兰州传诚网络科技有限公司,外贸建站优化,永久网站空间,绵阳 网站建设原创 张政俊 老叶茶馆来自专辑MySQL修行作者#xff1a;张政俊就职于中欧基金#xff0c;知数堂粉丝#xff0c;数据库爱好者#xff0c;熟悉RDBMS、nosql、new sql等各类数据库。啃完Oreilly的《高性能mysql》、姜老师的《MySQL技术内幕》#xff0c;再加上个2,3年的实战…原创 张政俊 老叶茶馆来自专辑MySQL修行作者张政俊就职于中欧基金知数堂粉丝数据库爱好者熟悉RDBMS、nosql、new sql等各类数据库。啃完Oreilly的《高性能mysql》、姜老师的《MySQL技术内幕》再加上个2,3年的实战经验就基本可以成为一名能独立处理问题的DBA了。但有些时候遇到些很刁钻的疑难杂症的话那就束手无策了。所以要想技术水平更进一步的话源码调试是避不开的。GDB 简介GDB 是 Linux 系统中非常常见的调试工具它有以下功能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.常用的参数命令info threads查看全部线程thread n指定某个线程b在某处打断点c继续往下走s执行一行代码如果代码函数调用则进入函数n执行一行代码函数调用不进入p打印某个变量值list打印代码的文本信息bt查看某个线程的栈帧info b查看当前所有断点信息调试环境搭建直接在 linux 下面使用 gdb这种应该是目前市面上最简单有效的方式。1. 安装gdbyum install -y cmake make gcc gcc-c ncurses-devel bison gdb2. 下载、解压源码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. 安装数据库cmake -DCMAKE_INSTALL_PREFIX/gdb/mysql/ -DMYSQL_DATADIR/gdb/data/ -DSYSCONFDIR/gdb/mysql/ -DWITH_INNOBASE_STORAGE_ENGINE1 -DWITH_ARCHIVE_STORAGE_ENGINE1 -DWITH_BLACKHOLE_STORAGE_ENGINE1 -DWITH_FEDERATED_STORAGE_ENGINE1 -DWITH_PARTITION_STORAGE_ENGINE1 -DMYSQL_UNIX_ADDR/gdb/mysql/mysql3.sock -DMYSQL_TCP_PORT3306 -DENABLED_LOCAL_INFILE1 -DEXTRA_CHARSETSall -DDEFAULT_CHARSETutf8 -DDEFAULT_COLLATIONutf8_general_ci -DMYSQL_USERmysql -DWITH_BINLOG_PREALLOCON -DWITH_BOOST/gdb/mysql-5.7.25/boost/boost_1_59_0 -DWITH_DEBUG1-DWITH_DEBUG1 是最关键的它的作用是开启DBUGmakemake install4. 初始化数据库vim /etc/my.cnf #简易配置下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_names1 innodb_buffer_pool_size300M log-binmysql-bin character_set_serverutf8 binlog_formatrow datadir/gdb/data log-error /gdb/data/error.log pid-file /gdb/data/mysql.pid innodb_log_file_size512M innodb_log_files_in_group 3 sql_mode autocommit1 server-id 1 max_connections1500 wait_timeout70 interactive_timeout70 skip-name-resolve [mysqldump] quick max_allowed_packet 16M [myisamchk] key_buffer_size 20M sort_buffer_size 20M read_buffer 2M write_buffer 2M5. 启动数据库赋权以便mysql用户有权限在该目录下生成文件chown -R mysql:mysql /gdb/data初始化数据库命令cd /gdb/mysql/bin./mysqld --initialize --usermysql --basedir/gdb/mysql --datadir/gdb/data启动数据库cd /gdb/mysql/support-files ./mysql.server startinsert 断点调试1. 查看 mysql 进程 id[rootops sql]# ps aux | grep mysqlroot 629 0.0 0.0 112724 972 pts/2 S 14:52 0:00 grep -E --colorauto 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 --usermysql --log-error/gdb/data/error.log --pid-file/gdb/data/mysql.pid --socket/gdb/data/mysqld.sock --port3306可以看到此时mysql的进程号为209262. gdb 中 attach mysql 进程[rootops ~]# 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 copyingand 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. 找到断点这次看的是 insert 插入的流程找到 sql_insert.cc 文件源码中的函数为Sql_cmd_insert::mysql_insert4. 设置断点(gdb) b Sql_cmd_insert::mysql_insertBreakpoint 1 at 0x175aed9: file /gdb/mysql-5.7.25/sql/sql_insert.cc, line 423.然后查看下线程的栈帧(gdb) bt#0 0x00002b15ce803f0d in poll () from /lib64/libc.so.6#1 0x0000000001667f87 in Mysqld_socket_listener::listen_for_connection_event (this0x3967430) at /gdb/mysql-5.7.25/sql/conn_handler/socket_connection.cc:852#2 0x0000000000eb15cc in Connection_acceptor::connection_event_loop (this0x4f882e0) at /gdb/mysql-5.7.25/sql/conn_handler/connection_acceptor.h:66#3 0x0000000000ea904a in mysqld_main (argc38, argv0x383c248) at /gdb/mysql-5.7.25/sql/mysqld.cc:5149#4 0x0000000000ea01bd in main (argc9, argv0x7ffc73765b88) at /gdb/mysql-5.7.25/sql/main.cc:255. 数据库登陆gdb断点设置完后起个新的数据库连接会发现此时无法登陆在gdb中执行next(gdb) nSingle stepping until exit from function poll,which has no line number information.Mysqld_socket_listener::listen_for_connection_event (this0x3967430) at /gdb/mysql-5.7.25/sql/conn_handler/socket_connection.cc:859859 if (retval 0 socket_errno ! SOCKET_EINTR)通过输出可以知道数据库处于获取系统 socket 状态。接下来需要跳过的步骤有些多我们直接使用 continue (直接到下一段可执行代码)(gdb) cContinuing.新起客户端连接成功[rootops 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.mysql6. 数据库插入插入操作前切换schema和查询都是没问题的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)插入一条 id3 的数据出现了等待mysql insert into test values (3);7. 分析断点信息断点触发如下(gdb) cContinuing.[Switching to Thread 0x2b15faf02700 (LWP 21617)]Breakpoint 1, Sql_cmd_insert::mysql_insert (this0x2b1614008348, thd0x2b1614003af0, table_list0x2b1614007db8) at /gdb/mysql-5.7.25/sql/sql_insert.cc:423423 DBUG_ENTER(mysql_insert);bt 命令展示栈帧(gdb) bt#0 Sql_cmd_insert::mysql_insert (this0x2b1614008348, thd0x2b1614003af0, table_list0x2b1614007db8) at /gdb/mysql-5.7.25/sql/sql_insert.cc:423#1 0x000000000176256e in Sql_cmd_insert::execute (this0x2b1614008348, thd0x2b1614003af0) at /gdb/mysql-5.7.25/sql/sql_insert.cc:3118#2 0x000000000153b093 in mysql_execute_command (thd0x2b1614003af0, first_leveltrue) at /gdb/mysql-5.7.25/sql/sql_parse.cc:3596#3 0x0000000001540820 in mysql_parse (thd0x2b1614003af0, parser_state0x2b15faf01690) at /gdb/mysql-5.7.25/sql/sql_parse.cc:5570#4 0x0000000001536131 in dispatch_command (thd0x2b1614003af0, com_data0x2b15faf01df0, commandCOM_QUERY) at /gdb/mysql-5.7.25/sql/sql_parse.cc:1484#5 0x0000000001534f9a in do_command (thd0x2b1614003af0) at /gdb/mysql-5.7.25/sql/sql_parse.cc:1025#6 0x00000000016658dc in handle_connection (arg0x39610f0) at /gdb/mysql-5.7.25/sql/conn_handler/connection_handler_per_thread.cc:306#7 0x0000000001ced592 in pfs_spawn_thread (arg0x5508e50) 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接下来输入 n 会逐行输出我们这里直接 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)发布一个特殊版本的mysql有些函数所在源码的位置比较好理解比如上面的 insert 功能或者 delete 功能。是不是可以通过修改 delete 函数打包一个数据永不会被删除的 mysql 呢定位函数位置先追踪mysql进程(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_64delete函数这里打上断点(gdb) b Sql_cmd_delete::mysql_deleteBreakpoint 1 at 0x175198b: file /gdb/mysql-5.7.25/sql/sql_delete.cc, line 50.数据库执行delete语句触发断点mysql delete from test where id 3;gbk断点信息Breakpoint 1, Sql_cmd_delete::mysql_delete (this0x2b16040020c8, thd0x2b1604007e30, limit18446744073709551615) at /gdb/mysql-5.7.25/sql/sql_delete.cc:5050 DBUG_ENTER(mysql_delete);查看相关栈帧#0 Sql_cmd_delete::mysql_delete (this0x2b16040020c8, thd0x2b1604007e30, limit18446744073709551615) at /gdb/mysql-5.7.25/sql/sql_delete.cc:50#1 0x0000000001755cc6 in Sql_cmd_delete::execute (this0x2b16040020c8, thd0x2b1604007e30) at /gdb/mysql-5.7.25/sql/sql_delete.cc:1392#2 0x000000000153b12f in mysql_execute_command (thd0x2b1604007e30, first_leveltrue) at /gdb/mysql-5.7.25/sql/sql_parse.cc:3606#3 0x0000000001540820 in mysql_parse (thd0x2b1604007e30, parser_state0x2b15faf43690) at /gdb/mysql-5.7.25/sql/sql_parse.cc:5570#4 0x0000000001536131 in dispatch_command (thd0x2b1604007e30, com_data0x2b15faf43df0, commandCOM_QUERY) at /gdb/mysql-5.7.25/sql/sql_parse.cc:1484#5 0x0000000001534f9a in do_command (thd0x2b1604007e30) at /gdb/mysql-5.7.25/sql/sql_parse.cc:1025#6 0x00000000016658dc in handle_connection (arg0x54b6510) at /gdb/mysql-5.7.25/sql/conn_handler/connection_handler_per_thread.cc:306#7 0x0000000001ced592 in pfs_spawn_thread (arg0x5508e50) 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修改源码可以看到 #1 是 Sql_cmd_delete::execute 这个就是 delete 处理的函数去源代码中找到相应函数把正真实现删除逻辑的代码给注释掉返回的 res 值直接赋成 truebool 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);/*注释以下删除逻辑的代码*//* 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编译mysql启动后就会发现delete语句无法删除数据了。调试总结如果想深入学习源码就可以从栈帧出发但是这是基于知道函数接口功能的前提下进行的如果不知道某个功能会调用什么函数断点调试就很难进行了。直接去读完 mysql 所有源码成本太高而且 mysql 的代码结构并不友好耗时耗力不值得。最好的方案还是遇到问题时或针对特殊的一个功能点按需去寻找函数入口然后逐步深入分析。希望这篇文章可以帮到想接触mysql源码调试的同学以后我遇到特殊的问题也会通过gdb去调试涉及的相关函数大家可以持续关注~全文完。Enjoy MySQL :)
