MySQL Bugs: #99002: Suggest warn user not use more than 64K connections in mysql doc

Bug #99002	Suggest warn user not use more than 64K connections in mysql doc
Submitted:	20 Mar 2020 8:18	Modified:	20 Mar 2020 18:11
Reporter:	Fungo Wang (OCA)	Email Updates:
Status:	Not a Bug	Impact on me:	None
Category:	MySQL Server: Documentation	Severity:	S3 (Non-critical)
Version:	5.7, 8.0	OS:	Any
Assigned to:		CPU Architecture:	Any
Tags:	100K, 64K, max_connections

Description:
https://dev.mysql.com/doc/refman/8.0/en/server-system-variables.html#sysvar_max_connection...
https://dev.mysql.com/doc/refman/5.7/en/server-system-variables.html#sysvar_max_connection...

Default Value   151
Minimum Value   1
Maximum Value   100000

In the mysql doc, the max value of max_connections is 100K, but actually 
1. for 8.0, it only reach to 64K (refer bug #98624),  
2. for 5.7, it cause data issue after 64K in 5.7 (refer bug #98911), this is much more dangerous than mysqld crash for a database product.

So I guess we'd better warn the user don't use more than 64K connections in the 5.7/8.0 mysql doc (most user won't scan the mysql bug list regularly).

How to repeat:
Check the bugs and doc, then think about the mysql users. :)

Suggested fix:
Add warning in doc about 64K connections.

Thank you for the bug report.

Posted by developer:

re: "
In the mysql doc, the max value of max_connections is 100K, but actually
1. for 8.0, it only reach to 64K (refer bug #98624),
"

max_connections can in fact be set to 100000, as documented:

mysql> set global max_connections=100000;
Query OK, 0 rows affected (0.00 sec)

mysql> select @@max_connections;
+-------------------+
| @@max_connections |
+-------------------+
|            100000 |
+-------------------+
1 row in set (0.00 sec)

So the documentation is accurate. If a large value leads to problematic
behavior, that's a server issue, to be dealt with in the course of the other
bug that you filed (thanks for doing so).

re: "
2. for 5.7, it cause data issue after 64K in 5.7 (refer bug #98911), this is
much more dangerous than mysqld crash for a database product.
"

Again, not a docs issue. If a large value leads to problematic behavior,
that's a server issue, to be dealt with in the course of the other bug that
you filed (again, thanks for doing so).

Hi Paul,

> max_connections can in fact be set to 100000, as documented:

Yes, it's true.

I won't object with you for this point, it can be set to the value as documentation.

My request is not to treat/accept this as a bug. But to add warning in the doc, to let the users know that this could lead critical issue.

There are no other way to feedback such message/request, so I filed this bug here.

Thanks.