Madanswer Technologies Interview Questions Data|Agile|DevOPs|Python - Recent questions and answers in HBase

Answered: What is compaction in HBase?

Sat, 13 Jun 2020 09:08:38 +0000

As more and more data is written to Hbase, many HFiles get created. Compaction is the process of merging these HFiles to one file and after the merged file is created successfully, discard the old file.

Answered: What are the different compaction types in HBase?

Sat, 13 Jun 2020 09:08:23 +0000

There are two types of compaction. Major and Minor compaction. In minor compaction, the adjacent small HFiles are merged to create a single HFile without removing the deleted HFiles. Files to be merged are chosen randomly.

In Major compaction, all the HFiles of a column are emerged and a single HFiles is created. The delted HFiles are discarded and it is generally triggered manually.

Answered: What is the difference between the commands delete column and delete family in HBase?

Sat, 13 Jun 2020 09:08:02 +0000

The Delete column command deletes all versions of a column but the delete family deletes all columns of a particular family.

Answered: What is a cell in HBase?

Sat, 13 Jun 2020 09:07:38 +0000

A cell in Hbase is the smallest unit of a Hbase table which holds a piece of data in the form of a tuple{row,column,version}

Answered: What is the role of the class HColumnDescriptor in HBase?

Sat, 13 Jun 2020 09:07:10 +0000

This class is used to store information about a column family such as the number of versions, compression settings, etc. It is used as input when creating a table or adding a column.

Answered: What is the lower bound of versions in HBase?

Sat, 13 Jun 2020 09:06:44 +0000

The lower bound of versions indicates the minimum number of versions to be stored in Hbase for a column. For example If the value is set to 3 then three latest version wil be maintained and the older ones will be removed.

Answered: What is TTL (Time to live) in HBase?

Sat, 13 Jun 2020 09:06:22 +0000

TTL is a data retention technique using which the version of a cell can be preserved till a specific time period.Once that timestamp is reached the specific version will be removed.

Answered: Does Hbase support table joins in HBase?

Sat, 13 Jun 2020 09:05:56 +0000

Hbase does not support table jons. But using a mapreduce job we can specify join queries to retrieve data from multiple Hbase tables.

Answered: What is a rowkey in HBase?

Sat, 13 Jun 2020 09:05:13 +0000

Each row in Hbase is identified by a unique byte of array called row key.

Answered: What are the two ways in which you can access data from Hbase?

Sat, 13 Jun 2020 09:04:02 +0000

The data in Hbase can be accessed in two ways.

Using the rowkey and table scan for a range of row key values.

Using mapreduce in a batch manner.

Answered: What are the two types of table design approach in HBase?

Sat, 13 Jun 2020 09:03:50 +0000

They are - (i) Short and Wide (ii) Tall and Thin

Answered: In which scenario should we consider creating a short and wide Hbase table?

Sat, 13 Jun 2020 09:03:38 +0000

The short and wide table design is considered when there is

There is a small number of columns

There is a large number of rows

Answered: In Which scenario should we consider a Tall-thin table design in HBase?

Sat, 13 Jun 2020 09:03:22 +0000

The tall and thin table design is considered when there is

There is a large number of columns

There is a small number of rows

Answered: Give a command to store 4 versions in a table rather than the default 3.

Sat, 13 Jun 2020 09:03:02 +0000

hbase > alter 'tablename', {NAME => 'ColFamily', VERSIONS => 4}

Answered: What does the following command do in HBase?

Sat, 13 Jun 2020 09:02:48 +0000

hbase > alter 'tablename', {NAME => 'colFamily', METHOD => 'delete'}

This command deletes the column family form the table.

Answered: Give the commands to add a new column family “(newcolfamily”) to a table (“tablename”) which has a existing column family(“oldcolfamily”).

Sat, 13 Jun 2020 09:02:27 +0000

Hbase > disable ‘tablename’

Hbase > alter ‘tablename’ {NAME => ‘oldcolfamily’,NAME=>’newcolfamily’}

Habse > enable ‘tablename’

Answered: What is the Hbase shell command to only 10 records form a tablein HBase?

Sat, 13 Jun 2020 09:02:03 +0000

scan 'tablename', {LIMIT=>10,

STARTROW=>"start_row",

STOPROW=>"stop_row"}

What does the following command doin HBase?

major_compact 'tablename'

Run a major compaction on the table.

Answered: How does Hbase support Bulk data loading in HBase?

Sat, 13 Jun 2020 09:01:44 +0000

There are two main steps to do a data bulk load in Hbase.

Generate Hbase data file(StoreFile) using a custom mapreduce job) from the data source. The StoreFile is created in Hbase internal format which can be efficiently loaded.

The prepared file is imported using another tool like comletebulkload to import data into a running cluster. Each file gets loaded to one specific region.

Answered: How does Hbase provide high availability in HBase?

Sat, 13 Jun 2020 09:01:27 +0000

Hbase uses a feature called region replication. In this feature for each region of a table, there will be multiple replicas that are opened in different RegionServers. The Load Balancer ensures that the region replicas are not co-hosted in the same region servers.

Answered: what is HMaster in HBase?

Sat, 13 Jun 2020 09:01:10 +0000

The Hmaster is the Master server responsible for monitoring all RegionServer instances in the cluster and it is the interface for all metadata changes. In a distributed cluster, it runs on the Namenode.

Answered: What is HRegionServer in HBase?

Sat, 13 Jun 2020 09:00:56 +0000

HRegionServer is the RegionServer implementation. It is responsible for serving and managing regions. In a distributed cluster, a RegionServer runs on a DataNode.

Answered: What are the different Block Caches in HBase?

Sat, 13 Jun 2020 09:00:43 +0000

HBase provides two different BlockCache implementations: the default on-heap LruBlockCache and the BucketCache, which is (usually) off-heap.

Answered: How does WAL help when a RegionServer crashes in HBase?

Sat, 13 Jun 2020 09:00:25 +0000

The Write Ahead Log (WAL) records all changes to data in HBase, to file-based storage. if a RegionServer crashes or becomes unavailable before the MemStore is flushed, the WAL ensures that the changes to the data can be replayed.

Answered: Why MultiWAL is needed in HBase?

Sat, 13 Jun 2020 09:00:09 +0000

With a single WAL per RegionServer, the RegionServer must write to the WAL serially, because HDFS files must be sequential. This causes the WAL to be a performance bottleneck.

Answered: In Hbase what is log splitting in HBase?

Sat, 13 Jun 2020 08:59:49 +0000

When a region is edited, the edits in the WAL file which belong to that region need to be replayed. Therefore, edits in the WAL file must be grouped by region so that particular sets can be replayed to regenerate the data in a particular region. The process of grouping the WAL edits by region is called log splitting.

Answered: How can you disable WAL in HBase? What is the benefit in HBase?

Sat, 13 Jun 2020 08:59:30 +0000

WAL can be disabled to improve performance bottleneck.

This is done by calling the Hbase client field Mutation.writeToWAL(false).

Answered: When do we do manual Region splitting in HBase?

Sat, 13 Jun 2020 08:59:06 +0000

The manual region splitting is done we have an unexpected hotspot in your table because of many clients querying the same table.

Answered: What is a Hbase Store in HBase?

Sat, 13 Jun 2020 08:58:48 +0000

A Habse Store hosts a MemStore and 0 or more StoreFiles (HFiles). A Store corresponds to a column family for a table for a given region.

Answered: Which file in Hbase is designed after the SSTable file of BigTable in HBase?

Sat, 13 Jun 2020 08:58:33 +0000

The HFile in Habse which stores the Actual data(not metadata) is designed after the SSTable file of BigTable.

Answered: Why do we pre-create empty regions in HBase?

Sat, 13 Jun 2020 08:58:16 +0000

Tables in HBase are initially created with one region by default. Then for bulk imports, all clients will write to the same region until it is large enough to split and become distributed across the cluster. So empty regions are created to make this process faster.

Answered: What is hotspotting in HBase?

Sat, 13 Jun 2020 08:57:59 +0000

Hotspotting is asituation when a large amount of client traffic is directed at one node, or only a few nodes, of a cluster. This traffic may represent reads, writes, or other operations. This traffic overwhelms the single machine responsible for hosting that region, causing performance degradation and potentially leading to region unavailability.

Answered: What are the approaches to avoid hotspotting in HBase?

Sat, 13 Jun 2020 08:57:41 +0000

Hotspotting can be avoided or minimized by distributing the rowkeys across multiple regions. The different techniques to do this is salting and Hashing.

Answered: Why should we try to minimize the row name and column name sizes in HBase?

Sat, 13 Jun 2020 08:57:27 +0000

In Hbase values are always freighted with their coordinates; as a cell value passes through the system, it’ll be accompanied by its row, column name, and timestamp. If the rows and column names are large, especially compared to the size of the cell value, then indices that are kept on HBase storefiles (StoreFile (HFile)) to facilitate random access may end up occupying large chunks of the HBase allotted RAM than the data itself because the cell value coordinates are large.

Answered: What is the scope of a rowkey in Hbase?

Sat, 13 Jun 2020 08:57:08 +0000

Rowkeys are scoped to ColumnFamilies. The same rowkey could exist in each ColumnFamily that exists in a table without collision.

Answered: What is the information stored in hbase:meta table in HBase?

Sat, 13 Jun 2020 08:56:52 +0000

The Hbase:meta tables stores details of region in the system in the following format.

info:regioninfo (serialized HRegionInfo instance for this region)

info:server (server:port of the RegionServer containing this region)

info:serverstartcode (start-time of the RegionServer process containing this region)

Answered: What is a Namespace in HBase?

Sat, 13 Jun 2020 08:56:28 +0000

A Namespace is a logical grouping of tables . It is similar to a database object in a Relational database system.

Answered: How do we get the complete list of columns that exist in a column Family in HBase?

Sat, 13 Jun 2020 08:56:14 +0000

The complete list of columns in a column family can be obtained only querying all the rows for that column family.

Answered: When the records are fetched form a Hbase tables, in which order are the sorted in HBase?

Sat, 13 Jun 2020 08:56:00 +0000

The records fetched form Hbase are always sorted in the order of rowkey-> column Family-> column qualifier-> tiestamp.

Answered: What is Next in HBase?

Sat, 13 Jun 2020 08:55:41 +0000

Further you can go through your past assignments you have done with the subject and make sure you are able to speak confidently on them. If you are fresher then interviewer does not expect you will answer very complex questions, rather you have to make your basics concepts very strong.

Second it really doesn't matter much if you could not answer few questions but it matters that whatever you answered, you must have answered with confidence. So just feel confident during your interview. We at tutorialspoint wish you best luck to have a good interviewer and all the very best for your future endeavor. Cheers :-)

What are the step in writing something into Hbase by a client in HBase?

Wed, 10 Jun 2020 14:39:16 +0000

What are the step in writing something into Hbase by a clientin HBase?

Is Hbase a scale out or scale up process in HBase?

Wed, 10 Jun 2020 14:38:36 +0000

Is Hbase a scale out or scale up processin HBase?

What are catalog tables in HBase?

Wed, 10 Jun 2020 14:37:53 +0000

What are catalog tables in HBase?

Name three disadvantages Hbase has as compared to RDBMSin HBase?

Wed, 10 Jun 2020 14:37:06 +0000

Name three disadvantages Hbase has as compared to RDBMSin HBase?

What are the different types of filters used in HBase?

Wed, 10 Jun 2020 14:36:29 +0000

What are the different types of filters used in HBase?

What does the following table do in HBase?

Wed, 10 Jun 2020 14:35:54 +0000

What does the following table do in HBase?

Give a command to check if a table is disabled in HBase

Wed, 10 Jun 2020 14:21:57 +0000

Give a command to check if a table is disabled.

When do we need to disable a table in HBase?

Wed, 10 Jun 2020 14:21:26 +0000

When do we need to disable a table in HBase?

What is the role of Zookeeper in HBase?

Wed, 10 Jun 2020 14:20:46 +0000

What is the role of Zookeeper in HBase?

What is the role of Master server in HBase?

Wed, 10 Jun 2020 14:20:07 +0000

What is the role of Master server in HBase?

How to connect to Hbase?

Wed, 10 Jun 2020 14:19:28 +0000

How to connect to Hbase?