Interview Questions.

Question 1. Explain What Is Hbase?

Answer :

Hbase is a column-oriented database management device which runs on pinnacle of HDFS (Hadoop Distribute File System). Hbase isn't a relational facts keep, and it does no longer guide based question language like SQL.

In Hbase, a master node regulates the cluster and region servers to store quantities of the tables and operates the work on the facts.

Question 2. What Are The Different Commands Used In Hbase Operations?

Answer :

There are five atomic commands which carry out specific operations by using Hbase.Get, Put, Delete, Scan and Increment.

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Question three. Explain Why To Use Hbase?

Answer :

High potential storage system
Distributed design to cater large tables
Column-Oriented Stores
Horizontally Scalable
High overall performance & Availability
Base goal of Hbase is tens of millions of columns, thousands of variations and billions of rows
Unlike HDFS (Hadoop Distribute File System), it supports random real time CRUD operations
Question 4. How To Connect To Hbase?

Answer :

A connection to Hbase is installed via Hbase Shell that's a Java API.

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Question 5. Mention What Are The Key Components Of Hbase?

Answer :

Zookeeper: It does the co-ordination work among patron and Hbase Maser

Hbase Master: Hbase Master monitors the Region Server
RegionServer: RegionServer video display units the Region
Region: It contains in memory records store(MemStore) and Hfile.
Catalog Tables: Catalog tables encompass ROOT and META
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Question 6. What Is The Role Of Master Server In Hbase?

Answer :

The Master server assigns areas to vicinity servers and handles load balancing in the cluster.

Question 7. Explain What Does Hbase Consists Of?

Answer :

Hbase includes a fixed of tables
And every desk consists of rows and columns like conventional database
Each table must incorporate an detail described as a Primary Key
Hbase column denotes an attribute of an item
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Question 8. What Is The Role Of Zookeeper In Hbase?

Answer :

The zookeeper keeps configuration information, provides allotted synchronization, and additionally continues the communication between clients and area servers.

Question nine. Mention How Many Operational Commands In Hbase?

Answer :

Operational command in Hbases is ready five types:

Get
Put
Delete
Scan
Increment
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Question 10. When Do We Need To Disable A Table In Hbase?

Answer :

In Hbase a table is disabled to allow it to be modified or exchange its settings. .When a desk is disabled it cannot be accessed via the scan command.

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Question eleven. Explain What Is Wal And Hlog In Hbase?

Answer :

WAL (Write Ahead Log) is much like MySQL BIN log; it records all of the adjustments occur in information. It is a trendy collection file by way of Hadoop and it shops HLogkey’s. These keys consist of a sequential quantity as well as real statistics and are used to replay now not but endured records after a server crash. So, in coins of server failure WAL work as a lifestyles-line and retrieves the lost information’s.

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Question 12. What Are The Different Types Of Filters Used In Hbase?

Answer :

Filters are used to get unique facts shape a Hbase table rather than all the information.

They are of the following kinds.

Column Value Filter
Column Value comparators
KeyValue Metadata filters.
RowKey filters.
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Question thirteen. In Hbase What Is Column Families?

Answer :

Column households comprise the simple unit of bodily storage in Hbase to which features like compressions are implemented.

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Question 14. Name Three Disadvantages Hbase Has As Compared To Rdbms?

Answer :

Hbase does not have in-built authentication/permission mechanism
The indexes may be created most effective on a key column, but in RDBMS it can be accomplished in any column.
With one HMaster node there may be a single factor of failure.
Question 15. Explain What Is The Row Key?

Answer :

Row secret is defined through the application. As the mixed secret is pre-constant by using the rowkey, it permits the application to outline the desired sort order. It additionally permits logical grouping of cells and make sure that all cells with the identical rowkey are co-positioned on the equal server.

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Question sixteen. Is Hbase A Scale Out Or Scale Up Process?

Answer :

Hbase runs on pinnacle of Hadoop that is a disbursed machine. Haddop can handiest scale uo as and while required by way of including extra machines at the fly. So Hbase is a scale out procedure.

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Question 17. Explain Deletion In Hbase? Mention What Are The Three Types Of Tombstone Markers In Hbase?

Answer :

When you delete the cellular in Hbase, the statistics isn't always certainly deleted but a tombstone marker is set, making the deleted cells invisible. Hbase deleted are simply removed at some point of compactions.

Three types of tombstone markers are there:

Version delete marker: For deletion, it marks a unmarried model of a column
Column delete marker: For deletion, it marks all the versions of a column
Family delete marker: For deletion, it marks of all column for a column circle of relatives
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Question 18. What Are The Step In Writing Something Into Hbase By A Client?

Answer :

In Hbase the consumer does not write at once into the HFile. The consumer first writes to WAL(Write Access Log), which then is accessed via Memdtore. The Memstore Flushes the statistics into everlasting reminiscence every so often.

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Question 19. Explain How Does Hbase Actually Delete A Row?

Answer :

In Hbase, anything you write may be stored from RAM to disk, these disk writes are immutable barring compaction. During deletion procedure in Hbase, foremost compaction method delete marker while minor compactions don’t. In ordinary deletes, it consequences in a delete tombstone marker- these delete records they represent are removed at some point of compaction.

Also, if you delete facts and upload more facts, however with an earlier timestamp than the tombstone timestamp, in addition Gets may be masked via the delete/tombstone marker and subsequently you may no longer receive the inserted fee until after the most important compaction.

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Question 20. What Is Compaction In Hbase?

Answer :

As increasingly more data is written to Hbase, many HFiles get created. Compaction is the method of merging these HFiles to 1 document and after the merged document is created successfully, discard the old file.

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Question 21. Explain What Happens If You Alter The Block Size Of A Column Family On An Already Occupied Database?

Answer :

When you alter the block length of the column circle of relatives, the new records occupies the new block size while the antique data remains within the vintage block size. During facts compaction, vintage statistics will take the new block size. New files as they're flushed, have a new block size whereas current statistics will remain read successfully. All data have to be transformed to the brand new block size, after the subsequent fundamental compaction.

Question 22. What Are The Different Compaction Types In Hbase?

Answer :

There are two forms of compaction. Major and Minor compaction. In minor compaction, the adjacent small HFiles are merged to create a single HFile with out eliminating the deleted HFiles. Files to be merged are selected randomly.

In Major compaction, all of the HFiles of a column are emerged and a single HFiles is created. The delted HFiles are discarded and it's far usually caused manually.

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Question 23. What Is A Cell In Hbase?

Answer :

A cell in Hbase is the smallest unit of a Hbase table which holds a chunk of records within the form of a tuplerow,column,model

Question 24. What Is The Scope Of A Rowkey In Hbase?

Answer :

Rowkeys are scoped to ColumnFamilies. The identical rowkey ought to exist in every ColumnFamily that exists in a table without collision.

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Question 25. What Is The Role Of The Class Hcolumndescriptor In Hbase?

Answer :

This elegance is used to save data approximately a column circle of relatives along with the wide variety of versions, compression settings, etc. It is used as enter when growing a desk or adding a column.

Question 26. What Is A Namespace In Hbase?

Answer :

A Namespace is a logical grouping of tables . It is much like a database object in a Relational database device.

Question 27. What Is The Lower Bound Of Versions In Hbase?

Answer :

The lower sure of variations shows the minimal wide variety of versions to be saved in Hbase for a column. For instance If the price is ready to three then 3 modern day model wil be maintained and the older ones may be removed.

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Question 28. What Is Hotspotting In Hbase?

Answer :

Hotspotting is a scenario while a massive quantity of consumer traffic is directed at one node, or only some nodes, of a cluster. This traffic may constitute reads, writes, or other operations. This site visitors overwhelms the unmarried machine chargeable for website hosting that place, causing performance degradation and doubtlessly main to region unavailability.

Question 29. What Is Ttl (time To Live) In Hbase?

Answer :

TTL is a data retention method the use of which the version of a cell can be preserved till a specific term.Once that timestamp is reached the specific model might be eliminated.

Question 30. Why Do We Pre-create Empty Regions?

Answer :

Tables in HBase are to begin with created with one vicinity through default. Then for bulk imports, all clients will write to the equal area until it is big enough to split and end up distributed throughout the cluster. So empty areas are created to make this system quicker.

Question 31. Does Hbase Support Table Joins?

Answer :

Hbase does now not guide desk joins. But the usage of a mapreduce process we can specify be a part of queries to retrieve information from more than one Hbase tables.

Question 32. Which File In Hbase Is Designed After The Sstable File Of Bigtable?

Answer :

The HFile in Habse which stores the Actual records(no longer metadata) is designed after the SSTable report of BigTable.

Question 33. What Is A Hbase Store?

Answer :

A Habse Store hosts a MemStore and 0 or extra StoreFiles (HFiles). A Store corresponds to a column circle of relatives for a table for a given region.

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Question 34. What Are The Two Types Of Table Design Approach In Hbase?

Answer :

They are:

Short and Wide
Tall and Thin
Question 35. When Do We Do Manual Region Splitting?

Answer :

The guide location splitting is finished we've an surprising hotspot on your desk because of many customers querying the equal desk.

Question 36. In Which Scenario Should We Consider Creating A Short And Wide Hbase Table?

Answer :

The short and huge desk design is taken into consideration whilst there's

There is a small range of columns
There is a large variety of rows
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Question 37. In Hbase What Is Log Splitting?

Answer :

When a vicinity is edited, the edits inside the WAL report which belong to that area want to be replayed. Therefore, edits in the WAL document ought to be grouped through region so that particular sets may be replayed to regenerate the information in a particular location. The procedure of grouping the WAL edits by way of location is referred to as log splitting.

Question 38. How Does Hbase Support Bulk Data Loading?

Answer :

There are two primary steps to do a facts bulk load in Hbase:

Generate Hbase facts file(StoreFile) the usage of a custom mapreduce job) from the records source. The StoreFile is created in Hbase inner layout which may be effectively loaded.
The prepared document is imported the use of any other device like comletebulkload to import statistics right into a going for walks cluster. Each document receives loaded to at least one particular region.
Question 39. Why Multiwal Is Needed?

Answer :

With a single WAL in keeping with RegionServer, the RegionServer need to write to the WAL serially, because HDFS files have to be sequential. This causes the WAL to be a performance bottleneck.

Question 40. How Does Hbase Provide High Availability?

Answer :

Hbase makes use of a feature known as location replication. In this feature for every region of a table, there can be multiple replicas which might be opened in distinctive RegionServers. The Load Balancer ensures that the vicinity replicas are not co-hosted within the identical region servers.

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Question 41. How Does Wal Help When A Regionserver Crashes?

Answer :

The Write Ahead Log (WAL) data all modifications to statistics in HBase, to document-based garage. If a RegionServer crashes or will become unavailable earlier than the MemStore is flushed, the WAL ensures that the changes to the records may be replayed.

Question 42. What Is Hregionserver In Hbase?

Answer :

HRegionServer is the RegionServer implementation. It is chargeable for serving and coping with regions. In a distributed cluster, a RegionServer runs on a DataNode.

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Question forty three. What Are The Different Block Caches In Hbase?

Answer :

HBase presents two specific BlockCache implementations: the default on-heap LruBlockCache and the BucketCache, that's (commonly) off-heap.