DistributedLog

git@github.com:twitter/distributedlog.git/tree/master/
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TAGS #uses_maven
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Tail reading records from a stream

This tutorial shows how to tail read records from a stream.

Open a distributedlog manager

  • Create distributedlog URI.

    String dlUriStr = ...;
URI uri = URI.create(dlUriStr);

  • Create distributedlog configuration.

    DistributedLogConfiguration conf = new DistributedLogConfiguration();

  • Build the distributedlog namespace.

    DistributedLogNamespace namespace = DistributedLogNamespaceBuilder.newBuilder()
        .conf(conf)
        .uri(uri)
        .build();

  • Open the distributedlog manager.

    DistributedLogManager dlm = namespace.openLog("basic-stream-9");

Get Last Record

  • Get the last record from the record. From the last record, we can use DLSN of last record to start tailing the stream.

    LogRecordWithDLSN record = dlm.getLastLogRecord();
DLSN lastDLSN = record.getDlsn();

Read Records

  • Open the stream to start read the records.

    AsyncLogReader reader = FutureUtils.result(dlm.openAsyncLogReader(lastDLSN));

  • Read the next available record from the stream. The future is satisified when the record is available.

    Future<LogRecordWithDLSN> readFuture = reader.readNext();

  • Register a future listener on read completion.

    final FutureEventListener<LogRecordWithDLSN> readListener = new FutureEventListener<LogRecordWithDLSN>() {
    @Override
    public void onFailure(Throwable cause) {
        // executed when read failed.
    }

    @Override
    public void onSuccess(LogRecordWithDLSN record) {
        // process the record
        ...
        // issue read next
        reader.readNext().addEventListener(this);
    }
};
reader.readNext().addEventListener(readListener);

Close the reader

  • Close the reader after usage.

    FutureUtils.result(reader.asyncClose());

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-service/bin/dlog com.twitter.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

  3. Create the stream under the distributedlog uri.

    // Create Stream `basic-stream-9`
// 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 9

  4. Tailing the stream using TailReader to wait for new records.

    // Tailing Stream `basic-stream-9`
// runner run com.twitter.distributedlog.basic.TailReader ${distributedlog-uri} ${stream}
./distributedlog-tutorials/distributedlog-basic/bin/runner run com.twitter.distributedlog.basic.TailReader distributedlog://127.0.0.1:7000/messaging/distributedlog basic-stream-9

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

    // Write Records into Stream `basic-stream-9`
// runner run com.twitter.distributedlog.basic.ConsoleProxyWriter ${distributedlog-uri} ${stream}
./distributedlog-tutorials/distributedlog-basic/bin/runner run com.twitter.distributedlog.basic.ConsoleProxyWriter 'inet!127.0.0.1:8000' basic-stream-9

  6. Example output from ConsoleProxyWriter and TailReader.

    // Output of `ConsoleProxyWriter`
May 08, 2016 10:27:41 AM com.twitter.finagle.BaseResolver$$anonfun$resolvers$1 apply
INFO: Resolver[inet] = com.twitter.finagle.InetResolver(com.twitter.finagle.InetResolver@756d7bba)
May 08, 2016 10:27:41 AM com.twitter.finagle.BaseResolver$$anonfun$resolvers$1 apply
INFO: Resolver[fixedinet] = com.twitter.finagle.FixedInetResolver(com.twitter.finagle.FixedInetResolver@1d2e91f5)
May 08, 2016 10:27:41 AM com.twitter.finagle.BaseResolver$$anonfun$resolvers$1 apply
INFO: Resolver[neg] = com.twitter.finagle.NegResolver$(com.twitter.finagle.NegResolver$@5c707aca)
May 08, 2016 10:27:41 AM com.twitter.finagle.BaseResolver$$anonfun$resolvers$1 apply
INFO: Resolver[nil] = com.twitter.finagle.NilResolver$(com.twitter.finagle.NilResolver$@5c8d932f)
May 08, 2016 10:27:41 AM com.twitter.finagle.BaseResolver$$anonfun$resolvers$1 apply
INFO: Resolver[fail] = com.twitter.finagle.FailResolver$(com.twitter.finagle.FailResolver$@52ba2221)
May 08, 2016 10:27:41 AM com.twitter.finagle.Init$$anonfun$1 apply$mcV$sp
[dlog] > test-proxy-writer
[dlog] >


// Output of `TailReader`
Opening log stream basic-stream-9
Log stream basic-stream-9 is empty.
Wait for records starting from DLSN{logSegmentSequenceNo=1, entryId=0, slotId=0}
Received record DLSN{logSegmentSequenceNo=1, entryId=0, slotId=0}
"""
test-proxy-writer
"""