distributedlog-tutorials/distributedlog-basic/basic-4.md

Write Multi Records Atomic using Write Proxy Client

This tutorial shows how to write multi records atomic using write proxy client.

Open a write proxy client

Create write proxy client builder.

    DistributedLogClientBuilder builder = DistributedLogClientBuilder.newBuilder();
            .clientId(ClientId.apply("atomic-writer"))
            .name("atomic-writer");

Enable thrift mux.
```
    builder = builder.thriftmux(true);
```

Point the client to write proxy using finagle name.

    String finagleNameStr = "inet!127.0.0.1:8000";
    builder = builder.finagleNameStr(finagleNameStr);

Build the write proxy client.

    DistributedLogClient client = builder.build();

Write Records

Create a RecordSet for multiple records. The RecordSet has initial 16KB buffer and its compression codec is NONE.
```
    LogRecordSet.Writer recordSetWriter = LogRecordSet.newWriter(16 * 1024, Type.NONE);
```

Write multiple records into the RecordSet.

    for (String msg : messages) {
        ByteBuffer msgBuf = ByteBuffer.wrap(msg.getBytes(UTF_8));
        Promise<DLSN> writeFuture = new Promise<DLSN>();
        recordSetWriter.writeRecord(msgBuf, writeFuture);
    }

Write the RecordSet to a stream.

    String streamName = "basic-stream-8";
    Future<DLSN> writeFuture = client.writeRecordSet(streamName, recordSetWriter);

    writeFuture.addEventListener(new FutureEventListener<DLSN>() {
        @Override
        public void onFailure(Throwable cause) {
            // executed when write failed.
            recordSetWriter.abortTransmit(cause);
        }

        @Override
        public void onSuccess(DLSN value) {
            // executed when write completed.
            recordSetWriter.completeTransmit(
                    dlsn.getLogSegmentSequenceNo(),
                    dlsn.getEntryId(),
                    dlsn.getSlotId());
        }
    });

Close the write proxy client

Close the write proxy client after usage.
```
    client.close();
```

Usage

Run the example in the following steps:

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
```

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-service/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-service/conf/distributedlog_proxy.conf

Create the stream under the distributedlog uri.

    // Create Stream `basic-stream-8`
    // 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 basic-stream- -e 8

Tailing the stream using TailReader to wait for new records.

    // Tailing Stream `basic-stream-8`
    // runner run org.apache.distributedlog.basic.TailReader ${distributedlog-uri} ${stream}
    ./distributedlog-tutorials/distributedlog-basic/bin/runner run org.apache.distributedlog.basic.TailReader distributedlog://127.0.0.1:7000/messaging/distributedlog basic-stream-8

Run the example to write multiple records to the stream.

    // Write Records into Stream `basic-stream-8`
    // runner run org.apache.distributedlog.basic.AtomicWriter ${distributedlog-uri} ${stream} ${message}[, ${message}]
    ./distributedlog-tutorials/distributedlog-basic/bin/runner run org.apache.distributedlog.basic.AtomicWriter 'inet!127.0.0.1:8000' basic-stream-8 "message-1" "message-2" "message-3" "message-4" "message-5"

Example output from AtomicWriter and TailReader.

    // Output of `AtomicWriter`
    May 08, 2016 11:48:19 AM com.twitter.finagle.BaseResolver$$anonfun$resolvers$1 apply
    INFO: Resolver[inet] = com.twitter.finagle.InetResolver(com.twitter.finagle.InetResolver@6c3e459e)
    May 08, 2016 11:48:19 AM com.twitter.finagle.BaseResolver$$anonfun$resolvers$1 apply
    INFO: Resolver[fixedinet] = com.twitter.finagle.FixedInetResolver(com.twitter.finagle.FixedInetResolver@4d5698f)
    May 08, 2016 11:48:19 AM com.twitter.finagle.BaseResolver$$anonfun$resolvers$1 apply
    INFO: Resolver[neg] = com.twitter.finagle.NegResolver$(com.twitter.finagle.NegResolver$@57052dc3)
    May 08, 2016 11:48:19 AM com.twitter.finagle.BaseResolver$$anonfun$resolvers$1 apply
    INFO: Resolver[nil] = com.twitter.finagle.NilResolver$(com.twitter.finagle.NilResolver$@14ff89d7)
    May 08, 2016 11:48:19 AM com.twitter.finagle.BaseResolver$$anonfun$resolvers$1 apply
    INFO: Resolver[fail] = com.twitter.finagle.FailResolver$(com.twitter.finagle.FailResolver$@14b28d06)
    May 08, 2016 11:48:19 AM com.twitter.finagle.Init$$anonfun$1 apply$mcV$sp
    Write 'message-1' as record DLSN{logSegmentSequenceNo=1, entryId=0, slotId=0}
    Write 'message-2' as record DLSN{logSegmentSequenceNo=1, entryId=0, slotId=1}
    Write 'message-3' as record DLSN{logSegmentSequenceNo=1, entryId=0, slotId=2}
    Write 'message-4' as record DLSN{logSegmentSequenceNo=1, entryId=0, slotId=3}
    Write 'message-5' as record DLSN{logSegmentSequenceNo=1, entryId=0, slotId=4}


    // Output of `TailReader`
    Opening log stream basic-stream-8
    Log stream basic-stream-8 is empty.
    Wait for records starting from DLSN{logSegmentSequenceNo=1, entryId=0, slotId=0}
    Received record DLSN{logSegmentSequenceNo=1, entryId=0, slotId=0}
    """
    message-1
    """
    Received record DLSN{logSegmentSequenceNo=1, entryId=0, slotId=1}
    """
    message-2
    """
    Received record DLSN{logSegmentSequenceNo=1, entryId=0, slotId=2}
    """
    message-3
    """
    Received record DLSN{logSegmentSequenceNo=1, entryId=0, slotId=3}
    """
    message-4
    """
    Received record DLSN{logSegmentSequenceNo=1, entryId=0, slotId=4}
    """
    message-5
    """