Thread: max_connections

max_connections

From

Joao Junior

Date:

22 October 2019, 15:28:31

Hi,

I am not sure if here is the best place to post this.

I would like to know why max_connections parameter can't be changed without a restart. I know that it is a postmaster's context parameter.

Which PostgreSQL's subsystems, structures and OS kernel parameters should be affected to support this change??

Thanks!

Re: max_connections

From

Pavel Stehule

Date:

22 October 2019, 15:39:19

út 22. 10. 2019 v 14:28 odesílatel Joao Junior <jcoj2006@gmail.com> napsal:

Hi,
I am not sure if here is the best place to post this.
I would like to know why max_connections parameter can't be changed without a restart. I know that it is a postmaster's context parameter.
Which PostgreSQL's subsystems, structures and OS kernel parameters should be affected to support this change??

The max_connections is used more time inside PostgreSQL source code - typically for dimensions arrays where one field is per session.

You can search in source code the variable "MaxConnections". It's used for informations about sessions (processes), about transactions, locks, ..

Unfortunately, lot of these arrays are allocated in shared memory. For shared memory has Postgres special coding standards - almost all memory is allocated in startup time, and newer released. It is very simple to manage memory with these rules. It is fast, and there are not any risk of memory leaks. But related limits requires restart. Usually it is not a problem. So necessity of restart after change of max_connection is related to simple but very robust share memory management.

Regards

Pavel

Thanks!