Interview Questions.

Question 1. What Language Is Couchdb Written In ?

Answer :

Erlang, a concurrent, purposeful programming language with an emphasis on fault tolerance.

Early paintings on CouchDB was started in C++ however turned into replaced through Erlang OTP platform. Erlang has to date established an tremendous match for this assignment.

CouchDB’s default view server uses Mozilla’s Spidermonkey JavaScript library that is written in C. It additionally helps clean integration of view servers written in any language

Question 2. Why Does Couchdb Not Use Mnesia?

Answer :

The first is a storage obstacle of two Giga bytes in step with document.

The second is that it requires a validation and fasten up cycle after a crash or strength failure, so despite the fact that the scale predicament is lifted, the repair up time on massive files is prohibitive.

Mnesia replication is suitable for clustering, but no longer disconnected, allotted edits. Most of the “cool” features of Mnesia aren’t genuinely beneficial for CouchDB.

Also Mnesia isn’t sincerely a preferred-cause, large scale database. It works great as a configuration type database, the type wherein the data isn’t primary to the feature of the utility, but is important for the everyday operation of it. Think things like network routers, HTTP proxies and LDAP directories, things that want to be updated, configured and reconfigured frequently, but that configuration statistics is not often very big.

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Question three. How Do I Use Transactions With Couchdb?

Answer :

CouchDB makes use of an “Optimistic concurrency” version. In the best phrases, this simply means which you send a file version along with your replace, and CouchDB rejects the trade if the cutting-edge file version doesn’t suit what you’ve despatched.

You can re-frame many ordinary transaction based totally eventualities for CouchDB. You do need to form of throw out your RDBMS domain knowledge whilst mastering CouchDB, although.

It’s useful to method issues from a higher degree, instead of attempting to mildew Couch to a SQL based totally international.

Question 4. How Do You Compare Mongodb, Couchdb And Couchbase?

Answer :

MongoDB and CouchDB are report oriented database.
MongoDB and CouchDB are the most traditional consultant of the open source NoSQL database.
They don't have anything in not unusual other than are saved in the record outdoor.
MongoDB and CouchDB, the statistics version interface, object storage and replication strategies have many distinctive.
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Question 5. How Is Pouchdb Different From Couchdb?

Answer :

PouchDB is likewise a CouchDB purchaser, and also you should be capable of transfer among a nearby database or an internet CouchDB instance with out converting any of your application’s code.

However, there are some minor differences to observe:

View Collation – CouchDB uses ICU to reserve keys in a view question; in PouchDB they're ASCII ordered.

View Offset – CouchDB returns an offset belongings within the view outcomes. In PouchDB, offset just mirrors the pass parameter in place of returning a true offset.

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Question 6. So Is Couchdb Now Going To Written In Java?

Answer :

Erlang is a high-quality in shape for CouchDB and I even have in reality no plans to move the venture off its Erlang base. IBM/Apache’s most effective issues are we take away license incompatible 3rd birthday celebration supply code bundled with the venture, a essential requirement for any Apache challenge. So some things may additionally need to replaced within the supply code (probably Mozilla Spidermonkey), but the core Erlang code stays.

An essential purpose is to keep interfaces in CouchDB simple sufficient that developing well matched implementations on different structures is feasible. CouchDB has already inspired the database projects RDDB and Basura. Like SQL databases, I suppose CouchDB wishes opposition and a ecosystem to be feasible long time. So Java or C++ versions is probably created and I could be thrilled to look them, however it likely won’t be me who does it.

Question 7. What Does Ibm’s Involvement Mean For Couchdb And The Community?

Answer :

The major outcomes of IBM’s involvement are:

The code is now being Apache licensed, rather than GPL.
Damien goes to be contributing a great deal greater time!
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Question 8. Mention The Main Features Of Couchdb?

Answer :

JSON Documents – Everything saved in CouchDB boils all the way down to a JSON record.
RESTful Interface – From advent to replication to records insertion, each control and facts mission in CouchDB may be done thru HTTP.
N-Master Replication – You can make use of a limiteless quantity of ‘masters’, making for some very thrilling replication topologies.
Built for Offline – CouchDB can replicate to devices (like Android phones) which could move offline and handle information sync for you while the tool is lower back online.
Replication Filters – You can clear out exactly the records you want to copy to special nodes.
Question 9. What Is The Use Of Couchdb?

Answer :

CouchDB lets in you to write a purchaser side utility that talks without delay to the Couch with out the need for a server facet center layer, substantially decreasing development time. With CouchDB, you could without difficulty manage call for by means of including more replication nodes effectively. CouchDB allows you to replicate the database in your client and with filters you may even mirror that precise consumer’s information.

Having the database stored regionally means your purchaser facet utility can run with nearly no latency. CouchDB will take care of the replication to the cloud for you. Your users may want to get right of entry to their invoices on their cell telephone and make modifications without a considerable latency, all at the same time as being offline. When a connection is gift and usable, CouchDB will routinely replicate those modifications in your cloud CouchDB.

CouchDB is a database designed to run on the net of today for today’s desktop-like programs and the related devices thru which we get right of entry to the net.

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Question 10. How Much Stuff Can Be Stored In Couchdb?

Answer :

For node partitioning, essentially limitless. The realistic scaling limits for a unmarried database example,  are not but known.

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Question eleven. What Is Couchdb Kit?

Answer :

The Couchdb Kit is used to provide a structure on your Python applications to control and get entry to Couchdb. This package gives full featured  and easy customer to control and get right of entry to Couchdb. It lets you maintain databases,  to view get entry to, Couchdb server and doc managements. Mostly python items are meditated by way of the gadgets for comfort. The Database and server objects are used easily  as the usage of a dict.

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Question 12. How Can I Get A List Of The Design Documents In A Database?

Answer :

Query the _all_docs view with

startkey="_design/"&endkey="_design0".

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Question thirteen. Can Views Update Documents Or Databases?

Answer :

No. Views are constantly read­only to databases and their files.

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Question 14. Where Are The Couchdb Logfiles Located?

Answer :

For a default linux/unix installation the logfiles are located right here:

/usr/local/var/log/couchdb/sofa.Log

This is ready within the default.Ini file located here:

/and so forth/couchdb/default.Ini 

If you've installed from source and are jogging couchdb in dev mode the logfiles are placed here:

YOUR­COUCHDB­SOURCE­DIRECTORY/tmp/log/couch.Log 

Question 15. What Is Couchdb?

Answer :

CouchDB is a database that absolutely embraces the web. Store your data with JSON files. Access your files and query your indexes along with your net browser, thru HTTP. Index, combine, and transform your files with JavaScript. CouchDB works nicely with modern-day net and mobile apps. You can even serve internet apps immediately out of CouchDB. And you may distribute your records, or your apps, successfully the usage of CouchDB’s incremental replication. CouchDB helps grasp-master setups with automatic war detection.

CouchDB comes with a set of functions, which includes on-the-fly file transformation and real-time change notifications, that makes web app development a breeze. It even comes with an easy to use internet administration console. You guessed it, served up without delay out of CouchDB! We care a lot approximately dispensed scaling. CouchDB is especially to be had and partition tolerant, however is also subsequently steady. And we care loads approximately your data. CouchDB has a fault-tolerant garage engine that places the protection of your data first.

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Question 16. What Does Couch Mean?

Answer :

It's an acronym, Cluster Of Unreliable Commodity Hardware. This is a announcement of Couch's long term dreams of large scalability and high reliability on fault inclined hardware. The disbursed nature and flat deal with space of the database will permit node partitioning for garage scalability (with a map/reduce fashion query facility) and clustering for reliability and fault tolerance.

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Question 17. Is Couchdb Ready For Production?

Answer :

Yes. There are many agencies using CouchDB. 

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Question 18. What Platforms Are Supported?

Answer :

Most POSIX structures, this includes GNU/Linux and OS X.
Windows is not officially supported but it have to work 
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Question 19. How Do I Do Sequences?

Answer :

With replication sequences are hard to realise. Sequences are often used to make sure unique identifiers for every row in a database desk. CouchDB generates precise ids from its own and you could specify your own as nicely, so that you don't really want a chain right here. If you operate a chain for some thing else, you may discover a way to express in CouchDB in another manner.

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Question 20. How Do I Use Replication?

Answer :

POST /_replicate with a put up frame of 
"source":"$source_database"
,
"goal":"$target_database"

Where $source_database and $target_database can be the names of local database or full URIs of faraway databases. Both databases want to be created before they may be replicated from or to. 

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Question 21. How Do I Review Conflicts Occurred During Replication?

Answer :

Use a view like this:

map: feature(doc) if(doc._conflicts)emit(null,null)? 

Question 22. How Can I Spread Load Across Multiple Nodes?

Answer :

Using an http proxy like nginx, you could load balance GETs across nodes, and direct all POSTs, PUTs and DELETEs to a grasp node. CouchDB's prompted replication facility can preserve more than one study-handiest  servers in sync with a unmarried grasp server, so through replicating from grasp ­> slaves on a regular basis, you may preserve your content material up to date.

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Question 23. Can I Talk To Couchdb Without Going Through The Http Api?

Answer :

CouchDB's facts version and internal API map the REST/HTTP version so nicely that some other API could essentially reinvent some flavor of HTTP. However, there's a plan to refractor CouchDB's internals so as to provide a documented Erlang API. 

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Question 24. Erlang Has Been Slow To Adopt Unicode. Is Unicode Or Utf­8 A Problem With Couchdb?

Answer :

CouchDB makes use of Erlang binaries internally. All facts coming to CouchDB need to be UTF­eight encoded. 

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Question 25. How Fast Are Couchdb Views?

Answer :

It could be pretty tough to give out any numbers that make a lot feel. From the structure factor of view, a view on a desk is much like a (multi­column) index on a desk in an RDBMS that simply plays a short look­up. So this theoretically must be quite quick. The major advantage of the structure is, however, that it's miles designed for high visitors. No locking takes place within the storage module (MVCC and all that) allowing any wide variety of parallel readers in addition to serialized writes. With replication, you could even set up a couple of machines for a horizontal scale­out and records partitioning (within the destiny) will can help you cope with huge volumes of information

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