Interview Questions.

Top 100+ Memcached Interview Questions And Answers

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Top 100+ Memcached Interview Questions And Answers

Question 1. What Is Memcached?

Answer :

Memcached is a general motive unfastened and open source, high overall performance, allotted reminiscence object caching system. It is used to hurry up database-driven websites by using caching facts and items in RAM.

In easy words you can say that, Memcached is a part which stores information temporally for 1hour/ 6 hour/ 12 hours/ 1 day etc. And you may combine this thing together with your programs to growth their overall performance.

Question 2. In Which Language Memcached Is Written And Who Is The Author?

Answer :

Memcached is written in "C language" and it is written by Danga Interactive.

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Question three. How Memcached Works?

Answer :

See the subsequent steps to understand how Memcached works:

Memcached first try to get the element of person, Browser send the request to application.
Application calls the Memcached for particular user.
If Result observed in Memcached, Return the result from Memcached.
If Result Not determined in Memcached, Application sends the request to database and keep the result in memcached.
Each Memcached have one unique key.
Get/Set the statistics works on the behalf of key.
You may also delete one or extra keys.
You also can assign tags to 1/greater keys.
Question 4. When The Initial Version Of Memcached First Launched?

Answer :

The first model of Memcached is released on May, 22, 2003.

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Question 5. In Which Websites And Services Memcached Is Generally Used?

Answer :

Memcached can be used for:

Social networking sites for profile caching
For content aggregation i.E. HTML/Page caching
In E-commerce websites for Session and HTML caching
In place primarily based services for database question scaling
In gaming and entertainment offerings for consultation caching
It can also be used to tune cookie/ profile for ad concentrated on.
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Question 6. What Is The Best Usage Of Memcached?

Answer :

Best utilization of Memcached:

It is simple to install in Windows as well as in UNIX working system.
It offers API integration for all the fundamental languages like Java, PHP, C/C++, Python, Ruby, Perl etc.
It complements the overall performance of web software via caching.
It reduces the weight of database server.
It allows you to delete one or greater values.
It helps you to replace the values of keys.
Question 7. What Are The Drawbacks/ Limitations Of Memcached?

Answer :

A listing of barriers or drawbacks of Memcached:

It can't keep information persistently and permanently.
It isn't always a database.
It can not cache large items.
It is not application specific.
It isn't always fault-tolerant or extraordinarily available.
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Question eight. In Which Conditions Cache Cannot Retain The Stored Information?

Answer :

Cache can not retain the stored records in following situations:

When reminiscence allotted for the cache is exhausted.
When object form cache is deleted.
When man or woman object in the cache is expired.
Question nine. Is It Possible To Share A Single Instance Of Memcache Between Multiple Projects?

Answer :

Yes, it's far viable to proportion a single instance of Memcache between more than one tasks because Memcache is a reminiscence shop area and it could be run on one or more servers. You can also run  one-of-a-kind Memcache techniques at the identical host and but they're absolutely impartial.

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Question 10. If You Have Multiple Memcache Servers And One Of The Memcache Server Fails Which Has Your Data, Will It Ever Try To Get Key Data From That One Failed Server?

Answer :

The records in the failed server might not get removed, but there's a provision for car-failure, which can be configured for a couple of nodes. Fail-over may be prompted at some point of any type of socket or Memcached server degree errors and not for the duration of everyday patron mistakes like including an present key, and so on.

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Question 11. How Can You Minimize The Memcached Server Outages?

Answer :

Following are the methods to minimize the Memcached server outage:

When one instance fails, several of them goes down, this could placed large load on the database server whilst the purchaser reloaded the misplaced records. To avoid this, you need to write your code to minimize cache stampedes, it's going to leave a relatively much less impact.

You can convey up an example of Memcached on a new machine using the misplaced machines IP address.

Code is some other choice to limit server outages as it gives you the freedom to trade the Memcached server list with minimum paintings.

Setting timeout price is every other alternative that a few Memcached clients put in force for Memcached server outage. When your Memcached server is going down, the client will maintain looking to ship a request till the time-out restrict is reached.

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Question 12. How Can You Update Memcached When Data Changes?

Answer :

There are  approaches to update Memcached when records changes:

By clearing the cache proactively: You can replace memcached via clearing the cache when an insert or replace is made.

By resetting the cache: It is slightly just like the first approach but in preference to simply deleting the keys and looking forward to the next request for the information to refresh the cache, it resets the values after the insert or update.

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Question thirteen. What Is Dogpile Effect? How To Prevent This Effect?

Answer :

Dogpile impact is a situation whilst cache expires, and websites are hit with the aid of more than one requests made by means of the client at the equal time.

You can prevent this effect with the aid of using semaphore lock. In this gadget when fee expires, first system acquires the lock and starts offevolved generating new value.

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Question 14. If Server Gets Shut Down Then Data Stored In Memcached Is Still Available?

Answer :

In Memcached, facts is not permanently stored. This information is not long lasting so if the server is shut down or restarted then all of the statistics saved in Memcached is deleted.

Question 15. What Is The Difference Between Sap Hana And Memcached?

Answer :

SAP HANA is an in-memory RDBMS and often used for accelerating SAP programs whilst Memcached is a key/fee caching device and used for accessing each RDBMS and NOSQL databases.

Database Administration Interview Questions
Question sixteen. How To Connect Memcached Server With Telnet Command?

Answer :

By the usage of this memcached command:

telnet ostname portNumber

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Question 17. How To Get The Value Of Key?

Answer :

By the use of this command: get key

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Question 18. How To Set The Value Of Key?

Answer :

By the usage of this layout:

set[key][flags][exptim][bytes][noreply]

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Question 19. How To Add Value In Key?

Answer :

By the usage of this format:

add[key][flags][exptim][bytes][noreply]

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Question 20. How To Replace The Value Of Key?

Answer :

By using this layout:

update[key][flags][exptim][bytes][noreply]

Data Structure & Algorithms Interview Questions
Question 21. How To Append The Value Of Key?

Answer :

By the use of this layout:

append[key][flags][exptim][bytes][noreply]

Question 22. How To Prepend Value Of Key?

Answer :

By using this format:

prepend[key][flags][exptim][bytes][noreply]

Question 23. How To Delete The Key?

Answer :

By the usage of this command: delete key

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Question 24. How To Show The Stats?

Answer :

By using this command:

stats

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Question 25. How To Get The Versions?

Answer :

By the usage of this command:

Version

Question 26. How To Close The Connection?

Answer :

By the usage of this command:

Quit

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Question 27. How Would You Update Memcached When Data Changes?

Answer :

There are  methods to replace Memchached while statistics changes:

By clearing the cache proactively: You can replace Memcached by means of clearing the cache while insertion or updation is made.

By resetting the cache: It is slightly just like the primary method but it would not delete the keys and await the subsequent request for the records to refresh the cache, it resets the values after the insert or update.

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Question 28. What Is Dogpile Effect? How Can You Prevent This Effect?

Answer :

If the cache expires, and web sites are hit by means of more than one requests made by means of the patron on the equal time, this effect is known as Dogpile effect.

This effect may be avoided by using the usage of semaphore lock. In this machine whilst cost expires, first technique acquires the lock and starts generating new value.

Question 29. What Happens To The Data Stored In Memcached When Server Accidently Gets Shut Down?

Answer :

In Memcached, data isn't completely stored. It is not a long lasting facts so, if the server is close down or restarted then all the statistics saved in Memcached may be deleted.

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