45 Frequently asked questions about Hadoop

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1.3 Modes A Hadoop cluster can run

• Stand-alone (local) mode
• Pseudo-distributed mode
• Fully distributed mode

2. note points in stand-alone (local) mode?

There is no daemon in stand-alone mode (standalone), and everything runs on a JVM. There is also no DFS here, using the local file system. Stand-alone mode is suitable for running mapreduce programs during development, which is also the least used mode.

3. What are the points of note in pseudo-distribution mode?

Pseudo-distributed (Pseudo) is suitable for development and test environments where all daemons run on the same machine.

4. can VMS be called pseudo?

No, two things, and pseudo only for Hadoop.

5. What are the points of attention in the full distribution model?

The full distribution pattern is typically used in production environments where we use n hosts to form a Hadoop cluster, with the Hadoop daemon running on top of each host. There will be Namenode running hosts, Datanode running hosts, and task tracker running hosts. In a distributed environment, the master and slave nodes are separated.

6. does Hadoop follow Unix mode?

Yes, Hadoop also has a "conf" directory under UNIX use cases.

7. What directory is Hadoop installed in?

Cloudera and Apache use the same directory structure, and Hadoop is installed in cd/usr/lib/hadoop-0.20/.

8. What is the port number for Namenode, Job Tracker, and task tracker?

Namenode,70;job Tracker,30;task tracker,60.

9. What is the core configuration of Hadoop?

The core configuration of Hadoop is done through two XML files: 1,hadoop-default.xml;2,hadoop-site.xml. These files are in XML format, so there are attributes in each XML, including names and values, but these files are no longer present.

How do I configure it now?

Hadoop now has 3 configuration files: 1,core-site.xml;2,hdfs-site.xml;3,mapred-site.xml. These files are saved in the conf/subdirectory.

What is the overflow factor for ram?

The overflow factor (spill factor) is the size of the file stored in the temporary file, which is the Hadoop-temp directory.

Fs.mapr.working.dir is just a single directory?

Fs.mapr.working.dir is just a directory.

3 main attributes of Hdfs-site.xml?

• Dfs.name.dir determines the path to the metadata store and how DFS is stored (disk or remote)
• Dfs.data.dir determines the path to the data store
• Fs.checkpoint.dir for the second Namenode

How do I exit input mode?

Exit the input by: 1, press esc;2, type: Q (If you do not enter any now) or type: Wq (if you have entered now), and press ENTER.

What happened to the system when you entered HADOOPFSCK/caused "Connection refused Java exception"?

45 Frequently asked questions about Hadoop