Re: MapReduce reindexing with authentication


Boxuan Li
 

Hi Marc,

That is an interesting solution. I was not aware of the mapreduce.application.classpath property. It is not well documented, but from what I understand, this option is used primarily to distribute the mapreduce framework rather than user files. Glad to know it can be used for user files as well.
I am not 100% sure, but seems it requires you to upload the file to hdfs first (if you are using a yarn cluster). The ToolRunner, however, can add a file from local filesystem too. We prefer not to store keytab files on hdfs permanently. This difference is subtle, though. Also, we don’t use gremlin console anyway, so not being able to do so via gremlin console is not a drawback for us.

Agree with you that the documentation can be enhanced. Right now it simply says “The class starts a Hadoop MapReduce job using the Hadoop configuration and jars on the classpath.”, which is too brief and assumes users have a good knowledge of Hadoop MapReduce.

> One could even think of putting the mapreduce properties in the graph properties file and pass on properties of this namespace to the mapreduce client.

Not sure if it’s possible, but if someone implements it, it would be very helpful for users to do quick start without worrying about the cumbersome Hadoop configs.

Best regards,
Boxuan

「<hadoopmarc@...>」在 2021年5月24日 週一,下午3:48 寫道:

Hi Boxuan,

Yes, you are right, I mixed things up by wrongly interpreting GENERIC_OPTIONS as an env variable. I did some additional experiments. though, bringing in new information.

1. It is possible to put a mapred-site.xml file on the JanusGraph classpath that is automatically loaded by the mapreduce client. When using the file below during mapreduce reindexing, I get the following exception (on purpose):

gremlin> mr.updateIndex(i, SchemaAction.REINDEX).get()
java.io.FileNotFoundException: File file:/tera/lib/janusgraph-full-0.5.3/hi.tgz does not exist

The mapreduce config parameters are listed in https://hadoop.apache.org/docs/r2.7.3/hadoop-mapreduce-client/hadoop-mapreduce-client-core/mapred-default.xml
The description for mapreduce.application.framework.path suggests that you can pass additional files to the mapreduce workers using this option (without any changes to JanusGraph).

<?xml version="1.0" encoding="UTF-8"?>
<?xml-stylesheet type="text/xsl" href="configuration.xsl"?>
<configuration>
  <property>
    <name>mapreduce.framework.name</name>
    <value>local</value>
  </property>
  <property>
    <name>mapreduce.application.classpath</name>
    <value>dummy</value>
  </property>
  <property>
    <name>mapreduce.application.framework.path</name>
    <value>hi.tgz</value>
  </property>
  <property>
    <name>mapred.map.tasks</name>
    <value>2</value>
  </property>
  <property>
    <name>mapred.reduce.tasks</name>
    <value>2</value>
  </property>
</configuration>

2. When using mapreduce reindexing in the documented way, it already issues the following warning:
08:49:55 WARN  org.apache.hadoop.mapreduce.JobResourceUploader  - Hadoop command-line option parsing not performed. Implement the Tool interface and execute your application with ToolRunner to remedy this.

When you would resolve your keytab issue by modifying the JanusGraph code and calling the hadoop ToolRunner, you have the additional advantage of getting rid of this warning. This would not work from the gremlin console, though, unless gremlin.sh passes the additional command line options to the java command line (ugly).

So, I think I would prefer the option with mapred-site.xml. It would not hurt to slightly extend the mapreduce reindexing documentation, anyway:
  • when calling from the gremlin console, you need an "import org.janusgraph.hadoop.MapReduceIndexManagement"
  • mapreduce has a default setting mapreduce.framework.name=local. Where do you set mapreduce.framework.name=yarn for using your cluster? One could even think of putting the mapreduce properties in the graph properties file and pass on properties of this namespace to the mapreduce client.
Best wishes,    Marc

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