HDFS-8284. Update documentation about how to use HTrace with HDFS (Masatake Iwasaki via Colin P. McCabe)
This commit is contained in:
Colin Patrick Mccabe
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730f9930a4
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8f7c2364d7
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@ -1756,18 +1756,6 @@ for ldap providers in the same way as above does.
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</description>
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</property>
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<property>
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<name>hadoop.htrace.spanreceiver.classes</name>
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<value></value>
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<description>
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A comma separated list of the fully-qualified class name of classes
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implementing SpanReceiver. The tracing system works by collecting
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information in structs called 'Spans'. It is up to you to choose
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how you want to receive this information by implementing the
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SpanReceiver interface.
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</description>
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</property>
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<property>
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<name>ipc.server.max.connections</name>
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<value>0</value>
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@ -18,13 +18,13 @@ Enabling Dapper-like Tracing in Hadoop
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* [Enabling Dapper-like Tracing in Hadoop](#Enabling_Dapper-like_Tracing_in_Hadoop)
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* [Dapper-like Tracing in Hadoop](#Dapper-like_Tracing_in_Hadoop)
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* [HTrace](#HTrace)
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* [Samplers](#Samplers)
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* [SpanReceivers](#SpanReceivers)
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* [Setting up ZipkinSpanReceiver](#Setting_up_ZipkinSpanReceiver)
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* [Dynamic update of tracing configuration](#Dynamic_update_of_tracing_configuration)
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* [Starting tracing spans by HTrace API](#Starting_tracing_spans_by_HTrace_API)
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* [Sample code for tracing](#Sample_code_for_tracing)
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* [Starting tracing spans by configuration for HDFS client](#Starting_tracing_spans_by_configuration_for_HDFS_client)
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Dapper-like Tracing in Hadoop
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-----------------------------
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@ -32,83 +32,51 @@ Dapper-like Tracing in Hadoop
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[HDFS-5274](https://issues.apache.org/jira/browse/HDFS-5274) added support for tracing requests through HDFS,
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using the open source tracing library,
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[Apache HTrace](https://git-wip-us.apache.org/repos/asf/incubator-htrace.git).
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[Apache HTrace](http://htrace.incubator.apache.org/).
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Setting up tracing is quite simple, however it requires some very minor changes to your client code.
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### Samplers
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Configure the samplers in `core-site.xml` property: `hadoop.htrace.sampler`.
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The value can be NeverSampler, AlwaysSampler or ProbabilitySampler.
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NeverSampler: HTrace is OFF for all spans;
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AlwaysSampler: HTrace is ON for all spans;
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ProbabilitySampler: HTrace is ON for some percentage% of top-level spans.
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<property>
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<name>hadoop.htrace.sampler</name>
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<value>NeverSampler</value>
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</property>
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### SpanReceivers
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The tracing system works by collecting information in structs called 'Spans'.
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It is up to you to choose how you want to receive this information
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by implementing the SpanReceiver interface, which defines one method:
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by using implementation of [SpanReceiver](http://htrace.incubator.apache.org/#Span_Receivers)
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interface bundled with HTrace or implementing it by yourself.
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public void receiveSpan(Span span);
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[HTrace](http://htrace.incubator.apache.org/) provides options such as
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Configure what SpanReceivers you'd like to use
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* FlumeSpanReceiver
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* HBaseSpanReceiver
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* HTracedRESTReceiver
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* ZipkinSpanReceiver
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In order to set up SpanReceivers for HDFS servers,
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configure what SpanReceivers you'd like to use
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by putting a comma separated list of the fully-qualified class name of classes implementing SpanReceiver
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in `core-site.xml` property: `hadoop.htrace.spanreceiver.classes`.
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in `hdfs-site.xml` property: `dfs.htrace.spanreceiver.classes`.
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```xml
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<property>
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<name>hadoop.htrace.spanreceiver.classes</name>
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<name>dfs.htrace.spanreceiver.classes</name>
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<value>org.apache.htrace.impl.LocalFileSpanReceiver</value>
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</property>
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<property>
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<name>hadoop.htrace.local-file-span-receiver.path</name>
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<name>dfs.htrace.local-file-span-receiver.path</name>
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<value>/var/log/hadoop/htrace.out</value>
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</property>
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```
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You can omit package name prefix if you use span receiver bundled with HTrace.
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```xml
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<property>
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<name>hadoop.htrace.spanreceiver.classes</name>
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<name>dfs.htrace.spanreceiver.classes</name>
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<value>LocalFileSpanReceiver</value>
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</property>
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```
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### Setting up ZipkinSpanReceiver
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Instead of implementing SpanReceiver by yourself,
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you can use `ZipkinSpanReceiver` which uses
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[Zipkin](https://github.com/twitter/zipkin) for collecting and displaying tracing data.
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In order to use `ZipkinSpanReceiver`,
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you need to download and setup [Zipkin](https://github.com/twitter/zipkin) first.
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you also need to add the jar of `htrace-zipkin` to the classpath of Hadoop on each node.
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Here is example setup procedure.
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$ git clone https://github.com/cloudera/htrace
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$ cd htrace/htrace-zipkin
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$ mvn compile assembly:single
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$ cp target/htrace-zipkin-*-jar-with-dependencies.jar $HADOOP_HOME/share/hadoop/common/lib/
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The sample configuration for `ZipkinSpanReceiver` is shown below.
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By adding these to `core-site.xml` of NameNode and DataNodes, `ZipkinSpanReceiver` is initialized on the startup.
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You also need this configuration on the client node in addition to the servers.
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<property>
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<name>hadoop.htrace.spanreceiver.classes</name>
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<value>ZipkinSpanReceiver</value>
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</property>
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<property>
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<name>hadoop.htrace.zipkin.collector-hostname</name>
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<value>192.168.1.2</value>
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</property>
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<property>
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<name>hadoop.htrace.zipkin.collector-port</name>
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<value>9410</value>
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</property>
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You also need to add the jar bundling SpanReceiver to the classpath of Hadoop
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on each node. (LocalFileSpanReceiver in the example above is included in the
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jar of htrace-core which is bundled with Hadoop.)
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### Dynamic update of tracing configuration
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@ -136,8 +104,8 @@ You need to run the command against all servers if you want to update the config
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You need to specify the class name of span receiver as argument of `-class` option.
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You can specify the configuration associated with span receiver by `-Ckey=value` options.
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$ hadoop trace -add -class LocalFileSpanReceiver -Chadoop.htrace.local-file-span-receiver.path=/tmp/htrace.out -host 192.168.56.2:9000
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Added trace span receiver 2 with configuration hadoop.htrace.local-file-span-receiver.path = /tmp/htrace.out
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$ hadoop trace -add -class LocalFileSpanReceiver -Cdfs.htrace.local-file-span-receiver.path=/tmp/htrace.out -host 192.168.56.2:9000
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Added trace span receiver 2 with configuration dfs.htrace.local-file-span-receiver.path = /tmp/htrace.out
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$ hadoop trace -list -host 192.168.56.2:9000
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ID CLASS
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@ -149,8 +117,9 @@ In order to trace, you will need to wrap the traced logic with **tracing span**
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When there is running tracing spans,
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the tracing information is propagated to servers along with RPC requests.
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In addition, you need to initialize `SpanReceiver` once per process.
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In addition, you need to initialize `SpanReceiverHost` once per process.
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```java
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import org.apache.hadoop.hdfs.HdfsConfiguration;
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import org.apache.hadoop.tracing.SpanReceiverHost;
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import org.apache.htrace.Sampler;
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@ -169,14 +138,17 @@ In addition, you need to initialize `SpanReceiver` once per process.
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} finally {
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if (ts != null) ts.close();
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}
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```
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### Sample code for tracing
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### Sample code for tracing by HTrace API
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The `TracingFsShell.java` shown below is the wrapper of FsShell
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which start tracing span before invoking HDFS shell command.
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```java
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import org.apache.hadoop.conf.Configuration;
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import org.apache.hadoop.fs.FsShell;
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import org.apache.hadoop.hdfs.DFSConfigKeys;
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import org.apache.hadoop.tracing.SpanReceiverHost;
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import org.apache.hadoop.util.ToolRunner;
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import org.apache.htrace.Sampler;
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@ -189,7 +161,7 @@ which start tracing span before invoking HDFS shell command.
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FsShell shell = new FsShell();
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conf.setQuietMode(false);
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shell.setConf(conf);
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SpanReceiverHost.getInstance(conf);
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SpanReceiverHost.get(conf, DFSConfigKeys.DFS_SERVER_HTRACE_PREFIX);
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int res = 0;
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TraceScope ts = null;
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try {
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@ -202,8 +174,40 @@ which start tracing span before invoking HDFS shell command.
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System.exit(res);
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}
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}
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```
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You can compile and execute this code as shown below.
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$ javac -cp `hadoop classpath` TracingFsShell.java
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$ java -cp .:`hadoop classpath` TracingFsShell -ls /
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### Starting tracing spans by configuration for HDFS client
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The DFSClient can enable tracing internally. This allows you to use HTrace with
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your client without modifying the client source code.
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Configure the span receivers and samplers in `hdfs-site.xml`
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by properties `dfs.client.htrace.sampler` and `dfs.client.htrace.sampler`.
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The value of `dfs.client.htrace.sampler` can be NeverSampler, AlwaysSampler or ProbabilitySampler.
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* NeverSampler: HTrace is OFF for all requests to namenodes and datanodes;
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* AlwaysSampler: HTrace is ON for all requests to namenodes and datanodes;
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* ProbabilitySampler: HTrace is ON for some percentage% of requests to namenodes and datanodes
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You do not need to enable this if your client program has been modified
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to use HTrace.
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```xml
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<property>
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<name>dfs.client.htrace.spanreceiver.classes</name>
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<value>LocalFileSpanReceiver</value>
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</property>
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<property>
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<name>dfs.client.htrace.sampler</name>
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<value>ProbabilitySampler</value>
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</property>
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<property>
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<name>dfs.client.htrace.sampler.fraction</name>
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<value>0.5</value>
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</property>
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```
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@ -527,6 +527,9 @@ Release 2.8.0 - UNRELEASED
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HDFS-5640. Add snapshot methods to FileContext. (Rakesh R via cnauroth)
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HDFS-8284. Update documentation about how to use HTrace with HDFS (Masatake
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Iwasaki via Colin P. McCabe)
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OPTIMIZATIONS
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HDFS-8026. Trace FSOutputSummer#writeChecksumChunks rather than
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@ -2316,4 +2316,22 @@
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the delay time will increase exponentially(double) for each retry.
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</description>
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</property>
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<property>
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<name>dfs.htrace.spanreceiver.classes</name>
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<value></value>
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<description>
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The class name of the HTrace SpanReceiver for the NameNode and DataNode.
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</description>
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</property>
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<property>
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<name>dfs.client.htrace.spanreceiver.classes</name>
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<value></value>
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<description>
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The class name of the HTrace SpanReceiver for the HDFS client. You do not
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need to enable this if your client program has been modified to use HTrace.
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</description>
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</property>
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</configuration>
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