What Is the Maximum Number of Connections to an RDS DB Instance?

RDS does not have constraints on the number of connections. This number is determined by the default value and value range of the DB engine. For example, you can set max_connections and max_user_connections in a parameter template to configure the maximum number of connections for an RDS for MySQL DB instance.

Changing the Maximum Number of Connections

You can change the maximum number of connections using commands.

Query the maximum number of connections.
show global variables like 'max_connections';
Change the value of max_connections under mysqld in the my.cnf file.
[mysqld]

max_connections = 1000

Setting the Maximum Number of RDS for MySQL Connections to an Appropriate Value

In addition to the value of max_connections, the maximum number of concurrent client connections allowed by MySQL is also limited by the maximum number of files that can be opened by a single process in the operating system. For example, if the maximum number of files that can be opened by each process is set to 100 in the operating system, the max_connections parameter does not take effect even if it is set to 200.
Check the maximum number of files that can be opened by a single process in the operating system. The default value is 1024.

ulimit -n

The parameter open_files_limit indicates the maximum number of files that can be opened by a single process, which is read from the operating system during MySQL startup.

Check the value of open_files_limit.

show variables like 'open_files_limit';
Suggestions
The maximum number of MySQL connections can be customized provided that it is allowed by your instance specifications. The maximum number of connections is closely related to the instance memory. For details, see About max_connections.

In actual scenarios, set the maximum number of connections to an appropriate value because more connections lead to large resource consumption.

About max_connections

max_connections: maximum number of clients that can be connected at the same time. If this parameter is set to default, it is related to the memory (unit: GB) of the DB instance. The calculation formula is as follows:

Estimated value of max_connections = Available node memory/Estimated memory occupied by a single connection

Available node memory = Total memory – Memory occupied by the buffer pool – 1 GB (mysqld process/OS/monitoring program)
Estimated memory usage of a single connection (single_thread_memory) = thread_stack (256 KB) + binlog_cache_size (32 KB) + join_buffer_size (256 KB) + sort_buffer_size (256 KB) + read_buffer_size (128 KB) + read_rnd_buffer_size (256 KB) ≈ 1 MB

The following table lists the default values of max_connections for different memory specifications.