max_connections

Memory Usage

When the value of max_connections is increased, the server's memory usage can also increase, because each client connection can require additional memory on the server.

The amount of memory used by each connection depends on the values of several system variables, including, but not limited to:

• tmp_memory_table_size

• sort_buffer_size

• read_buffer_size

• join_buffer_size

• thread_stack

• binlog_cache_size

The amount of memory used by each connections also depends on the features in use by the connection, including, but not limited to:

• The number of temporary tables being used

• The complexity of the queries being executed

• The number of tables being joined by the queries

• If binary logging is enabled

PARAMETERS

SKYSQL

Show Value with SHOW VARIABLES

SHOW GLOBAL VARIABLES can show the global value:

SHOW GLOBAL VARIABLES
   LIKE 'max_connections';

Since this system variable is only global scope, SHOW VARIABLES and SHOW SESSION VARIABLES also show the global value.

Query Value using @@global and @@session

In SELECT and other SQL statements, @@global can be queried for the global value:

SELECT @@global.max_connections;

Since this system variable is only global scope, @@session can't be queried for this variable.

Information Schema

The information_schema.SYSTEM_VARIABLES table can be queried to obtain details about the system variable:

SELECT *
FROM information_schema.SYSTEM_VARIABLES
WHERE VARIABLE_NAME LIKE 'max_connections';

The information_schema.GLOBAL_VARIABLES table can be queried to obtain the global value:

SELECT *
FROM information_schema.GLOBAL_VARIABLES
WHERE VARIABLE_NAME LIKE 'max_connections';

This system variable is only global scope, so the information_schema.SESSION_VARIABLES table can also be queried to obtain the global value:

SELECT *
FROM information_schema.SESSION_VARIABLES
WHERE VARIABLE_NAME LIKE 'max_connections';