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MySQL如何创建和删除临时表_MySQL

程序员文章站 2022-06-08 16:40:54
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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

摘自 记录成长之路

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