官网连接:
https://dev.mysql.com/doc/refman/8.0/en/server-system-variables.htmlhttp://www.cndba.cn/hbhe0316/article/22621

这个变量设置用户创建的MEMORY表允许增长的最大大小。该变量的值用于计算内存表MAX_ROWS值。设置这个变量对任何现有的MEMORY表都没有影响，除非用CREATE table这样的语句重新创建表，或者用ALTER table或TRUNCATE table修改表。服务器重启还将现有MEMORY表的最大大小设置为全局max_heap_table_size值。

这个变量设置用户创建的MEMORY引擎表允许增长的最大大小；
该变量的值用于计算内存表的MAX_ROWS值;
设置这个变量对一个已有的MEMORY表没有影响;
这个变量与tmp_table_size一起使用，以限制内部内存表的大小。http://www.cndba.cn/hbhe0316/article/22621

1.查看默认大小http://www.cndba.cn/hbhe0316/article/22621

mysql> show variables like 'max_heap_table_size';
+---------------------+----------+
| Variable_name       | Value    |
+---------------------+----------+
| max_heap_table_size | 16777216 |
+---------------------+----------+
1 row in set (0.00 sec)

2.修改global级别

mysql> set global max_heap_table_size=32*1024*1024;
Query OK, 0 rows affected (0.00 sec)

mysql> quit
Bye
[root@mysql57 ~]# /mysql/bin/mysql -uroot -pwwwwww -S /mysql/mysql.sock
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor.  Commands end with ; or /g.
Your MySQL connection id is 3
Server version: 5.7.36-log MySQL Community Server (GPL)

Copyright (c) 2000, 2021, Oracle and/or its affiliates.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '/h' for help. Type '/c' to clear the current input statement.

mysql> show variables like 'max_heap_table_size';
+---------------------+----------+
| Variable_name       | Value    |
+---------------------+----------+
| max_heap_table_size | 33554432 |
+---------------------+----------+
1 row in set (0.00 sec)

3.修改/etc/my.cnf文件http://www.cndba.cn/hbhe0316/article/22621

[root@mysql57 ~]# cat /etc/my.cnf | grep -i max-heap-table-size
max-heap-table-size= 32M
[root@mysql57 ~]# service mysqld restart
Shutting down MySQL.... SUCCESS! 
Starting MySQL.. SUCCESS!

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