1.介绍:
MySQL临时表,属于session级别,当session退出时,临时表被删除。临时表允许与其他表同名,并单独维护在thd的结构体中;因此,不同的session可以创建同名的临时表,并且只操作自己拥有的临时表; 创建临时表的语法很简单: root@test 03:26:44>show create table tmp1\G *************************** 1. row *************************** Table: tmp1 Create Table: CREATE TEMPORARY TABLE `tmp1` ( `a` int(11) NOT NULL AUTO_INCREMENT, `b` int(11) DEFAULT NULL, `c` int(11) DEFAULT NULL, PRIMARY KEY (`a`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 1 row in set (0.00 sec) 当创建临时表后,会在tmp文件夹下生成两个文件: #sql3e95_1a_0.frm #sql3e95_1a_0.ibd 那么MySQL本身究竟是如何创建和删除临时表的呢? 2.创建 执行SQL: CREATE TEMPORARY TABLE `tmp1` ( `a` int(11) NOT NULL AUTO_INCREMENT, `b` int(11) DEFAULT NULL, `c` int(11) DEFAULT NULL, PRIMARY KEY (`a`) );
1)断点:ysql_execute_command
mysql_execute_command: 2205 switch (lex->sql_command) { (gdb) 2532 if (!(lex->create_info.options & HA_LEX_CREATE_TMP_TABLE)) (gdb) p lex->create_info.options --------if语句里为false $2 = 1 create_table_precheck------检查是否具有创建表的权限,以及表名在全局链表上是否已存在(临时表无需检查) append_file_to_dir ------Fix names if symlinked tables if (select_lex->item_list.elements) -------------------当为create ....select这样的语句时select_lex->item_list.elements为非0值,这里我们只考虑简单的情况 if ((result= new select_create)) res= handle_select(thd, lex, result, 0); else (1)mysql_create_like_table ---------------create table like...类似的语句 (2)mysql_create_table ---------------主要分析这个函数 2)断点:mysql_create_table mysql_create_table mysql_create_table_no_lock check_engine file = get_new_handler 3842 set_table_default_charset(thd, create_info, (char*) db); 3844 if (mysql_prepare_create_table(thd, create_info, alter_info, 3854 path_length= build_tmptable_filename(thd, path, sizeof(path)); -----创建临时表文件名:#sql{进程id}_{thread_id}_{当前线程的临时表整数标识thd->tmp_table} 3978 rea_create_table --------------------------------------------------------------------创建frm文件和ibd文件 3986 open_temporary_table-------------------------------------------------------------打开临时表 (1)构建table和table_share结构体 (2)将table结构体加入到thd->temporary_tables链表中 4009 error= write_create_table_bin_log----------------------------------------------写入binlog 3.删除临时表 手动执行 drop table tmp1 mysql_execute_command case SQLCOM_DROP_TABLE: mysql_rm_table mysql_rm_table_part2 for (table= tables; table; table= table->next_local) drop_temporary_table-----------------------------从thd->temporary_tables上查找临时表 调用close_temporary_table来关闭、删除临时表文件,并从thd->temporary_tables上删除相应节点 if (!drop_temporary)-------------------------------当删除的是非临时表时,执行下面的逻辑 ---------------------------------------- 4. 当session退出时。 看看堆栈: Breakpoint 16, rm_temporary_table (base=0xc8c560, path=0x1427c10 "/u01/mysql-5148.stock/tmp/#sql3e95_1d_0") at sql_base.cc:5634 5634 bool rm_temporary_table(handlerton *base, char *path) (gdb) 5641 strmov(ext= strend(path), reg_ext); (gdb) bt #0 rm_temporary_table (base=0xc8c560, path=0x1427c10 "/u01/mysql-5148.stock/tmp/#sql3e95_1d_0") at sql_base.cc:5641 #1 0x00000000005f6eaa in close_temporary (table=0x1427030, free_share=true, delete_table=true) at sql_base.cc:1928 #2 0x00000000005f725f in close_temporary_tables (thd=0x14065f0) at sql_base.cc:1549 #3 0x0000000000592d9b in THD::cleanup (this=0x14065f0) at sql_class.cc:967 #4 0x00000000005a3579 in unlink_thd (thd=0xc8c560) at mysqld.cc:1858 #5 0x00000000005a35dc in one_thread_per_connection_end (thd=0xc8c560, put_in_cache=16) at mysqld.cc:1945 #6 0x00000000005ac208 in handle_one_connection (arg=0x14065f0) at sql_connect.cc:1141 #7 0x0000003e638064a7 in start_thread () from /lib64/libpthread.so.0 #8 0x0000003e630d3c2d in clone () from /lib64/libc.so.6 #9 0x0000000000000000 in ?? () 在session结束的时候,会调用THD::cleanup来做临时表的清理工作 |
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