distributedlog-tutorials/distributedlog-messaging/messaging-1.md

### How to write records to multiple streams partitioning by key

This tutorial shows how to build a multiple-partitioned writer, which writes records to streams partitioned by key.

#### Design a partitioner interface

In order to implement a multiple-partitioned writer, we need a `Partitioner` to partition the records into different
streams based on their keys. The partitioner takes a `KEY` and its total partitions to compute a partition id for the
given `KEY`.

```
    public interface Partitioner<KEY> {
            int partition(KEY key, int totalPartitions);
    }
```

#### Write records based on partition key

Once we have the `Partitioner` interface, it is easy to implement partitioned writer logic:

- Partitioner takes a `KEY` and the total number of partitions, and compute the partition id for the key.
- Use the partition id to choose the stream to write.
- Use `DistributedLogClient.write(stream, ...)` to write the data to the chosen stream.

```
    String[] streams = ...;
    int pid = partitioner.partition(key, streams.length);
    ByteBuffer value = ...;
    client.write(streams[pid], value);
```

#### Usage

Run the example in the following steps:

1.  Start the local bookkeeper cluster. After the bookkeeper 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
    ```

2.  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
    ```

3.  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
    ```

4.  Tailing the stream using `MultiReader` to read from multiple streams.
    ```
        // 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
    ```

6.  Run the example to write records to multiple stream in a console - the record should be in the form of `KEY:VALUE`.
    ```
        // Write Records into Stream `messaging-stream-{1,5}`
        // runner run org.apache.distributedlog.messaging.ConsoleProxyPartitionedMultiWriter ${distributedlog-uri} ${stream}[, ${stream}]
        ./distributedlog-tutorials/distributedlog-messaging/bin/runner run org.apache.distributedlog.messaging.ConsoleProxyPartitionedMultiWriter 'inet!127.0.0.1:8000' messaging-stream-1,messaging-stream-2,messaging-stream-3,messaging-stream-4,messaging-stream-5
    ```

7.  Example output from `ConsoleProxyPartitionedMultiWriter` and `MultiReader`.
    ```
        // Output of `ConsoleProxyPartitionedMultiWriter`
        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] > 1:value-1
        [dlog] > 2:value-2
        [dlog] > 3:value-3
        [dlog] > 4:value-4
        [dlog] > 5:value-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=0, slotId=0} from stream messaging-stream-2
        """
        value-1
        """
        Received record DLSN{logSegmentSequenceNo=1, entryId=0, slotId=0} from stream messaging-stream-3
        """
        value-2
        """
        Received record DLSN{logSegmentSequenceNo=1, entryId=0, slotId=0} from stream messaging-stream-4
        """
        value-3
        """
        Received record DLSN{logSegmentSequenceNo=1, entryId=0, slotId=0} from stream messaging-stream-5
        """
        value-4
        """
        Received record DLSN{logSegmentSequenceNo=1, entryId=0, slotId=0} from stream messaging-stream-1
        """
        value-5
        """
    ```