GDB调试MySQL

在学习Oracle的时候使用GDB调试，主要是关于学习Oracle的闩锁原理，那么，为什么要用GDB调试MySQL：
1.识别故障 2.场景重现 3.创建测试案例确认BUG 4.定位缺陷根源 5.测试和创建补丁修复BUG
1、安装编译MySQL需要的软件包 yum install -y cmake make gcc gcc-c++ ncurses-devel bison gdb 2、编译MySQL # git clone https://github.com/mysql/mysql-server.git # cd mysql-server # git checkout mysql-5.7.19 # cd BUILD; cmake .. -DDOWNLOAD_BOOST=1 -DWITH_DEBUG=1 -DWITH_UNIT_TESTS=off # make # make install 3、连接MySQL程序 3.1、查看MySQL进程ID
[root@debug ~]# ps -ef | grep mysql root     24589     1  0 07:58 ?        00:00:00 /bin/sh /usr/local/mysql/bin/mysqld_safe --basedir=/usr/local/mysql --datadir=/usr/local/mysql/data --user=mysql mysql    24794 24589  0 07:58 ?        00:00:01 /usr/local/mysql/bin/mysqld --basedir=/usr/local/mysql --datadir=/usr/local/mysql/data --plugin-dir=/usr/local/mysql/lib/plugin --user=mysql --log-error=/usr/local/mysql/data/mysql-debug.log --pid-file=debug.pid --socket=/tmp/mysql.sock --port=3306 root     25009 24993  0 11:29 pts/2    00:00:00 grep mysql
GNU gdb (GDB) Red Hat Enterprise Linux (7.2-92.el6) Copyright (C) 2010 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later http://gnu.org/licenses/gpl.html 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: http://www.gnu.org/software/gdb/bugs/ . (gdb) attach 24794 Attaching to process 24794 Reading symbols from /usr/local/mysql/bin/mysqld...done. Reading symbols from /lib64/libpthread.so.0...(no debugging symbols found)...done. [New LWP 24969] [New LWP 24824] [New LWP 24821] [New LWP 24820] [New LWP 24819] [New LWP 24818] [New LWP 24817] [New LWP 24816] [New LWP 24815] [New LWP 24814] [New LWP 24813] [New LWP 24812] [New LWP 24811] [New LWP 24810] [New LWP 24809] [New LWP 24808] [New LWP 24806] [New LWP 24805] [New LWP 24804] [New LWP 24803] [New LWP 24802] [New LWP 24801] [New LWP 24800] [New LWP 24799] [New LWP 24798] [New LWP 24797] [New LWP 24796] [New LWP 24795] [Thread debugging using libthread_db enabled] Loaded symbols for /lib64/libpthread.so.0 Reading symbols from /lib64/libcrypt.so.1...(no debugging symbols found)...done. Loaded symbols for /lib64/libcrypt.so.1 Reading symbols from /lib64/libdl.so.2...(no debugging symbols found)...done. Loaded symbols for /lib64/libdl.so.2 Reading symbols from /lib64/librt.so.1...(no debugging symbols found)...done. Loaded symbols for /lib64/librt.so.1 Reading symbols from /usr/lib64/libstdc++.so.6...(no debugging symbols found)...done. Loaded symbols for /usr/lib64/libstdc++.so.6 Reading symbols from /lib64/libm.so.6...(no debugging symbols found)...done. Loaded symbols for /lib64/libm.so.6 Reading symbols from /lib64/libgcc_s.so.1...(no debugging symbols found)...done. Loaded symbols for /lib64/libgcc_s.so.1 Reading symbols from /lib64/libc.so.6...(no debugging symbols found)...done. Loaded symbols for /lib64/libc.so.6 Reading symbols from /lib64/ld-linux-x86-64.so.2...(no debugging symbols found)...done. Loaded symbols for /lib64/ld-linux-x86-64.so.2 Reading symbols from /lib64/libfreebl3.so...(no debugging symbols found)...done. Loaded symbols for /lib64/libfreebl3.so Reading symbols from /lib64/libnss_files.so.2...(no debugging symbols found)...done. Loaded symbols for /lib64/libnss_files.so.2 0x00007f8801dfd383 in poll () from /lib64/libc.so.6 Missing separate debuginfos, use: debuginfo-install glibc-2.12-1.209.el6_9.2.x86_64 libgcc-4.4.7-18.el6.x86_64 libstdc++-4.4.7-18.el6.x86_64 nss-softokn-freebl-3.14.3-23.el6_7.x86_64
(gdb) b Sql_cmd_insert::mysql_insert Breakpoint 1 at 0x17bd1b9: file /root/mysql-server/sql/sql_insert.cc, line 423.
#0  0x00007f8801dfd383 in poll () from /lib64/libc.so.6 #1  0x00000000016c1155 in Mysqld_socket_listener::listen_for_connection_event (this=0x45d8870)     at /root/mysql-server/sql/conn_handler/socket_connection.cc:852 #2  0x0000000000ece89c in Connection_acceptor Mysqld_socket_listener ::connection_event_loop (this=0x45b5ec0)     at /root/mysql-server/sql/conn_handler/connection_acceptor.h:66 #3  0x0000000000ec6226 in mysqld_main (argc=17, argv=0x3ab4248) at /root/mysql-server/sql/mysqld.cc:5045 #4  0x0000000000ebd2d4 in main (argc=9, argv=0x7fffb2aa7408) at /root/mysql-server/sql/main.cc:25
4.4、在设置了断点之后，在另一个session2中登录数据库，发现无法登录，hung住了，在gdb中执行next（执行下一步代码），可以看到在socket_connection.cc源码第859行无法继续，代码大致是说要获取系统的socket，还有一些监听信息，由于太多了，直接在gdb中执行continue（到下一个可执行的代码），此时session2已经登录成功。
which has no line number information. Mysqld_socket_listener::listen_for_connection_event (this=0x45d8870) at /root/mysql-server/sql/conn_handler/socket_connection.cc:859 859       if (retval 0 socket_errno != SOCKET_EINTR) (gdb) n 871       if (retval 0 || abort_loop) (gdb) n 876       MYSQL_SOCKET listen_sock= MYSQL_INVALID_SOCKET; (gdb) n 877       bool is_unix_socket= false; (gdb) n 879       for (uint i= 0; i m_socket_map.size(); ++i) (gdb) n 881         if (m_poll_info.m_fds[i].revents POLLIN) (gdb) n 879       for (uint i= 0; i m_socket_map.size(); ++i) (gdb) n 881         if (m_poll_info.m_fds[i].revents POLLIN) (gdb) n 883           listen_sock= m_poll_info.m_pfs_fds[i]; (gdb) n 884           is_unix_socket= m_socket_map[listen_sock]; (gdb) n 885           break; (gdb) n 904       for (uint retry= 0; retry MAX_ACCEPT_RETRY; retry++) (gdb) n 906         socket_len_t length= sizeof(struct sockaddr_storage); (gdb) n 908                                           (struct sockaddr *)( cAddr), length); (gdb) n 909         if (mysql_socket_getfd(connect_sock) != INVALID_SOCKET || (gdb) n … ... (gdb) c Continuing.
[root@localhost:(none)][11:41:15am] MySQL- use test; Reading table information for completion of table and column names You can turn off this feature to get a quicker startup with -A Database changed [root@localhost:test][11:49:12am] MySQL- show tables; +----------------+ | Tables_in_test | +----------------+ | t              | | t1             | +----------------+ 2 rows in set (0.00 sec) [root@localhost:test][11:49:16am] MySQL- select * from t; +------+------+ | id   | name | +------+------+ |    1 | aaa  | |    2 | aaa  | |    3 | aaa  | |    4 | aaa  | +------+------+ 4 rows in set (0.00 sec)
4.6、session2做insert操作的时候，又一次hung住了，session1打印出了断点的信息，在mysql_insert：423行，直到执行continue，session2才能正常插入数据。 (gdb) c Continuing. [Switching to Thread 0x7f87e00b4700 (LWP 24824)] Breakpoint 1, Sql_cmd_insert::mysql_insert (this=0x7f87f40147b8, thd=0x7f87f401bc60, table_list=0x7f87f4013fe0)     at /root/mysql-server/sql/sql_insert.cc:423 423       DBUG_ENTER("mysql_insert"); (gdb) n 425       LEX *const lex= thd- (gdb) n 427       bool err= true; (gdb) c Continuing.
最后我想简单说一下我的MySQL调试环境的搭建，但是在此之前不得不简单说一下什么是线程，因为如果不解释一下什么是线程，简单的调试可能都会有阻碍，同时了解线程对我们普通DBA诊断性能问题也有极大的帮助。
GDB 调试 Mysql 实战（一）源码编译安装 git clone https://github.com/mysql/mysql-server.git cd mysql-server git checkout 5.7 yum install -y cmake make gcc gcc-c++ ncurses-dev...
【从入门到放弃-MySQL】CLion调试MySQL8.0源码 想对的MySQL底层实现做一些了解，奈何没有用过C++不知道怎么调试一个大型项目，一日和大神交流时大神扔给我了一份《XCode调试MySQL8秘籍》。于是在几经波折（主要是因为菜）之后终于打开了MySQL的调试大门。