Cloudera HBase Certification Questions and Answers (Dumps and Practice Questions)

Question : You have data already stored in HDFS and are considering using HBase. Which additional feature does HBase provide to HDFS ?

1. Random Writes
2. Batch Processing
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4. Scalablity

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Answer with explanation:

HBase adds random read/write access to HDFS

Hadoop is scalable but..
* MapReduce slow and difficult
* Does not support random writes
* Poor support for random reads

Question :

Your client application calls the following method for all puts to the single table notiifcations put.setWriteToWAL(false);
One region, region1 for the notifications table is assigned to RegionServer rs1. Which of the following statements describes the result of
RegionServer rs1 crashing ?

1. All data in the notifications table is lost
2. No data is lost
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4. Data for your client application in the MemStores for region1 is lost.

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Explanation: HBase uses write Ahead Log, if you dont write to it you will lose all the data thats only in the memstores when a region server fails.
This setting is useful for importing a lot of data.

Question :

Which of the following configuration values determines automated splitting ?

1. hbase.hregion.majorcompaction
2. hbase.hregion.flush.size
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4. hbase.hregion.max.filesize

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Answer with explanation:

Consider going to larger regions to cut down on the total number of regions on your cluster. Generally less
Regions to manage makes for a smoother running cluster (You can always latermanually split the big Regions
should one prove hot and you want to spread the request load over the cluster). A lower number of regions is
preferred, generally in the range of 20 to low- hundreds per RegionServer. Adjust the regionsize as
appropriate to achieve this number.

For the 0.90.x codebase, the upper-bound of regionsize is about 4Gb, with a default of 256Mb. For 0.92.x
codebase, due to the HFile v2 change much larger regionsizes can be supported (e.g., 20Gb).
You may need to experiment with this setting based on your hardware configuration and application needs.
Adjust hbase.hregion.max.filesize in your hbase-site.xml. RegionSize can also be set on a per- table basis via
HTableDescriptor.

Related Questions

Question :

You want to do mostly full table scans on your data. In order to improve performance you increase your block
size. Why does this improve your scan performance?

1. It does not. Increasing block size does not improve scan performance.
2. It does not. Increasing block size means that fewer blocks fit into your block cache. This requires HBase to
read each block from disk rather than cache for each scan, thereby decreasing scan performance.
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4. Increasing block size means fewer block indexes that need to be read from disk, thereby increasing scan performance.

Question :

Your client application connects to HBase for the first time and queries the .META. table. What information
does the .META. table provide to your client application?

1. The location of a Region
2. The location of an MMaster
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4. The location of a ROOT table

Question :

You have a table where keys range from "A" to "Z", and you want to scan from "D" to "H." Which of the
following is true?

1. A MultiGet must be issued for rows D, E, F, G, H.
2. The scan class supports ranges via the stop and start rows.
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4. In order to range scan, raw scan mode must be enabled.

Question :

Your client connects to HBase for the first time to read a row user_1234 located in a table Users. What
process does your client use to find the correct RegionServer to which it should send the request?

1. The client looks up the location of ROOT, in which it looks up the location of META, in which it looks up the
location of the correct Users region.
2. The client looks up the location of the master, in which it looks up the location of META, in which it looks up
the location of the correct Users region.
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4. The client queries the master to find the location of the Users table.

Question :

Your data load application is maintaining a custom versioning scheme (not using the timestamp as the version
number). You accidentally executed three writes to a given cell all with the same version during which time no
flushes have occurred. Which of the three data writes will dBase maintain?

1. None of the writes to cell
2. The last write to cell
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4. All of the writes to cell

Question :

Your client application needs to write a row to a region that has, recently split. Where will the row be written?

1. One of the daughter regions
2. The original region
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4. The HMaster