I have an interface which has a threshold profile for alerting when there are more than 540 discards in 5 minutes and I am polling on a 1 minute interval.

However it does not create events and it is taking lots of discards.

If an event was raised on an interface threshold, a new event will not be raised until the existing one is cleared.

Release : 3.x

Component : CA Performance Center

1. get item if of device or interface

connect to vsql on the Vertica host as the dauser, and run:
cd /opt/vertica/bin

./vsql -Udauser -wdapass (your password may vary)

/x

select * from alarm where item_id=<Item ID of device or interface>;

Are there events in this table where the clear_date =0, if so, event never cleared.

Change threshold profile rules, and change accordingly to clear old events. 
Make sure you are changing the correct threshold profile

note, for a more detailed result, you can run this query, replacing ID with the correct values for that spot.
.........

select profile_name, profile_id from alarm where profile_name like 'enter_case_sensitive_name_here';
now use the profileid for this one:

SELECT a.item_id, a.rule_id, a.profile_id, a.alarm_id FROM alarm a WHERE a.profile_id=<ID> AND a.alarm_type='Threshold' AND NOT EXISTS  (SELECT 1 FROM alarm_clear ac WHERE ac.profile_id=<ID> AND ac.alarm_type='Threshold' AND ac.alarm_id = a.alarm_id);

An event created will only be seen for 30 days before EM drops it.  In case the event never clears in 30 days.