This tutorial covers running Nutch jobs on Apache Tez (instead of MapReduce).
This tutorial is a work in progress and the document should be considered in DRAFT status. The work to evaluate Tez as an appropriate execution engine for Nutch jobs was initiated in December, 2020.
This tutorial will appeal to Nutch administrators looking to improve runtime speed whilst maintaining MapReduce’s ability to scale to petabytes of data. Readers are encouraged to share their experienced using Nutch on Tez.
Apache Tez is described as an application framework which allows for a complex directed-acyclic-graph (DAG) of tasks for processing data. It is currently built atop Apache Hadoop YARN.
The 2 main design themes for Tez are:
Empowering end users by:
Expressive dataflow definition APIs
Flexible Input-Processor-Output runtime model
Data type agnostic
Simplifying deployment
Execution Performance
Performance gains over Map Reduce
Optimal resource management
Plan reconfiguration at runtime
Dynamic physical data flow decisions
By allowing projects like Apache Hive and Apache Pig to run a complex DAG of tasks, Tez can be used to process data, that earlier took multiple MR jobs, now in a single Tez job as shown below.
Configuring and Deploying Hadoop Services
Hadoop was configured and deployed in pseudo-distributed mode. The following assumes that you have already established a pseudo-distributed cluster and will make the following configuration changes before launching the new cluster.
yarn-site.xmlExpand source
<configuration>
<!-- Site specific YARN configuration properties -->
<property>
<name>yarn.nodemanager.aux-services</name>
<value>mapreduce_shuffle</value>
</property>
<property>
<name>yarn.nodemanager.env-whitelist</name>
<value>JAVA_HOME,HADOOP_COMMON_HOME,HADOOP_HDFS_HOME,HADOOP_CONF_DIR,CLASSPATH_PREPEND_DISTCACHE,HADOOP_YARN_HOME,HADOOP_MAPRED_HOME</value>
</property>
<property>
<name>yarn.nodemanager.resource.memory-mb</name>
<value>8000</value>
<description>Amount of physical memory, in MB, that can be allocated for containers.</description>
</property>
<property>
<name>yarn.scheduler.minimum-allocation-mb</name>
<value>500</value>
</property>
<property>
<description>Indicate to clients whether Timeline service is enabled or not.
If enabled, the TimelineClient library used by end-users will post entities
and events to the Timeline server.</description>
<name>yarn.timeline-service.enabled</name>
<value>true</value>
</property>
<property>
<description>The hostname of the Timeline service web application.</description>
<name>yarn.timeline-service.hostname</name>
<value>localhost</value>
</property>
<property>
<description>Value must be the IP:PORT on which timeline server is running.</description>
<name>yarn.timeline-service.webapp.address</name>
<value>localhost:8188</value>
</property>
<property>
<description>Enables cross-origin support (CORS) for web services where
cross-origin web response headers are needed. For example, javascript making
a web services request to the timeline server.</description>
<name>yarn.timeline-service.http-cross-origin.enabled</name>
<value>true</value>
</property>
<property>
<description>Publish YARN information to Timeline Server</description>
<name> yarn.resourcemanager.system-metrics-publisher.enabled</name>
<value>true</value>
</property>
</configuration>
<configuration>
<property>
<name>tez.lib.uris</name>
<value>${fs.defaultFS}/apps/tez-0.10.1-SNAPSHOT/tez-0.10.1-SNAPSHOT.tar.gz#tez,${fs.defaultFS}/apps/nutch/apache-nutch-1.18-SNAPSHOT-bin.tar.gz#nutch</value>
</property>
<property>
<name>tez.lib.uris.classpath</name>
<value>./tez/tez-0.10.1-SNAPSHOT/*:./tez/tez-0.10.1-SNAPSHOT/lib/*:./nutch/apache-nutch-1.18-SNAPSHOT/*:./nutch/apache-nutch-1.18-SNAPSHOT/conf/*:./nutch/apache-nutch-1.18-SNAPSHOT/lib/*:./nutch/apache-nutch-1.18-SNAPSHOT/plugins/*/*</value>
</property>
<property>
<name>tez.use.cluster.hadoop-libs</name>
<value>true</value>
</property>
<property>
<name>plugin.folders</name>
<value>nutch/apache-nutch-1.18-SNAPSHOT/plugins</value>
</property>
<property>
<description>Enable Tez to use the Timeline Server for History Logging</description>
<name>tez.history.logging.service.class</name>
<value>org.apache.tez.dag.history.logging.ats.ATSHistoryLoggingService</value>
</property>
<property>
<description>URL for where the Tez UI is hosted</description>
<name>tez.tez-ui.history-url.base</name>
<value>http://localhost:8080/tez-ui-0.10.1-SNAPSHOT</value>
</property>
<property>
<name>tez.runtime.convert.user-payload.to.history-text</name>
<value>true</value>
</property>
</configuration>
Deploy tez web application to TomcatExpand source
//assuming that Apache Tomcat is installed and running
cp $TEZ_HOME/tez-ui/target/tez-ui-0.10.1-SNAPSHOT.war $TOMCAT_HOME/webapps
Configuring and Deploying Nutch
Build Nutch and Copy to HDFSExpand source
cd $NUTCH_HOME && ant clean tar-bin
hadoop fs -copyFromLocal dist/apache-nutch-1.18-SNAPSHOT-bin.tar.gz /apps/nutch-1.18-SNAPSHOT
You can then run Nutch jobs as usual e.g. nutch inject crawldb urls. Once the job is submitted to YARN you can use the the tez-ui application deployed into Tomcat (should be at http://localhost:8080/tez-ui-0.10.1-SNAPSHOT/) to view Tez jobs. The screenshots below show some examples
Evaluating Tez as a Replacement for MapReduce
The following content relates to ongoing experiments which have been run by members of the Nutch community.
Experiments
Running the Injector job on Tez
Run #
YARN Engine
# of URLs
Elapsed Time
1
MapReduce
11523
00:00:34
2
MapReduce
11523
00:00:32
3
MapReduce
11523
00:00:34
4
Tez
11523
00:00:42
5
Tez
11523
00:00:13
6
Tez
11523
00:00:14
7
MapReduce
15763469
00:03:21
8
MapReduce
15763469
00:03:13
9
MapReduce
15763469
00:02:38
10
MapReduce
15763469
00:02:37
11
MapReduce
15763469
00:02:48
12
Tez
15763469
00:02:14
13
Tez
15763469
00:02:10
14
Tez
15763469
00:02:13
Both Tez and MapReduce appear to eventually gain performance improvements after a few runs. For shorter tasks we already find a performance improvement because of the default tez.am.container.reuse.enabled=true configuration property. This especially applies for shorter runtimes, where e.g. JVM startup time/warmup really counts. The above runtimes represent a cold -> warm pattern. Clearly after warm up, Tez appears to offer significant runtime improvements over MapReduce. This is very promising however much more experimentation is required.
Running the Generator job on Tez
Run #
YARN Engine
# of URLS
Elapsed Time
1
MapReduce
11322
00:01:19
2
MapReduce
11322
00:01:18
3
MapReduce
11322
00:01:22
4
MapReduce
11322
00:01:23
5
Tez
N/A
N/A
6
Tez
N/A
N/A
7
Tez
N/A
N/A
8
Tez
N/A
N/A
As of it was discovered that the Generator job is incompatible with Tez. The job execution log below details the outcome.
Generator job incompatible with TezExpand source
$ nutch generate crawldb segments5
...
2020-12-22 10:17:05,168 WARN util.NativeCodeLoader: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable
2020-12-22 10:17:05,759 INFO crawl.Generator: Generator: starting at 2020-12-22 10:17:05
2020-12-22 10:17:05,759 INFO crawl.Generator: Generator: Selecting best-scoring urls due for fetch.
2020-12-22 10:17:05,759 INFO crawl.Generator: Generator: filtering: true
2020-12-22 10:17:05,759 INFO crawl.Generator: Generator: normalizing: true
2020-12-22 10:17:05,955 INFO client.RMProxy: Connecting to ResourceManager at /0.0.0.0:8032
2020-12-22 10:17:06,071 INFO client.AHSProxy: Connecting to Application History server at localhost/127.0.0.1:10200
2020-12-22 10:17:06,308 INFO mapreduce.JobResourceUploader: Disabling Erasure Coding for path: /tmp/hadoop-yarn/staging/lmcgibbn/.staging/job_1608661005352_0001
2020-12-22 10:17:07,115 INFO input.FileInputFormat: Total input files to process : 1
2020-12-22 10:17:07,161 INFO mapreduce.JobSubmitter: number of splits:1
2020-12-22 10:17:07,387 INFO mapreduce.JobSubmitter: Submitting tokens for job: job_1608661005352_0001
2020-12-22 10:17:07,388 INFO mapreduce.JobSubmitter: Executing with tokens: []
2020-12-22 10:17:07,531 INFO client.YARNRunner: Number of stages: 2
2020-12-22 10:17:07,597 INFO conf.Configuration: resource-types.xml not found
2020-12-22 10:17:07,598 INFO resource.ResourceUtils: Unable to find 'resource-types.xml'.
2020-12-22 10:17:07,809 INFO counters.Limits: Counter limits initialized with parameters: GROUP_NAME_MAX=256, MAX_GROUPS=500, COUNTER_NAME_MAX=64, MAX_COUNTERS=1200
2020-12-22 10:17:07,809 INFO counters.Limits: Counter limits initialized with parameters: GROUP_NAME_MAX=256, MAX_GROUPS=500, COUNTER_NAME_MAX=64, MAX_COUNTERS=120
2020-12-22 10:17:07,809 INFO client.TezClient: Tez Client Version: [ component=tez-api, version=0.10.1-SNAPSHOT, revision=849e1d7694cdfd2432d631830940bc95c6f26ead, SCM-URL=scm:git:https://gitbox.apache.org/repos/asf/tez.git, buildTime=2020-12-17T01:41:13Z, buildUser=lmcgibbn, buildJavaVersion=1.8.0_221 ]
2020-12-22 10:17:07,825 INFO client.RMProxy: Connecting to ResourceManager at /0.0.0.0:8032
2020-12-22 10:17:07,825 INFO client.AHSProxy: Connecting to Application History server at localhost/127.0.0.1:10200
2020-12-22 10:17:07,826 INFO client.TezClient: Submitting DAG application with id: application_1608661005352_0001
2020-12-22 10:17:07,828 INFO client.TezClientUtils: Using tez.lib.uris value from configuration: hdfs://localhost:9000/apps/tez-0.10.1-SNAPSHOT/tez-0.10.1-SNAPSHOT.tar.gz#tez,hdfs://localhost:9000/apps/nutch/apache-nutch-1.18-SNAPSHOT-bin.tar.gz#nutch
2020-12-22 10:17:07,828 INFO client.TezClientUtils: Using tez.lib.uris.classpath value from configuration: ./tez/tez-0.10.1-SNAPSHOT/*:./tez/tez-0.10.1-SNAPSHOT/lib/*:./nutch/apache-nutch-1.18-SNAPSHOT/*:./nutch/apache-nutch-1.18-SNAPSHOT/conf/*:./nutch/apache-nutch-1.18-SNAPSHOT/lib/*:./nutch/apache-nutch-1.18-SNAPSHOT/plugins/*/*
2020-12-22 10:17:07,842 INFO client.TezClient: Tez system stage directory hdfs://localhost:9000/tmp/hadoop-yarn/staging/lmcgibbn/.staging/job_1608661005352_0001/.tez/application_1608661005352_0001 doesn't exist and is created
2020-12-22 10:17:08,413 INFO client.TezClient: Submitting DAG to YARN, applicationId=application_1608661005352_0001, dagName=generate: select from crawldb
2020-12-22 10:17:08,787 INFO impl.YarnClientImpl: Submitted application application_1608661005352_0001
2020-12-22 10:17:08,790 INFO client.TezClient: The url to track the Tez AM: http://localhost:8088/proxy/application_1608661005352_0001/
^[[C2020-12-22 10:17:50,693 INFO client.RMProxy: Connecting to ResourceManager at /0.0.0.0:8032
2020-12-22 10:17:50,693 INFO client.AHSProxy: Connecting to Application History server at localhost/127.0.0.1:10200
2020-12-22 10:17:50,720 INFO mapreduce.Job: The url to track the job: http://localhost:8088/proxy/application_1608661005352_0001/
2020-12-22 10:17:50,721 INFO mapreduce.Job: Running job: job_1608661005352_0001
2020-12-22 10:17:51,729 INFO mapreduce.Job: Job job_1608661005352_0001 running in uber mode : false
2020-12-22 10:17:51,731 INFO mapreduce.Job: map 0% reduce 0%
2020-12-22 10:17:56,764 INFO mapreduce.Job: map 100% reduce 0%
2020-12-22 10:17:56,766 INFO mapreduce.Job: map 100% reduce 100%
2020-12-22 10:17:56,768 INFO mapreduce.Job: Job job_1608661005352_0001 completed successfully
2020-12-22 10:17:56,775 INFO mapreduce.Job: Counters: 0
2020-12-22 10:17:56,776 INFO crawl.Generator: Generator: number of items rejected during selection:
2020-12-22 10:17:56,806 WARN crawl.Generator: Generator: 0 records selected for fetching, exiting ...
Observed Issues
When using Tez, counters are not populated. This makes sense as all existing counters are created using MapReduce framework Context objects. This presents a major issue. Counters are a requirement to have as they are key to regular inspections of ongoing crawls, finding errors and debugging. The org.apache.tez.common.counters package may offer a equivalent replacement but this has still to be investigated.
As of it was discovered that the Generator job is incompatible with Tez. Again there are no counters so this could be the expected behaviour.
