640240Z mysqld_safe Logging to '/greatsql/logs/error4306.log'.
Jul 19 18:00:34 greatsql-1 mysqld_safe[15195]: 2023-07-19T10:00:34.679333Z mysqld_safe Starting mysqld daemon with databases from /greatsql/dbdata/data4306/data
Hint: Some lines were ellipsized, use -l to show in full.

確實(shí)在 kill -9 mysqld_safe 后，重新拉起了 mysqld_safe 和 mysqld 進(jìn)程(它們的 PID 和之前不一樣)

3)、查看數(shù)據(jù)庫(kù)錯(cuò)誤日志

2023-07-19T18:00:31.933020+08:00 0 [System] [MY-013172] [Server] Received SHUTDOWN from user <via user signal>. Shutting down mysqld (Version: 8.0.32-24).

4)、查看 service 文件

[greatsql@greatsql-1 ~]$ cat /usr/lib/systemd/system/db-4306.service
[Unit]
Description=db-4306 Server
After=network.target

[Install]
WantedBy=multi-user.target

[Service]
User=greatsql
Group=greatsql

Type=simple
ExecStart=/greatsql/svr/greatsql/bin/mysqld_safe --defaults-file=/greatsql/conf/greatsql4306.cnf
Restart=on-failure
LimitNOFILE=1024000
LimitNPROC=1024000
TimeoutStopSec=15
PrivateTmp=false

2.2、分析原因

1)、查看進(jìn)程信息

[greatsql@greatsql-1 ~]$ ps axj |head -1;ps axj |grep 4306 |grep -v grep
 PPID   PID  PGID   SID TTY      TPGID STAT   UID   TIME COMMAND
    1 15195 15195 15195 ?           -1 Ss     986   0:00 /bin/sh /greatsql/svr/greatsql/bin/mysqld_safe --defaults-file=/greatsql/conf/greatsql4306.cnf
15195 16613 15195 15195 ?           -1 Sl     986   0:06 /greatsql/svr/greatsql/bin/mysqld --defaults-file=/greatsql/conf/greatsql4306.cnf --basedir=/greatsql/svr/greatsql --datadir=/greatsql/dbdata/data4306/data --plugin-dir=/greatsql/svr/greatsql/lib/plugin --log-error=/greatsql/logs/error4306.log --open-files-limit=65535 --pid-file=/greatsql/dbdata/data4306/data/mysql.pid --socket=/greatsql/dbdata/data4306/data/mysql.sock --port=4306

mysqld_safe：PID(進(jìn)程 ID)=PGID(進(jìn)程組 ID)=SID(會(huì)話 ID)，說(shuō)明它是會(huì)話首進(jìn)程，也是該進(jìn)程組的組長(zhǎng)

mysqld_safe 的 PID(進(jìn)程 ID)=mysqld 的 PPID(父進(jìn)程 ID)，說(shuō)明 mysqld_safe 是 mysqld 的父進(jìn)程

kill -9 mysqld_safe (會(huì)話首進(jìn)程)，會(huì)向該進(jìn)程組的每一個(gè)進(jìn)程發(fā)送 SIGKILL，導(dǎo)致組中的進(jìn)程被中止

2)、整體流程

mysqld_safe 是會(huì)話首進(jìn)程，kill -9 mysqld_safe，導(dǎo)致組中所有進(jìn)程被 kill
systemd 檢測(cè)到 mysqld_safe 異常退出，Restart=on-failure 觸發(fā)重新拉起 mysqld_safe
mysqld_safe 拉起子進(jìn)程 mysqld

3、mysqld_safe 命令啟動(dòng)

1)、使用 mysqld_safe 啟動(dòng)數(shù)據(jù)庫(kù)

[greatsql@greatsql-1 ~]$ /greatsql/svr/greatsql/bin/mysqld_safe --defaults-file=/greatsql/conf/greatsql4306.cnf &
[1] 18229
[greatsql@greatsql-1 ~]$  mysqld_safe Adding '/greatsql/svr/GreatSQL-8.0.32-24-Linux-glibc2.17-x86_64/lib/mysql/libjemalloc.so.1' to LD_PRELOAD for mysqld
2023-07-19T14:20:19.135297Z mysqld_safe Logging to '/greatsql/logs/error4306.log'.
2023-07-19T14:20:19.173594Z mysqld_safe Starting mysqld daemon with databases from /greatsql/dbdata/data4306/data

2)、查看進(jìn)程信息

[greatsql@greatsql-1 ~]$ ps axj |head -1;ps axj |grep 4306 |grep -v grep
 PPID   PID  PGID   SID TTY      TPGID STAT   UID   TIME COMMAND
17360 18229 18229 17206 pts/7    17360 S      986   0:00 /bin/sh /greatsql/svr/greatsql/bin/mysqld_safe --defaults-file=/greatsql/conf/greatsql4306.cnf
18229 19658 18229 17206 pts/7    17360 Sl     986   0:02 /greatsql/svr/greatsql/bin/mysqld --defaults-file=/greatsql/conf/greatsql4306.cnf --basedir=/greatsql/svr/greatsql --datadir=/greatsql/dbdata/data4306/data --plugin-dir=/greatsql/svr/greatsql/lib/plugin --log-error=/greatsql/logs/error4306.log --open-files-limit=65535 --pid-file=/greatsql/dbdata/data4306/data/mysql.pid --socket=/greatsql/dbdata/data4306/data/mysql.sock --port=4306

PID≠SID，不是會(huì)話首進(jìn)程PGID≠TPGID，是后臺(tái)進(jìn)程組mysqld_safe 的 PID=mysqld 的 PPID，說(shuō)明 mysqld_safe 是 mysqld 的父進(jìn)程

3)、kill -9 mysqld_safe 進(jìn)程，并再次查看進(jìn)程信息

[greatsql@greatsql-1 ~]$ kill -9 18229
[greatsql@greatsql-1 ~]$ ps axj |head -1;ps axj |grep 4306 |grep -v grep
 PPID   PID  PGID   SID TTY      TPGID STAT   UID   TIME COMMAND
    1 19658 18229 17206 pts/7    17360 Sl     986   0:07 /greatsql/svr/greatsql/bin/mysqld --defaults-file=/greatsql/conf/greatsql4306.cnf --basedir=/greatsql/svr/greatsql --datadir=/greatsql/dbdata/data4306/data --plugin-dir=/greatsql/svr/greatsql/lib/plugin --log-error=/greatsql/logs/error4306.log --open-files-limit=65535 --pid-file=/greatsql/dbdata/data4306/data/mysql.pid --socket=/greatsql/dbdata/data4306/data/mysql.sock --port=4306

kill -9 mysqld_safe (非會(huì)話首進(jìn)程)，不影響同組的進(jìn)程(mysqld)，此時(shí) init 進(jìn)程會(huì)自動(dòng)領(lǐng)養(yǎng) mysqld 進(jìn)程

4)、重新啟動(dòng) mysqld_safe 進(jìn)程，并再次查看進(jìn)程信息

[greatsql@greatsql-1 ~]$ /greatsql/svr/greatsql/bin/mysqld_safe --defaults-file=/greatsql/conf/greatsql4306.cnf &
[1] 31401
[greatsql@greatsql-1 ~]$  mysqld_safe Adding '/greatsql/svr/GreatSQL-8.0.32-24-Linux-glibc2.17-x86_64/lib/mysql/libjemalloc.so.1' to LD_PRELOAD for mysqld
2023-07-19T14:38:42.429733Z mysqld_safe Logging to '/greatsql/logs/error4306.log'.
2023-07-19T14:38:42.493870Z mysqld_safe A mysqld process already exists

[1]+  Exit 1                  /greatsql/svr/greatsql/bin/mysqld_safe --defaults-file=/greatsql/conf/greatsql4306.cnf
 
[greatsql@greatsql-1 ~]$ ps axj |head -1;ps axj |grep 4306 |grep -v grep
 PPID   PID  PGID   SID TTY      TPGID STAT   UID   TIME COMMAND
    1 19658 18229 17206 pts/7    17360 Sl     986   0:09 /greatsql/svr/greatsql/bin/mysqld --defaults-file=/greatsql/conf/greatsql4306.cnf --basedir=/greatsql/svr/greatsql --datadir=/greatsql/dbdata/data4306/data --plugin-dir=/greatsql/svr/greatsql/lib/plugin --log-error=/greatsql/logs/error4306.log --open-files-limit=65535 --pid-file=/greatsql/dbdata/data4306/data/mysql.pid --socket=/greatsql/dbdata/data4306/data/mysql.sock --port=4306

mysqld_safe 退出，原因是已存在 mysqld 進(jìn)程

4、總結(jié)

mysqld_safe 進(jìn)程和 mysqld 進(jìn)程是父子進(jìn)程關(guān)系
systemd 服務(wù)啟動(dòng)，kill 父進(jìn)程(會(huì)話首進(jìn)程)，會(huì)導(dǎo)致子進(jìn)程也退出
mysqld_safe 命令啟動(dòng)，kill 父進(jìn)程(非會(huì)話首進(jìn)程)，不會(huì)導(dǎo)致子進(jìn)程退出；重新啟動(dòng)父進(jìn)程，報(bào)錯(cuò)子進(jìn)程已存在
可以使用mysqld_safe命令啟動(dòng) + 改造mysqld_safe腳本，實(shí)現(xiàn)【啟、停mysqld_safe進(jìn)程，不會(huì)影響mysqld進(jìn)程】。此時(shí)不要混合使用systemd啟動(dòng)數(shù)據(jù)庫(kù)，需要維護(hù)這個(gè)特殊的mysqld_safe

責(zé)任編輯：武曉燕來(lái)源： GreatSQL社區(qū)

systemd 服務(wù)腳本