How to check max session count? and current session count??

• To determine the original value for the MaxClientSessions parameter:
=> SELECT CURRENT_VALUE FROM CONFIGURATION_PARAMETERS WHERE parameter_name='MaxClientSessions';

CURRENT_VALUE

50
(1 row)
• To increase the MaxClientSessions parameter to 100 (for example) do:
=> SELECT SET_CONFIG_PARAMETER('MaxClientSessions', 100);

BTW, I would expect to see an error like: "New session rejected due to limit, already 55 sessions activ"
To monitor requests for resources that are rejected by the Resource Manager do: SELECT * FROM resource_rejections;
The V_MONITOR.ERROR_MESSAGES system table tracks error and warning messages encountered while processing queries.
SELECT event_timestamp, user_name, message FROM error_messages ORDER BY event_timestamp DESC;
and check also dc_errors;