uniqe:ever window emits many duplicates. is this a bug ? or is something wrong with the script ?

[rzorzorzo]

Description:
unique:ever window emits unexpectedly many duplicats

Affected Siddhi Version:
siddhi-tooling-5.1.0
OS, DB, other environment details and versions:
win 10
Steps to reproduce:
@app:name("RaceRank")

@app:description("Description of the plan")

@sink(type='log', prefix='IN')
@source(
type='kafka',
topic.list='kafka_waypoint_topic',
partition.no.list='0',
threading.option='single.thread',
group.id='group',
is.binary.message='true',
bootstrap.servers='localhost:9092',
@Map(type = 'json'))
define stream RaceWaypointStream (timestamp long, lineId string, waypointId string, vehicleId string);

@sink(type='log', prefix='MID')
define stream RankStream(lineId string, ranking string, vehicleId string, timestamp long);

@sink(type='log', prefix='OUT')
-- @sink(type='kafka',
-- topic='kafka_rank_topic',
-- is.binary.message='true',
-- bootstrap.servers='localhost:9092',
-- is.synchronous='true',
-- @Map(type = 'json')
-- )
define stream RankOutStream(timestamp long, lineId string, sortedRank string);

@purge(enable='true', interval='10 sec', idle.period='1 min')
partition with ( lineId of RaceWaypointStream )
begin
from RaceWaypointStream
select lineId, str:concat(waypointId, '$', convert(timestamp,'string'), '$', vehicleId,'$',lineId) as ranking, vehicleId, timestamp
insert into RankStream;

from RankStream#window.unique:ever(vehicleId)

-- select timestamp, lineId, convert(list:sort(list:collect(ranking), 'DESC'), 'string') as sortedRank
select timestamp, lineId, ranking as sortedRank
insert into RankOutStream;
end;

a producer with 100 kafka-producers running each in a thread produce 1 events per 10 ms. all events have different content.

as output we first see
that the loggers log in the expected order:
IN, MID, OUT, IN, MID, OUT, ....
at some point we see:
OUT, OUT, OUT, ... with the same event being duplicated up to 50-80x which is causing a congestion of the test system.

Question: is this an issue with the script ? or a bug ?

Related Issues: