DistributedLog

git@github.com:twitter/distributedlog.git/tree/master/
OWNERS None
TAGS #uses_maven
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Write Records using Core Library

This tutorial shows how to write records using core library.

Open a writer

  • Create distributedlog URI.

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

  • Create distributedlog configuration.

    DistributedLogConfiguration conf = new DistributedLogConfiguration();

  • Enable immediate flush.

    conf.setImmediateFlushEnabled(true);
conf.setOutputBufferSize(0);
conf.setPeriodicFlushFrequencyMilliSeconds(0);

  • Enable immediate locking. So if there is already a writer wring to the stream, opening another writer will fail because previous writer already held a lock.

    conf.setLockTimeout(DistributedLogConstants.LOCK_IMMEDIATE);

  • Build the distributedlog namespace.

    DistributedLogNamespace namespace = DistributedLogNamespaceBuilder.newBuilder()
        .conf(conf)
        .uri(uri)
        .regionId(DistributedLogConstants.LOCAL_REGION_ID)
        .clientId("console-writer")
        .build();

  • Open the writer.

    DistributedLogManager dlm = namespace.openLog("basic-stream-1");
AsyncLogWriter writer = FutureUtils.result(dlm.openAsyncLogWriter());

Write Records

  • Construct a log record using System.currentTimeMillis() as the TransactionID.

    byte[] data = ...;
LogRecord record = new LogRecord(System.currentTimeMillis(), data);

  • Write the log record.

    Future<DLSN> writeFuture = writer.write(record);

  • Register a future listener on write completion.

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

    @Override
    public void onSuccess(DLSN value) {
        // executed when write completed.
    }
});

Close the writer

  • Close the writer after usage.

    FutureUtils.result(writer.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. Create the stream under the distributedlog uri.

    // Create Stream `basic-stream-1`
// 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 1

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

    // Tailing Stream `basic-stream-1`
// 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-1

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

    // Write Records into Stream `basic-stream-1`
// runner run com.twitter.distributedlog.basic.ConsoleWriter ${distributedlog-uri} ${stream}
./distributedlog-tutorials/distributedlog-basic/bin/runner run com.twitter.distributedlog.basic.ConsoleWriter distributedlog://127.0.0.1:7000/messaging/distributedlog basic-stream-1

  5. Example output from ConsoleWriter and TailReader.

    // Output of `ConsoleWriter`
Opening log stream basic-stream-1
[dlog] > test!
[dlog] >


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

  6. Open another terminal to run ConsoleWriter. It would fail with OwnershipAcquireFailedException as previous ConsoleWriter is still holding lock on writing to stream basic-stream-1.

    Opening log stream basic-stream-1
Exception in thread "main" com.twitter.distributedlog.exceptions.OwnershipAcquireFailedException: LockPath - /messaging/distributedlog/basic-stream-1/<default>/lock: Lock acquisition failed, the current owner is console-writer
    at com.twitter.distributedlog.lock.ZKSessionLock$8.apply(ZKSessionLock.java:570)
    at com.twitter.distributedlog.lock.ZKSessionLock$8.apply(ZKSessionLock.java:567)
    at com.twitter.util.Future$$anonfun$map$1$$anonfun$apply$8.apply(Future.scala:1041)
    at com.twitter.util.Try$.apply(Try.scala:13)
    at com.twitter.util.Future$.apply(Future.scala:132)
    at com.twitter.util.Future$$anonfun$map$1.apply(Future.scala:1041)
    at com.twitter.util.Future$$anonfun$map$1.apply(Future.scala:1040)
    at com.twitter.util.Promise$Transformer.liftedTree1$1(Promise.scala:112)
    at com.twitter.util.Promise$Transformer.k(Promise.scala:112)
    at com.twitter.util.Promise$Transformer.apply(Promise.scala:122)
    at com.twitter.util.Promise$Transformer.apply(Promise.scala:103)
    at com.twitter.util.Promise$$anon$1.run(Promise.scala:357)
    at com.twitter.concurrent.LocalScheduler$Activation.run(Scheduler.scala:178)
    at com.twitter.concurrent.LocalScheduler$Activation.submit(Scheduler.scala:136)
    at com.twitter.concurrent.LocalScheduler.submit(Scheduler.scala:207)
    at com.twitter.concurrent.Scheduler$.submit(Scheduler.scala:92)
    at com.twitter.util.Promise.runq(Promise.scala:350)
    at com.twitter.util.Promise.updateIfEmpty(Promise.scala:716)
    at com.twitter.util.Promise.update(Promise.scala:694)
    at com.twitter.util.Promise.setValue(Promise.scala:670)
    at com.twitter.distributedlog.lock.ZKSessionLock$9.safeRun(ZKSessionLock.java:622)
    at org.apache.bookkeeper.util.SafeRunnable.run(SafeRunnable.java:31)
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
    at java.util.concurrent.FutureTask.run(FutureTask.java:262)
    at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:178)
    at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:292)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at java.lang.Thread.run(Thread.java:745)