1   How to write records to multiple streams using a load balancer

If applications does not care about ordering and they just want use multiple streams to transform messages, it is easier to use a load balancer to balancing the writes among the multiple streams.

This tutorial shows how to build a multi-streams writer, which ues a finagle load balancer to balancing traffic among multiple streams.

1.1   Make writing to a stream as a finagle service

In order to leverage the finagle load balancer to balancing traffic among multiple streams, we have to make writing to a stream as a finagle service.

class StreamWriter<VALUE> extends Service<VALUE, DLSN> {

    private final String stream;
    private final DistributedLogClient client;

    StreamWriter(String stream,
                 DistributedLogClient client) {
        this.stream = stream;
        this.client = client;
    }

    @Override
    public Future<DLSN> apply(VALUE request) {
        return client.write(stream, ByteBuffer.wrap(request.toString().getBytes(UTF_8)));
    }
}

1.2   Create a load balancer from multiple streams

1.2.1   Create a ServiceFactory

Create a set of finagle ServiceFactory over multiple streams.

String[] streams;
Set<ServiceFactory<VALUE, DLSN>> serviceFactories = Sets.newHashSet();
for (String stream : streams) {
    Service<VALUE, DLSN> service = new StreamWriter(stream, client);
    serviceFactories.add(new SingletonFactory<VALUE, DLSN>(service));
}

1.2.2   Create the load balancer

Service<VALUE, DLSN> writeSerivce =
    Balancers.heap(new scala.util.Random(System.currentTimeMillis()))
        .newBalancer(
                Activity.value(scalaSet),
                NullStatsReceiver.get(),
                new NoBrokersAvailableException("No partitions available")
        ).toService();

1.3   Write records

Once the balancer service is initialized, we can write records through the balancer service.

Future<DLSN> writeFuture = writeSerivce.write(...);

1.4   Run the tutorial

Run the example in the following steps:

1.4.1   Start the local bookkeeper cluster

You can use follow command to start the distributedlog stack locally. After the distributedlog cluster is started, you could access it using distributedlog uri distributedlog://127.0.0.1:7000/messaging/distributedlog.

// dlog local ${zk-port}
./distributedlog-core/bin/dlog local 7000

1.4.2   Start the write proxy

Start the write proxy, listening on port 8000.

// DistributedLogServerApp -p ${service-port} --shard-id ${shard-id} -sp ${stats-port} -u {distributedlog-uri} -mx -c ${conf-file}
./distributedlog-proxy-server/bin/dlog org.apache.distributedlog.service.DistributedLogServerApp -p 8000 --shard-id 1 -sp 8001 -u distributedlog://127.0.0.1:7000/messaging/distributedlog -mx -c ${distributedlog-repo}/distributedlog-proxy-server/conf/distributedlog_proxy.conf

1.4.3   Create the stream

Create the stream under the distributedlog uri.

// Create Stream `messaging-stream-{1,5}`
// dlog tool create -u ${distributedlog-uri} -r ${stream-prefix} -e ${stream-regex}
./distributedlog-core/bin/dlog tool create -u distributedlog://127.0.0.1:7000/messaging/distributedlog -r messaging-stream- -e 1-5

1.4.4   Tail the streams

Tailing the streams using MultiReader to wait for new records.

// Tailing Stream `messaging-stream-{1,5}`
// runner run org.apache.distributedlog.basic.MultiReader ${distributedlog-uri} ${stream}[, ${stream}]
./distributedlog-tutorials/distributedlog-basic/bin/runner run org.apache.distributedlog.basic.MultiReader distributedlog://127.0.0.1:7000/messaging/distributedlog messaging-stream-1,messaging-stream-2,messaging-stream-3,messaging-stream-4,messaging-stream-5

1.4.5   Write records

Run the example to write records to multiple stream in a console.

// Write Records into Stream `messaging-stream-{1,5}`
// runner run org.apache.distributedlog.messaging.ConsoleProxyRRMultiWriter ${distributedlog-uri} ${stream}[, ${stream}]
./distributedlog-tutorials/distributedlog-messaging/bin/runner run org.apache.distributedlog.messaging.ConsoleProxyRRMultiWriter 'inet!127.0.0.1:8000' messaging-stream-1,messaging-stream-2,messaging-stream-3,messaging-stream-4,messaging-stream-5

1.4.6   Check the results

Example output from ConsoleProxyRRMultiWriter and MultiReader.

// Output of `ConsoleProxyRRMultiWriter`
Picked up JAVA_TOOL_OPTIONS: -Dfile.encoding=utf8
May 08, 2016 1:22:35 PM com.twitter.finagle.BaseResolver$$anonfun$resolvers$1 apply
INFO: Resolver[inet] = com.twitter.finagle.InetResolver(com.twitter.finagle.InetResolver@6c4cbf96)
May 08, 2016 1:22:35 PM com.twitter.finagle.BaseResolver$$anonfun$resolvers$1 apply
INFO: Resolver[fixedinet] = com.twitter.finagle.FixedInetResolver(com.twitter.finagle.FixedInetResolver@57052dc3)
May 08, 2016 1:22:35 PM com.twitter.finagle.BaseResolver$$anonfun$resolvers$1 apply
INFO: Resolver[neg] = com.twitter.finagle.NegResolver$(com.twitter.finagle.NegResolver$@14ff89d7)
May 08, 2016 1:22:35 PM com.twitter.finagle.BaseResolver$$anonfun$resolvers$1 apply
INFO: Resolver[nil] = com.twitter.finagle.NilResolver$(com.twitter.finagle.NilResolver$@14b28d06)
May 08, 2016 1:22:35 PM com.twitter.finagle.BaseResolver$$anonfun$resolvers$1 apply
INFO: Resolver[fail] = com.twitter.finagle.FailResolver$(com.twitter.finagle.FailResolver$@56488f87)
May 08, 2016 1:22:35 PM com.twitter.finagle.Init$$anonfun$1 apply$mcV$sp
INFO: Finagle version media-platform-tools/release-20160330-1117-sgerstein-9-g2dcdd6c (rev=2dcdd6c866f9bd3599ed49568d651189735e8ad6) built at 20160330-160058
[dlog] > message-1
[dlog] > message-2
[dlog] > message-3
[dlog] > message-4
[dlog] > message-5
[dlog] >


// Output of `MultiReader`
Opening log stream messaging-stream-1
Opening log stream messaging-stream-2
Opening log stream messaging-stream-3
Opening log stream messaging-stream-4
Opening log stream messaging-stream-5
Log stream messaging-stream-2 is empty.
Wait for records from messaging-stream-2 starting from DLSN{logSegmentSequenceNo=1, entryId=0, slotId=0}
Open reader to read records from stream messaging-stream-2
Log stream messaging-stream-1 is empty.
Wait for records from messaging-stream-1 starting from DLSN{logSegmentSequenceNo=1, entryId=0, slotId=0}
Open reader to read records from stream messaging-stream-1
Log stream messaging-stream-3 is empty.
Wait for records from messaging-stream-3 starting from DLSN{logSegmentSequenceNo=1, entryId=0, slotId=0}
Open reader to read records from stream messaging-stream-3
Log stream messaging-stream-4 is empty.
Wait for records from messaging-stream-4 starting from DLSN{logSegmentSequenceNo=1, entryId=0, slotId=0}
Open reader to read records from stream messaging-stream-4
Log stream messaging-stream-5 is empty.
Wait for records from messaging-stream-5 starting from DLSN{logSegmentSequenceNo=1, entryId=0, slotId=0}
Open reader to read records from stream messaging-stream-5
Received record DLSN{logSegmentSequenceNo=1, entryId=2, slotId=0} from stream messaging-stream-3
"""
message-1
"""
Received record DLSN{logSegmentSequenceNo=1, entryId=2, slotId=0} from stream messaging-stream-2
"""
message-2
"""
Received record DLSN{logSegmentSequenceNo=1, entryId=4, slotId=0} from stream messaging-stream-2
"""
message-3
"""
Received record DLSN{logSegmentSequenceNo=1, entryId=2, slotId=0} from stream messaging-stream-4
"""
message-4
"""
Received record DLSN{logSegmentSequenceNo=1, entryId=6, slotId=0} from stream messaging-stream-2
"""
message-5
"""