原創 張政俊 老葉茶館

來自專輯

MySQL修行

作者：張政俊

就職于中歐基金，知數堂粉絲，數據庫愛好者，熟悉RDBMS、nosql、new sql等各類數據庫。

啃完O'reilly的《高性能mysql》、姜老師的《MySQL技術內幕》，再加上個2,3年的實戰經驗，就基本可以成為一名能獨立處理問題的DBA了。但有些時候遇到些很刁鉆的疑難雜癥的話，那就束手無策了。

所以要想技術水平更進一步的話，源碼調試是避不開的。

GDB 簡介

GDB 是 Linux 系統中，非常常見的調試工具，它有以下功能：

• Start your program, specifying anything that might affect its behavior.
• Make your program stop on specified conditions.
• Examine what has happened, when your program has stopped.
• Change things in your program, so you can experiment with correcting the effects of one bug and go on to learn about another.

常用的參數命令：

• info threads：查看全部線程
• thread n：指定某個線程
• b：在某處打斷點
• c：繼續往下走
• s：執行一行代碼，如果代碼函數調用，則進入函數
• n：執行一行代碼，函數調用不進入
• p：打印某個變量值
• list：打印代碼的文本信息
• bt：查看某個線程的棧幀
• info b：查看當前所有斷點信息

調試環境搭建

直接在 linux 下面使用 gdb，這種應該是目前市面上最簡單有效的方式。

1. 安裝gdb

yum install -y cmake make gcc gcc-c++ ncurses-devel bison gdb

2. 下載、解壓源碼

wget https://dev.mysql.com/get/Downloads/MySQL-5.7/mysql-boost-5.7.25.tar.gztar zxvf mysql-boost-5.7.25.tar.gzmkdir -p /gdb/mysql/mkdir -p /gdb/data/

3. 安裝數據庫

cmake -DCMAKE_INSTALL_PREFIX=/gdb/mysql/ -DMYSQL_DATADIR=/gdb/data/ -DSYSCONFDIR=/gdb/mysql/ -DWITH_INNOBASE_STORAGE_ENGINE=1 -DWITH_ARCHIVE_STORAGE_ENGINE=1 -DWITH_BLACKHOLE_STORAGE_ENGINE=1 -DWITH_FEDERATED_STORAGE_ENGINE=1 -DWITH_PARTITION_STORAGE_ENGINE=1 -DMYSQL_UNIX_ADDR=/gdb/mysql/mysql3.sock -DMYSQL_TCP_PORT=3306 -DENABLED_LOCAL_INFILE=1 -DEXTRA_CHARSETS=all -DDEFAULT_CHARSET=utf8 -DDEFAULT_COLLATION=utf8_general_ci -DMYSQL_USER=mysql -DWITH_BINLOG_PREALLOC=ON -DWITH_BOOST=/gdb/mysql-5.7.25/boost/boost_1_59_0 -DWITH_DEBUG=1

-DWITH_DEBUG=1 是最關鍵的，它的作用是開啟DBUG

make&&make install

4. 初始化數據庫

vim /etc/my.cnf #簡易配置下my.cnf文件 [client] port = 3306 socket = /gdb/data/mysqld.sock [mysqld] port = 3306 socket =/gdb/data/mysqld.sock skip-external-locking key_buffer_size = 8M max_allowed_packet = 1M table_open_cache = 64 sort_buffer_size = 512K net_buffer_length = 8K read_buffer_size = 128K read_rnd_buffer_size = 256K myisam_sort_buffer_size = 8M lower_case_table_names=1 innodb_buffer_pool_size=300M log-bin=mysql-bin character_set_server=utf8 binlog_format=row datadir=/gdb/data log-error =/gdb/data/error.log pid-file = /gdb/data/mysql.pid innodb_log_file_size=512M innodb_log_files_in_group = 3 sql_mode='' autocommit=1 server-id = 1 max_connections=1500 wait_timeout=70 interactive_timeout=70 skip-name-resolve [mysqldump] quick max_allowed_packet = 16M [myisamchk] key_buffer_size = 20M sort_buffer_size = 20M read_buffer = 2M write_buffer = 2M

5. 啟動數據庫

賦權，以便mysql用戶有權限在該目錄下生成文件：
chown -R mysql:mysql /gdb/data

初始化數據庫命令：

cd /gdb/mysql/bin./mysqld --initialize --user=mysql --basedir=/gdb/mysql --datadir=/gdb/data

啟動數據庫：

cd /gdb/mysql/support-files ./mysql.server start

insert 斷點調試

1. 查看 mysql 進程 id

[root@ops sql]# ps aux | grep mysqlroot 629 0.0 0.0 112724 972 pts/2 S+ 14:52 0:00 grep -E --color=auto mysqlroot 20926 0.0 0.0 113312 1628 pts/0 S 11:15 0:00 /bin/sh /gdb/mysql/bin/mysqld_safe --datadir=/gdb/data --pid-file=/gdb/data/mysql.pidmysql 21357 0.0 5.8 1740820 223820 pts/0 Sl 11:15 0:01 /gdb/mysql/bin/mysqld --basedir=/gdb/mysql --datadir=/gdb/data --plugin-dir=/gdb/mysql/lib/plugin --user=mysql --log-error=/gdb/data/error.log --pid-file=/gdb/data/mysql.pid --socket=/gdb/data/mysqld.sock --port=3306

可以看到此時mysql的進程號為：20926

2. gdb 中 attach mysql 進程

[root@ops ~]# gdbGNU gdb (GDB) Red Hat Enterprise Linux 7.6.1-119.el7Copyright (C) 2013 Free Software Foundation, Inc.License GPLv3+: GNU GPL version 3 or later This is free software: you are free to change and redistribute it.There is NO WARRANTY, to the extent permitted by law. Type "show copying"and "show warranty" for details.This GDB was configured as "x86_64-redhat-linux-gnu".For bug reporting instructions, please see:.(gdb) attach 21357Attaching to process 21357Reading symbols from /gdb/mysql/bin/mysqld...done.Reading symbols from /lib64/libpthread.so.0...(no debugging symbols found)...done.[New LWP 21617][New LWP 21387][New LWP 21386][New LWP 21384][New LWP 21383][New LWP 21382][New LWP 21381][New LWP 21380][New LWP 21379][New LWP 21378][New LWP 21377][New LWP 21376][New LWP 21375][New LWP 21374][New LWP 21373][New LWP 21369][New LWP 21368][New LWP 21367][New LWP 21366][New LWP 21365][New LWP 21364][New LWP 21363][New LWP 21362][New LWP 21361][New LWP 21360][New LWP 21359][New LWP 21358][Thread debugging using libthread_db enabled]Using host libthread_db library "/lib64/libthread_db.so.1".Loaded symbols for /lib64/libpthread.so.0Reading symbols from /lib64/libcrypt.so.1...(no debugging symbols found)...done.Loaded symbols for /lib64/libcrypt.so.1Reading symbols from /lib64/libdl.so.2...(no debugging symbols found)...done.Loaded symbols for /lib64/libdl.so.2Reading symbols from /lib64/librt.so.1...(no debugging symbols found)...done.Loaded symbols for /lib64/librt.so.1Reading symbols from /lib64/libstdc++.so.6...(no debugging symbols found)...done.Loaded symbols for /lib64/libstdc++.so.6Reading symbols from /lib64/libm.so.6...(no debugging symbols found)...done.Loaded symbols for /lib64/libm.so.6Reading symbols from /lib64/libgcc_s.so.1...(no debugging symbols found)...done.Loaded symbols for /lib64/libgcc_s.so.1Reading symbols from /lib64/libc.so.6...(no debugging symbols found)...done.Loaded symbols for /lib64/libc.so.6Reading symbols from /lib64/ld-linux-x86-64.so.2...(no debugging symbols found)...done.Loaded symbols for /lib64/ld-linux-x86-64.so.2Reading symbols from /lib64/libfreebl3.so...Reading symbols from /lib64/libfreebl3.so...(no debugging symbols found)...done.(no debugging symbols found)...done.Loaded symbols for /lib64/libfreebl3.soReading symbols from /lib64/libnss_files.so.2...(no debugging symbols found)...done.Loaded symbols for /lib64/libnss_files.so.2Reading symbols from /lib64/libnss_sss.so.2...Reading symbols from /lib64/libnss_sss.so.2...(no debugging symbols found)...done.(no debugging symbols found)...done.Loaded symbols for /lib64/libnss_sss.so.20x00002b15ce803f0d in poll () from /lib64/libc.so.6Missing separate debuginfos, use: debuginfo-install glibc-2.17-222.el7.x86_64 libgcc-4.8.5-39.el7.x86_64 libstdc++-4.8.5-39.el7.x86_64 nss-softokn-freebl-3.34.0-2.el7.x86_64 sssd-client-1.16.0-19.el7.x86_64(gdb)

3. 找到斷點

這次看的是 insert 插入的流程，找到 sql_insert.cc 文件：

源碼中的函數為：Sql_cmd_insert::mysql_insert

4. 設置斷點

(gdb) b Sql_cmd_insert::mysql_insertBreakpoint 1 at 0x175aed9: file /gdb/mysql-5.7.25/sql/sql_insert.cc, line 423.

然后查看下線程的棧幀：

(gdb) bt#0 0x00002b15ce803f0d in poll () from /lib64/libc.so.6#1 0x0000000001667f87 in Mysqld_socket_listener::listen_for_connection_event (this=0x3967430) at /gdb/mysql-5.7.25/sql/conn_handler/socket_connection.cc:852#2 0x0000000000eb15cc in Connection_acceptor::connection_event_loop (this=0x4f882e0) at /gdb/mysql-5.7.25/sql/conn_handler/connection_acceptor.h:66#3 0x0000000000ea904a in mysqld_main (argc=38, argv=0x383c248) at /gdb/mysql-5.7.25/sql/mysqld.cc:5149#4 0x0000000000ea01bd in main (argc=9, argv=0x7ffc73765b88) at /gdb/mysql-5.7.25/sql/main.cc:25

5. 數據庫登陸

gdb斷點設置完后，起個新的數據庫連接：

會發現此時無法登陸，在gdb中執行next：

(gdb) nSingle stepping until exit from function poll,which has no line number information.Mysqld_socket_listener::listen_for_connection_event (this=0x3967430) at /gdb/mysql-5.7.25/sql/conn_handler/socket_connection.cc:859859 if (retval < 0 && socket_errno != SOCKET_EINTR)

通過輸出可以知道數據庫處于獲取系統 socket 狀態。接下來需要跳過的步驟有些多，我們直接使用 continue (直接到下一段可執行代碼)

(gdb) cContinuing.

新起客戶端連接成功：

[root@ops bin]# mysql -uroot -pEnter password:Welcome to the MySQL monitor. Commands end with ; or g.Your MySQL connection id is 14Server version: 5.7.25-debug-log Source distributionType 'help;' or 'h' for help. Type 'c' to clear the current input statement.mysql>

6. 數據庫插入

插入操作前，切換schema和查詢都是沒問題的：

mysql> use gdbDatabase changedmysql> show tables;+---------------+| Tables_in_gdb |+---------------+| test |+---------------+1 row in set (0.00 sec)mysql> select * from test;+------+| id |+------+| 1 || 2 |+------+2 rows in set (0.00 sec)

插入一條 id=3 的數據，出現了等待：

mysql> insert into test values (3);

7. 分析斷點信息

斷點觸發，如下：

(gdb) cContinuing.[Switching to Thread 0x2b15faf02700 (LWP 21617)]Breakpoint 1, Sql_cmd_insert::mysql_insert (this=0x2b1614008348, thd=0x2b1614003af0, table_list=0x2b1614007db8) at /gdb/mysql-5.7.25/sql/sql_insert.cc:423423 DBUG_ENTER("mysql_insert");

bt 命令展示棧幀：

(gdb) bt#0 Sql_cmd_insert::mysql_insert (this=0x2b1614008348, thd=0x2b1614003af0, table_list=0x2b1614007db8) at /gdb/mysql-5.7.25/sql/sql_insert.cc:423#1 0x000000000176256e in Sql_cmd_insert::execute (this=0x2b1614008348, thd=0x2b1614003af0) at /gdb/mysql-5.7.25/sql/sql_insert.cc:3118#2 0x000000000153b093 in mysql_execute_command (thd=0x2b1614003af0, first_level=true) at /gdb/mysql-5.7.25/sql/sql_parse.cc:3596#3 0x0000000001540820 in mysql_parse (thd=0x2b1614003af0, parser_state=0x2b15faf01690) at /gdb/mysql-5.7.25/sql/sql_parse.cc:5570#4 0x0000000001536131 in dispatch_command (thd=0x2b1614003af0, com_data=0x2b15faf01df0, command=COM_QUERY) at /gdb/mysql-5.7.25/sql/sql_parse.cc:1484#5 0x0000000001534f9a in do_command (thd=0x2b1614003af0) at /gdb/mysql-5.7.25/sql/sql_parse.cc:1025#6 0x00000000016658dc in handle_connection (arg=0x39610f0) at /gdb/mysql-5.7.25/sql/conn_handler/connection_handler_per_thread.cc:306#7 0x0000000001ced592 in pfs_spawn_thread (arg=0x5508e50) at /gdb/mysql-5.7.25/storage/perfschema/pfs.cc:2190#8 0x00002b15cd699e25 in start_thread () from /lib64/libpthread.so.0#9 0x00002b15ce80ebad in clone () from /lib64/libc.so.6

接下來輸入 n 會逐行輸出，我們這里直接 continue，阻塞的 insert 也完成了：

mysql> insert into test values (3);Query OK, 1 row affected (2 min 49.57 sec)

發布一個特殊版本的mysql

有些函數所在源碼的位置比較好理解，比如上面的 insert 功能，或者 delete 功能。是不是可以通過修改 delete 函數，打包一個數據永不會被刪除的 mysql 呢？

定位函數位置

先追蹤mysql進程：

(gdb) attach 21357Attaching to process 21357Reading symbols from /gdb/mysql/bin/mysqld...done.Reading symbols from /lib64/libpthread.so.0...(no debugging symbols found)...done.[New LWP 5584][New LWP 5583][New LWP 21617][New LWP 21387][New LWP 21386][New LWP 21384][New LWP 21383][New LWP 21382][New LWP 21381][New LWP 21380][New LWP 21379][New LWP 21378][New LWP 21377][New LWP 21376][New LWP 21375][New LWP 21374][New LWP 21373][New LWP 21369][New LWP 21368][New LWP 21367][New LWP 21366][New LWP 21365][New LWP 21364][New LWP 21363][New LWP 21362][New LWP 21361][New LWP 21360][New LWP 21359][New LWP 21358][Thread debugging using libthread_db enabled]Using host libthread_db library "/lib64/libthread_db.so.1".Loaded symbols for /lib64/libpthread.so.0Reading symbols from /lib64/libcrypt.so.1...(no debugging symbols found)...done.Loaded symbols for /lib64/libcrypt.so.1Reading symbols from /lib64/libdl.so.2...(no debugging symbols found)...done.Loaded symbols for /lib64/libdl.so.2Reading symbols from /lib64/librt.so.1...(no debugging symbols found)...done.Loaded symbols for /lib64/librt.so.1Reading symbols from /lib64/libstdc++.so.6...(no debugging symbols found)...done.Loaded symbols for /lib64/libstdc++.so.6Reading symbols from /lib64/libm.so.6...(no debugging symbols found)...done.Loaded symbols for /lib64/libm.so.6Reading symbols from /lib64/libgcc_s.so.1...(no debugging symbols found)...done.Loaded symbols for /lib64/libgcc_s.so.1Reading symbols from /lib64/libc.so.6...(no debugging symbols found)...done.Loaded symbols for /lib64/libc.so.6Reading symbols from /lib64/ld-linux-x86-64.so.2...(no debugging symbols found)...done.Loaded symbols for /lib64/ld-linux-x86-64.so.2Reading symbols from /lib64/libfreebl3.so...Reading symbols from /lib64/libfreebl3.so...(no debugging symbols found)...done.(no debugging symbols found)...done.Loaded symbols for /lib64/libfreebl3.soReading symbols from /lib64/libnss_files.so.2...(no debugging symbols found)...done.Loaded symbols for /lib64/libnss_files.so.2Reading symbols from /lib64/libnss_sss.so.2...Reading symbols from /lib64/libnss_sss.so.2...(no debugging symbols found)...done.(no debugging symbols found)...done.Loaded symbols for /lib64/libnss_sss.so.20x00002b15ce803f0d in poll () from /lib64/libc.so.6Missing separate debuginfos, use: debuginfo-install glibc-2.17-222.el7.x86_64 libgcc-4.8.5-39.el7.x86_64 libstdc++-4.8.5-39.el7.x86_64 nss-softokn-freebl-3.34.0-2.el7.x86_64 sssd-client-1.16.0-19.el7.x86_64

delete函數這里打上斷點：

(gdb) b Sql_cmd_delete::mysql_deleteBreakpoint 1 at 0x175198b: file /gdb/mysql-5.7.25/sql/sql_delete.cc, line 50.

數據庫執行delete語句觸發斷點：

mysql> delete from test where id =3;

gbk斷點信息：

Breakpoint 1, Sql_cmd_delete::mysql_delete (this=0x2b16040020c8, thd=0x2b1604007e30, limit=18446744073709551615) at /gdb/mysql-5.7.25/sql/sql_delete.cc:5050 DBUG_ENTER("mysql_delete");

查看相關棧幀：

#0 Sql_cmd_delete::mysql_delete (this=0x2b16040020c8, thd=0x2b1604007e30, limit=18446744073709551615) at /gdb/mysql-5.7.25/sql/sql_delete.cc:50#1 0x0000000001755cc6 in Sql_cmd_delete::execute (this=0x2b16040020c8, thd=0x2b1604007e30) at /gdb/mysql-5.7.25/sql/sql_delete.cc:1392#2 0x000000000153b12f in mysql_execute_command (thd=0x2b1604007e30, first_level=true) at /gdb/mysql-5.7.25/sql/sql_parse.cc:3606#3 0x0000000001540820 in mysql_parse (thd=0x2b1604007e30, parser_state=0x2b15faf43690) at /gdb/mysql-5.7.25/sql/sql_parse.cc:5570#4 0x0000000001536131 in dispatch_command (thd=0x2b1604007e30, com_data=0x2b15faf43df0, command=COM_QUERY) at /gdb/mysql-5.7.25/sql/sql_parse.cc:1484#5 0x0000000001534f9a in do_command (thd=0x2b1604007e30) at /gdb/mysql-5.7.25/sql/sql_parse.cc:1025#6 0x00000000016658dc in handle_connection (arg=0x54b6510) at /gdb/mysql-5.7.25/sql/conn_handler/connection_handler_per_thread.cc:306#7 0x0000000001ced592 in pfs_spawn_thread (arg=0x5508e50) at /gdb/mysql-5.7.25/storage/perfschema/pfs.cc:2190#8 0x00002b15cd699e25 in start_thread () from /lib64/libpthread.so.0#9 0x00002b15ce80ebad in clone () from /lib64/libc.so.6

修改源碼

可以看到 #1 是 Sql_cmd_delete::execute ，這個就是 delete 處理的函數，去源代碼中找到相應函數：

把正真實現刪除邏輯的代碼給注釋掉，返回的 res 值直接賦成 true：

bool Sql_cmd_delete::execute(THD *thd){ DBUG_ASSERT(thd->lex->sql_command == SQLCOM_DELETE); LEX *const lex= thd->lex; SELECT_LEX *const select_lex= lex->select_lex; SELECT_LEX_UNIT *const unit= lex->unit; TABLE_LIST *const first_table= select_lex->get_table_list(); TABLE_LIST *const all_tables= first_table; if (delete_precheck(thd, all_tables)) return true; DBUG_ASSERT(select_lex->offset_limit == 0); unit->set_limit(select_lex); /* Push ignore / strict error handler */ Ignore_error_handler ignore_handler; Strict_error_handler strict_handler; if (thd->lex->is_ignore()) thd->push_internal_handler(&ignore_handler); else if (thd->is_strict_mode()) thd->push_internal_handler(&strict_handler);/*注釋以下刪除邏輯的代碼*//* MYSQL_DELETE_START(const_cast(thd->query().str)); bool res = mysql_delete(thd, unit->select_limit_cnt); MYSQL_DELETE_DONE(res, (ulong) thd->get_row_count_func());*//*直接返回true*/ bool res =true; /* Pop ignore / strict error handler */if (thd->lex->is_ignore() || thd->is_strict_mode()) thd->pop_internal_handler(); return res;}

然后上文的方法去重新編譯mysql，啟動后就會發現delete語句無法刪除數據了。

調試總結

如果想深入學習源碼，就可以從棧幀出發，但是這是基于知道函數接口功能的前提下進行的，如果不知道某個功能會調用什么函數，斷點調試就很難進行了。

直接去讀完 mysql 所有源碼，成本太高，而且 mysql 的代碼結構并不友好，耗時耗力不值得。最好的方案還是遇到問題時或針對特殊的一個功能點按需去尋找函數入口，然后逐步深入分析。

希望這篇文章可以幫到想接觸mysql源碼調試的同學，以后我遇到特殊的問題也會通過gdb去調試涉及的相關函數，大家可以持續關注~

全文完。

Enjoy MySQL :)

總結

以上是生活随笔為你收集整理的dev c++调试怎么看变量的值_利用GDB调试 MSQL的全部內容，希望文章能夠幫你解決所遇到的問題。

如果覺得生活随笔網站內容還不錯，歡迎將生活随笔推薦給好友。