flink-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Sujit Sakre <sujit.sa...@northgateps.com>
Subject Sliding Event Time Window Processing: Window Function inconsistent behavior
Date Mon, 09 Jan 2017 16:57:15 GMT

We are using Sliding Event Time Window with Kafka Consumer. The window size
is 6 minutes, and slide is 2 minutes. We have written a window function to
select a particular window out of multiple windows for a keyed stream, e.g.
we select about 16 windows out of multiple windows for the keyed stream
based on a particular condition.

Upon a normal execution, we get 16 windows for processing inside the
condition (in window function mentioned). These windows we are putting in
different files, named after window start and end times.

the code is as below:

Calling code

public class RealTimeProcessingSlidingWindow{

public static void main(String[] args) throws Exception {

// set up the execution environment
StreamExecutionEnvironment env = StreamExecutionEnvironment.


// configure the Kafka consumer
Properties kafkaProps = new Properties();
kafkaProps.setProperty("zookeeper.connect", LOCAL_ZOOKEEPER_HOST);
kafkaProps.setProperty("bootstrap.servers", LOCAL_KAFKA_BROKER);
kafkaProps.setProperty("group.id", DEMO_GROUP);
// always read the Kafka topic from the start
kafkaProps.setProperty("auto.offset.reset" ,"earliest");

                FlinkKafkaConsumer09<Tuple5<String, String, Float, Float,
String>> consumer = new FlinkKafkaConsumer09<>(
"test",            // kafka topic name
new dataSchema(),
                DataStream<Tuple5<String, String, Float, Float, String>>
stream1 = env.addSource(consumer);
                DataStream<Tuple5<String, String, Float, Float, String>>
keyedStream = stream1.assignTimestampsAndWatermarks(new

.window(SlidingEventTimeWindows.of(Time.minutes6), Time.minutes(2)))   // 6
min window with 2 min sliding window
.apply(new CustomSlidingWindowFunction());

                env.execute("Sliding Event Time Window Processing");


public static class CustomSlidingWindowFunction implements
WindowFunction<Tuple5<String, String, Float, Float, String>, Tuple5<String,
String, Float, Float, String>, Tuple, TimeWindow>{

public void apply(Tuple key, TimeWindow window, Iterable<Tuple5<String,
String, Float, Float, String>> input,
Collector<Tuple5<String, String, Float, Float, String>> out) throws
Exception {

HashMap<String, Tuple5<String, String, Float, Float, String>> windowMap=
new HashMap<String,Tuple5<String, String, Float, Float, String>>();
for (Tuple5<String, String, Float, Float, String> wr: input){
windowMap.put(wr.f1.toString().trim(), wr);


SimpleDateFormat sf = new SimpleDateFormat(IndianDateTimeFormat);

Tuple5<String, String, Float, Float, String> t = (Tuple5<String, String,
Float, Float, String>) windowMap.get(tk);

Date d = sf.parse(t.f0.trim());


                                // Condition for selecting a window
if(d.after(x) && d.before(y)){
// Write the window output to separate files named after window Lat and Lon
writeWindowToFile(t, window, input);

// Get the buffered writer
private static synchronized BufferedWriter getWriter(String fileName)
throws IOException{
return new BufferedWriter(new FileWriter(fileName, true));
// Writes an entire window to file for the records in that window
private static synchronized void writeWindowToFile(Tuple5<String, String,
Float, Float, String> target, TimeWindow window, Iterable<Tuple5<String,
String, Float, Float, String>> input) throws IOException{
// Create a file to write a window to
String fileName = target.f2.toString() + "-" + target.f3.toString()+".csv";
BufferedWriter br = getWriter(fileName);

// Iterate and put the records in file
for (Tuple5<String, String, Float, Float, String> tr: input){
br.write(tr.f1.toString().trim()+", "+
tr.f0+", "+tr.f2+", "+tr.f3+'\n');
// flush the writer and close it

We have written the code to be threadsafe while creating and writing to file

In this code, If we execute the code multiple times on the Kafka Stream
(with certain records) most times we get 16 files with corresponding window
records, which is the correct behavior.

However sometimes only 4 files get created or 1 file or any number less
than 16 gets created randomly, this is anomalous behavior.

What could be the cause of such behavior? How do we resolve this?

Please, could you identify and suggest a solution/s.


*Sujit Sakre*

This email is sent on behalf of Northgate Public Services (UK) Limited and 
its associated companies including Rave Technologies (India) Pvt Limited 
(together "Northgate Public Services") and is strictly confidential and 
intended solely for the addressee(s). 
If you are not the intended recipient of this email you must: (i) not 
disclose, copy or distribute its contents to any other person nor use its 
contents in any way or you may be acting unlawfully;  (ii) contact 
Northgate Public Services immediately on +44(0)1908 264500 quoting the name 
of the sender and the addressee then delete it from your system.
Northgate Public Services has taken reasonable precautions to ensure that 
no viruses are contained in this email, but does not accept any 
responsibility once this email has been transmitted.  You should scan 
attachments (if any) for viruses.

Northgate Public Services (UK) Limited, registered in England and Wales 
under number 00968498 with a registered address of Peoplebuilding 2, 
Peoplebuilding Estate, Maylands Avenue, Hemel Hempstead, Hertfordshire, HP2 
4NN.  Rave Technologies (India) Pvt Limited, registered in India under 
number 117068 with a registered address of 2nd Floor, Ballard House, Adi 
Marzban Marg, Ballard Estate, Mumbai, Maharashtra, India, 400001.

View raw message