Apache CouchDB

Apache CouchDB is open-source database software that focuses on ease of use and having a scalable architecture. We have list down some Interview questions on CouchDB which will help you to prepare for different IT interviews like, Fullstack Developer, Technical lead, technical manager, and data analyst etc.

Q.1 Define CouchDB.
CouchDB refers to a documented database server accessible via a RESTful JSON API. This is distributed, robust, incremental replication with bi-direction. This uses JSON for storing data, JavaScript as its query language for transforming the documents, using MapReduce, and HTTP for an API. Further, it is replicated across multiple server instances ad offers various libraries for the language of your choice.
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Q.2 Name the language in which CouchDB can be written.
CouchDB is written in Erlang which is a concurrent, functional programming language that focuses on fault tolerance. This is used for building massively scalable soft real-time systems with requirements of high availability. However, some of its parts are written in C language too.
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Q.3 Which language was first used in CouchDB?
CouchDB’s work was started in C++ language. But later, it was replaced by the Erlang OTP platform.
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Q.4 Differentiate between CouchDB and SQL databases.
In CouchDB, JSON-based document formats are used for storing data, JavaScript for MapReduce indexes, and regular HTTP of its API. This includes the Couch database that is used for storing data in the JSON document. In this, you query your index and documents with the help of a web browser via HTTP. This is implemented in the Erlang programming language While SQL database uses RDBMS for storing data. It is a very fast, Multi-user, Multi-thread, and robust SQL (structured query language) database server. This is also used for big data storage of a large project. Further, it is a NoSQL database with manual transmission. This is implemented in C, C++ programming languages.
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Q.5 What are the key features of CouchDB?
The key features of CouchDB are -
1. JSON Documents – Everything stored in CouchDB boils down to a JSON document.
2. RESTful Interface – From creation to replication to data insertion, every management and data task in CouchDB can be done via HTTP.
3. N-Master Replication – You can make use of an unlimited amount of ‘masters’, making for some very interesting replication topologies.
4. Built for Offline – CouchDB can replicate to devices (like Android phones) that can go offline and handle data sync for you when the device is back online.
5. Replication Filters – You can filter precisely the data you wish to replicate to different nodes.
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Q.6 What are the features that make CouchDB popular?

Yes, CouchDB is very popular nowadays, and many companies are using CouchDB. This comes with features such as:

  • Firstly, it can be replicated across multiple server instances.
  • Secondly, it offers various libraries for the language of your choice.
  • Thirdly, it provides fast indexing and retrieval
  • Then, it has a REST-like interface for document insertion, updates, recovery, and deletion.
  • Lastly, it has the support for JSON-based document format which can easily be translatable over different languages.
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Q.7 What do you understand by Couchbase server?
Cloudbase server is primarily a NoSQL database that is faster, elastic, as well as easy to use. This is regarded as one of the finest oriented-database software package. This is considered for the collective application that has multiple uses and are widely adopted in the modern day approaches.
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Q.8 Is there any similarity between MongoDB and CouchDB?
MongoDB and CouchDB both are document-oriented databases. They both can be considered as an example of an open-source NoSQL database as both are Schema-free. Further, they both support JavaScript, can be used in queries, support aggregation functions such as MapReduce, and sent the database to execute it. Lastly, they can work on common programming languages like C, C#, Erlang, Java, JavaScript, Ruby, Python, Haskell, PHP, Perl, etc.
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Q.9 Given an open source technology what are the other good things that you know about the Cloudbase?
Apart from being an open source technology, the Couchbase was released under Apache 2.0 license. Couchbase comes with a community and an enterprise edition with multiform capabilities that make it good enough to be considered for the long run.
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Q.10 Name the major elements that CouchDB offers.
The components include: JSON Documents RESTful Interface N-Master Replication Built for Offline Replication Filters ACID semantics Document storage Authentication and Session Support Security Map/Reduce List and Show
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Q.11 Is it important to create a data bucket in the system?
It is important to create a data bucket in the system. This is usually done as the server only prefers the data buckets when it comes to storing the data. When the server is installed, the default bucket gets created automatically.
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Q.12 Differentiate between PouchDB and CouchDB.
PouchDB is also a CouchDB client, in which you can switch between a local database or an online CouchDB instance without changing any of your application’s code. However, CouchDB uses ICU for ordering keys in a view query, and in PouchDB they are ASCII ordered. Further, CouchDB returns an offset property in the view results. Whereas, in PouchDB, offset just mirrors the skip parameter instead of returning a true offset.
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Q.13 How do you define data manager in the Couchbase Server?
Data Manager in the Couchbase Server is a functional block with some useful applications. It is primarily responsible for the purpose of extracting, as well as storing the data from the applications. Data manager in the Couchbase Server is also responsible for other crucial tasks which it perform and without making an impact of the overall functionality of the software
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Q.14 Define CouchdbKit.
Couchdbki provides a framework for Python applications to access and manage Couchdb. It offers a full-featured and easy client for accessing and managing CouchDB. Moreover, it enables users to manage a CouchDB server, databases, doc management, and view access. Examples include server and databases objects.
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Q.15 How do you define VBucket?
vBucket is defined as a logical ways of partitioning data due to the natural condition. Such that it is distributed over all the nodes in the clusters. The couchbase type bucket which gets designed in a group is split up automatically in a static group of slices after which, the buckets map to the individual server. VBuckets are designed and used to assign information more effectively.
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Q.16 Why there is no use of Mnesia in CouchDB?
Firstly, there is a storage limitation of 2 Gigabytes per file. Secondly, it requires validation and a fix-up cycle after a crash or power failure, so even if the size limitation is lifted, the fix-up time on large files is prohibitive. Thirdly, Mnesia replication is best suitable for clustering, but not for disconnected and distributed edits. Lastly, it only works best as a configuration type database, the type where the data isn’t central to the function of the application but is necessary for the normal operation.
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Q.17 Define the strict upper limit on the storage capacity of a data bucket in Couchbase Server?
Each data bucket is having a limit of 20MB. Such that in case more storage is required, the same can be considered by talking the additional buckets into consideration.
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Q.18 How to use transactions with Couchdb?
CouchDB uses an “Optimistic concurrency” model in which you send a document version along with your update. However, CouchDB rejects the change if the current document version doesn’t match what you’ve sent. And, you can replan many normal transaction-based scenarios for CouchDB with any need for sorting or throwing out your RDBMS domain knowledge.
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Q.19 What are the elements present in Couchbase Node?
Each Couchbase Node contains four elements -
1. Index Service
2. Data Service
3. Cluster Manager component
4. Query Service
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Q.20 Can you define IBM’s Involvement in CouchDB?
The main outcomes of IBM’s involvement are: Firstly, the code is now being Apache-licensed, instead of GPL. Secondly, Damien is going to be contributing more time.
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Q.21 What is data replication?
Data Replication is defined as a term that defines the same type of data is present at multiple locations in the server. Such that the same can put unnecessary burden on the performance and sometime, it takes additional cost for the organization.
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Q.22 Is it possible to view update the documents or databases?

No, views are always read-only for databases and their documents. However, views are used for the following purpose:

  • Firstly for filtering the document from the database to find relevant data for a particular process.
  • Secondly, for extracting data from documents and display it in a specific order.
  • Then, for creating indexes to find the document by any value or structure that remains in them and use these indexes to represent the relationship between documents.
  • Lastly, making all sorts of calculations on the data in your documents
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Q.23 Name the type of platforms supported in CouchDB.
CouchDB supports POSIX systems like GNU/Linux and OS X.
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Q.24 Define sequences.
Sequences are used for ensuring the unique identifiers for each row in a database table. They are difficult to realize with replication. But, CouchDB creates unique ids on its own, and you can define your own as well, so you don't need a sequence here.
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Q.25 Explain the replication process.
Replication synchronizes two copies of the same database which reside on the same server or can be live on two different servers. However, if you change one copy of the database, replication will send the details to another copy. For performing replication, firstly send a request of HTTP to CouchDB with a source, and a target database and CouchDB will send the changes from source to target. POST /_replicate with a post body of {"source":"$source_database" , "target":"$target_database"}
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Q.26 How to communicate to CouchDB without going via HTTP/ API?
CouchDB's data model and internal API plan the REST/HTTP model in a very simple way that any other API would take over some features of HTTP. However, there is a design to refractor CouchDB's internals to provide a documented Erlang API.
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Q.27 Describe the process for spreading the load over multiple nodes?
Using an HTTP proxy like Nginx, you can load balance GETs over nodes, and direct all POSTs, PUTs, and DELETEs to a master node. However, CouchDB's triggered replication facility can hold on to multiple read-only servers in sync with a single master server, so by replicating from master on a regular basis, you can keep your content up to date.
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Q.28 Erlang is quite slow while adopting Unicode. Is Unicode Or Utf­8 an issue in Couchdb?
CouchDB uses Erlang binaries internally. That is to say, all data coming to CouchDB must be UTF­8 encoded.
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Q.29 Define ETL Testing and Manual Testing.
ETL testing is the basic procedure of writing scripts for the automated testing process without any need for any additional technical knowledge other than the software. This testing is one of the fast and systematic testings that gives the top result. And, Manual testing uses other testing and seeing the procedure and needs a technical knowledge of SQL and shell scripting. This is a time and efforts consuming procedure that can result in an error.
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Q.30 Define cubes and OLAP cubes.
Cubes are the data processing units that contain the facts and dimensions from the database. They provide multi-dimensional analysis. On the other hand, OLAP stands for Online Analytics processing which is used for storing a large amount of data in a multi-dimensional form that can be used for reporting purposes.
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Q.31 Name the components of couchbase Node.
Components of couchbase Nodes are: Data service Index service Cluster manager component Query service
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Q.32 Name the functional blocks used in couchbase server?

The functional blocks used in couchebase server are:

  • Data manager
  • Cluster manager
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Q.33 Define N1Ql stand.
N1QI stands for the non-first usual form of the query language. This is designed for manipulating JSON data in the Couchbase server. Some of its statements to operate the JSON data are: INSERT DELETE MERGE SELECT UPDATE
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Q.34 Define a shared server.
Organizations and businesses these days have the option to consider a server that is only dedicated to them. A shared server is distributed among many businesses and it hosts a lot of businesses. The shared hosting is cost-efficient as compared to a dedicated server. This is best for businesses with small data needs and basic applications.
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Q.35 Define VBucket.
When the data requires to be divided or a portioning is performed in a logical manner, then VBucket approach is adopted. All the buckets present in the Couchbase get split automatically if this option is enabled by the user. However, using this, users can simply ensure the effective allocation of the data throughout a cluster.
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Q.36 Can you tell the upper limit on the storage capacity of a data bucket in Couchbase Server?
Every data bucket have a limit of 20MB. If the user wants to have more storage, the same can be considered by taking the additional buckets into consideration.
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Q.37 Define data replication.
Data Replication is a term that specifies the same type of data present at multiple locations in the server. The same can put an unnecessary load on the performance and even takes additional costs for the organization.
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Q.38 How can we easily locate a document in the Couchbase?
We can easily locate a document in the Couchbase by considering the JSON format.
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Q.39 Can you name the ports for accepting or listening to the requests?

There are two TCP ports that are used for listening to requests:

  • Port 11210
  • Port 11211
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Q.40 Define a document in the context of a database.
This can be considered as an entry made to a database. A document can have a defined ID related to it and the same can be used for locating the document in the server. The real application data remains in the document and the same can be accessed anytime by the user. Moreover, documents also provide basic information about a defined task.
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Q.41 Is there any chance of Couchbase server failure?
There is very little chance of server failure in couchbase. Some of the failure cause can be: Firstly, power failure Secondly, no maintenance of the server Thirdly, the presence of ominous data Next, improper Integration or hacking related issues Lastly, slow bandwidth
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Q.42 Define Cross Datacenter Replication.
Cross Datacenter Replication or XDCR helps in providing a smooth mode for replicating data from one set to another. They require replicating active data to N+1 Server clusters, or even external apps like Spark, Elastic, Storm, and so forth. further, the sets are used for various geographical data centers. They are used either for bringing data closer to customers for fast data access or for recovery of any disaster.
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Q.43 What are the subsystems that function on each node?

There are four subsystems that function on each node:

1. Pulses These are the set of words are exchanged by the Watchdog developers regularly. The exchanging process is carried forward with the chosen cluster head in order for providing well-being revises.

2. Worldwide Singleton Supervisor This is a subsystem that is tasked with selecting the cluster heads only in case the previously voted head stops.

3. Progression Monitor This helps in monitoring in carrying out the limited executive.

4. The Pattern Manager In this, every node in the set features a defined pattern. This receives, monitors, and processes the local configuration.

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Q.44 Define Data Manager and Cluster Manager in Couchbase Server.
  • Data Manager They are responsible for extracting and storing the data from apps. They reveal two ‘memcapable’ docks inside the sets of connections in which the non-vBucket aware client libraries are guided by 1 port. On the opposite, the vBucket aware client libraries will be guided by another one. However, all data manager code has been written in the C and C++ programming languages.
  • Cluster Manager This is designed for looking after the performance as well as the arrangement of the nodes in the couchbase server cluster. The Manager's code will be running on every block in clusters. Then, it selects the node for the purpose of aggregation. Lastly, all Cluster Manager Code has been written in Erlang/OTP.
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Q.45 Can we boost the access to any database document by catching it in memory automatically using Couchbase?
Yes, Couchbase has the ability to speed up access to any database document by automatically catching it in the memory.
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Q.46 Define Object-managed Cache in the Couchbase Server.
Couchbase Server contains an object-managed, built-in, and multi-threaded cache. This has the ability to implement APIs that are Memcached compatible. For example, append, prepend, set, get, etc.
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Q.47 What do you understand about data structures in the Couchbase server?
In Couchbase, Data structures have the same concept as those included in javascript. In this, Map is a key-value structure that is the same as a JavaScript Object. However, in Map, a value is accessed by employing the key string. And, one can place the values at the very start or at the end which can be accessed using numerical indexes.
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Q.48 Define ETL process.
ETL stands for Extracting, Transforming and Loading of data from any system to the destination. This performs data integration process as: Firstly, Extracting. In this, we locate the data and then removing source file. Secondly, Transforming. This is the process of transporting the file to the required target. Lastly, Loading. This means loading the file in the target system in the format applicable.
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Q.49 Name some of the ETL tools.
The tools that are used in Extracting, Transforming and Loading (ETL) are:- Business Objects XI SAS business warehouse Cognos Decision Stream Oracle Warehouse Builder SAS Enterprise ETL server
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Q.50 How will you improve CouchDB performance?
  • Firstly, we can try using the built-in Erlang functions like _sum , _count , instead of writing Javascript. Since complex views can take alot of time.
  • Also, try to post such not too complex map/reduce.
  • Lastly, do not forget: indexing all docs is only done once after changing the view (or pushing a whole bunch of new docs)
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