This patch adds verification of the connection with the client during the execution of the SQL query. The feature enables using the GUC variable ‘client_connection_check_interval’. The default check interval is 1 second. If you set the value of ‘client_connection_check_interval’ to 0, then the check will not be performed. The feature will be useful in cases when, during the execution of a very long query, the client suddenly terminates the connection - this will allow backend to cancel further execution of the query and free server resources.