Re: Making external calls from a FlinkKafkaPartitioner

[Ron Crocker]

Thanks Nico -

Thanks for the feedback, and nice catch on the missing volatile. 

Ron
—
Ron Crocker
Principal Engineer & Architect
( ( •)) New Relic
rcroc...@newrelic.com
M: +1 630 363 8835

> On Nov 3, 2017, at 7:48 AM, Nico Kruber  wrote:
> 
> Hi Ron,
> imho your code should be fine (except for a potential visibility problem on 
> the 
> changes of the non-volatile partitionMap member, depending on your needs).
> 
> The #open() method should be called (once) for each sink initialization 
> (according to the javadoc) and then you should be fine with the asynchronous 
> updater thread.
> I'm including Gordon (cc'd) just to be sure as he may know more.
> 
> 
> Nico
> 
> On Friday, 3 November 2017 04:06:02 CET Ron Crocker wrote:
>> We have a system where the Kafka partition a message should go into is a
>> function of a value in the message. Often, it’s value % # partitions, but
>> for some values it’s not - it’s a specified list of partitions that changes
>> over time. Our “simple Java library” that produces messages for this system
>> also has a background thread that periodically polls a HTTP endpoint (at a
>> rate of 1/minute as its default) to refresh that list of special cases.
>> 
>> It’s easy to create a FlinkKafkaPartitioner that does the mod operation;
>> what I’m not so sure about is how to get this polling operation into the
>> partitioner. I’m about to try it the obvious way (create a background
>> thread that polls the URL and updates the partition map), but I wonder if
>> that’s actually going to cause a bunch of problems for the Flink runtime.
>> 
>> Here’s the code that I have right now:
>> public class EventInsertPartitioner extends KafkaPartitioner> String>> { private final String partitionerURL;
>>private final long updateIntervalInMillis;
>>private Map partitionMap;
>>private ScheduledExecutorService executor;
>> 
>>public EventInsertPartitioner(String partitionerURL, long
>> updateIntervalInMillis) { this.partitionerURL = partitionerURL;
>>this.updateIntervalInMillis = updateIntervalInMillis;
>>this.partitionMap = new HashMap<>();
>>}
>> 
>>@Override
>>public void open(int parallelInstanceId, int parallelInstances, int[]
>> partitions) { executor = Executors.newScheduledThreadPool(1);
>>executor.scheduleAtFixedRate(
>>() -> updatePartitionMapRunnable(),
>>updateIntervalInMillis,
>>updateIntervalInMillis,
>>TimeUnit.MILLISECONDS);
>> 
>>}
>> 
>>private void updatePartitionMapRunnable() {
>>// Make synchronous request to partitionerURL
>>// This is a simple JSON that matches our data
>>String response = "{1:[1,2,3],2:[2]}";
>>// Replace current partitionMap with new HashMap from the response
>>this.partitionMap = convertResponseToMap(response);
>>// Replacing the current value of partitionMap with the updated
>> version doesn't // require synchronization
>>}
>> 
>>private Map convertResponseToMap(String response) {
>> Map hashMap = new HashMap<>();
>>// Convert response to JSON structure and just use that?
>>// or Iterate and add to local hashMap
>>return hashMap;
>>}
>> 
>>@Override
>>public int partition(Tuple2 next, byte[] serializedKey,
>> byte[] serializedValue, int numPartitions) { long myKey = next.f0;
>> 
>>if (partitionMap.containsKey(myKey)) {
>>List partitions = partitionMap.get(myKey);
>>myKey =
>> partitions.get(ThreadLocalRandom.current().nextInt(partitions.size())); }
>> 
>>return (int)(myKey % numPartitions);
>>}
>> }
>> Ron
>> —
>> Ron Crocker
>> Principal Engineer & Architect
>> ( ( •)) New Relic
>> rcroc...@newrelic.com
>> M: +1 630 363 8835

Re: Making external calls from a FlinkKafkaPartitioner

[Nico Kruber]

Hi Ron,
imho your code should be fine (except for a potential visibility problem on the 
changes of the non-volatile partitionMap member, depending on your needs).

The #open() method should be called (once) for each sink initialization 
(according to the javadoc) and then you should be fine with the asynchronous 
updater thread.
I'm including Gordon (cc'd) just to be sure as he may know more.


Nico

On Friday, 3 November 2017 04:06:02 CET Ron Crocker wrote:
> We have a system where the Kafka partition a message should go into is a
> function of a value in the message. Often, it’s value % # partitions, but
> for some values it’s not - it’s a specified list of partitions that changes
> over time. Our “simple Java library” that produces messages for this system
> also has a background thread that periodically polls a HTTP endpoint (at a
> rate of 1/minute as its default) to refresh that list of special cases.
> 
> It’s easy to create a FlinkKafkaPartitioner that does the mod operation;
> what I’m not so sure about is how to get this polling operation into the
> partitioner. I’m about to try it the obvious way (create a background
> thread that polls the URL and updates the partition map), but I wonder if
> that’s actually going to cause a bunch of problems for the Flink runtime.
> 
> Here’s the code that I have right now:
> public class EventInsertPartitioner extends KafkaPartitioner String>> { private final String partitionerURL;
> private final long updateIntervalInMillis;
> private Map partitionMap;
> private ScheduledExecutorService executor;
> 
> public EventInsertPartitioner(String partitionerURL, long
> updateIntervalInMillis) { this.partitionerURL = partitionerURL;
> this.updateIntervalInMillis = updateIntervalInMillis;
> this.partitionMap = new HashMap<>();
> }
> 
> @Override
> public void open(int parallelInstanceId, int parallelInstances, int[]
> partitions) { executor = Executors.newScheduledThreadPool(1);
> executor.scheduleAtFixedRate(
> () -> updatePartitionMapRunnable(),
> updateIntervalInMillis,
> updateIntervalInMillis,
> TimeUnit.MILLISECONDS);
> 
> }
> 
> private void updatePartitionMapRunnable() {
> // Make synchronous request to partitionerURL
> // This is a simple JSON that matches our data
> String response = "{1:[1,2,3],2:[2]}";
> // Replace current partitionMap with new HashMap from the response
> this.partitionMap = convertResponseToMap(response);
> // Replacing the current value of partitionMap with the updated
> version doesn't // require synchronization
> }
> 
> private Map convertResponseToMap(String response) {
> Map hashMap = new HashMap<>();
> // Convert response to JSON structure and just use that?
> // or Iterate and add to local hashMap
> return hashMap;
> }
> 
> @Override
> public int partition(Tuple2 next, byte[] serializedKey,
> byte[] serializedValue, int numPartitions) { long myKey = next.f0;
> 
> if (partitionMap.containsKey(myKey)) {
> List partitions = partitionMap.get(myKey);
> myKey =
> partitions.get(ThreadLocalRandom.current().nextInt(partitions.size())); }
> 
> return (int)(myKey % numPartitions);
> }
> }
> Ron
> —
> Ron Crocker
> Principal Engineer & Architect
> ( ( •)) New Relic
> rcroc...@newrelic.com
> M: +1 630 363 8835

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Making external calls from a FlinkKafkaPartitioner

[Ron Crocker]

We have a system where the Kafka partition a message should go into is a 
function of a value in the message. Often, it’s value % # partitions, but for 
some values it’s not - it’s a specified list of partitions that changes over 
time. Our “simple Java library” that produces messages for this system also has 
a background thread that periodically polls a HTTP endpoint (at a rate of 
1/minute as its default) to refresh that list of special cases.

It’s easy to create a FlinkKafkaPartitioner that does the mod operation; what 
I’m not so sure about is how to get this polling operation into the 
partitioner. I’m about to try it the obvious way (create a background thread 
that polls the URL and updates the partition map), but I wonder if that’s 
actually going to cause a bunch of problems for the Flink runtime.

Here’s the code that I have right now:
public class EventInsertPartitioner extends KafkaPartitioner> {
private final String partitionerURL;
private final long updateIntervalInMillis;
private Map partitionMap;
private ScheduledExecutorService executor;

public EventInsertPartitioner(String partitionerURL, long 
updateIntervalInMillis) {
this.partitionerURL = partitionerURL;
this.updateIntervalInMillis = updateIntervalInMillis;
this.partitionMap = new HashMap<>();
}

@Override
public void open(int parallelInstanceId, int parallelInstances, int[] 
partitions) {
executor = Executors.newScheduledThreadPool(1);
executor.scheduleAtFixedRate(
() -> updatePartitionMapRunnable(),
updateIntervalInMillis,
updateIntervalInMillis,
TimeUnit.MILLISECONDS);

}

private void updatePartitionMapRunnable() {
// Make synchronous request to partitionerURL
// This is a simple JSON that matches our data
String response = "{1:[1,2,3],2:[2]}";
// Replace current partitionMap with new HashMap from the response
this.partitionMap = convertResponseToMap(response); 
// Replacing the current value of partitionMap with the updated version 
doesn't
// require synchronization
}

private Map convertResponseToMap(String response) {
Map hashMap = new HashMap<>();
// Convert response to JSON structure and just use that?
// or Iterate and add to local hashMap
return hashMap;
}

@Override
public int partition(Tuple2 next, byte[] serializedKey, 
byte[] serializedValue, int numPartitions) {
long myKey = next.f0;

if (partitionMap.containsKey(myKey)) {
List partitions = partitionMap.get(myKey);
myKey = 
partitions.get(ThreadLocalRandom.current().nextInt(partitions.size()));
}

return (int)(myKey % numPartitions);
}
}
Ron
—
Ron Crocker
Principal Engineer & Architect
( ( •)) New Relic
rcroc...@newrelic.com
M: +1 630 363 8835