What Is Servlet Collaboration
The process of communicating information among the servlets of a Java web application is known as servlet collaboration. This enables data to be transmitted from one servlet to another via method invocations. Java’s Servlet API , which exposes two interfaces, is the primary method for achieving Servlet Collaboration.
These two interfaces contain the approaches for achieving the purpose of servlet information exchange.
Work Through System Design Interview Questions
As you likely noticed in section 1, we recommend using a repeatable answer framework when answering system design interview questions. You can learn more about that framework here, but in the meantime, here is a summary:
Step 1: Ask clarifying questions
First, spend about five minutes checking in with your interviewer about the functional and non-functional requirements of what youre going to design. Ask about the systems goals and how they will be measured. Be sure that you fully understand the question before moving forward.
Step 2: Design high-level
Start the high-level design by specifying one to two metrics . Then use these metrics to do some simple calculations in order to find the optimal usage pool of the system.
Once youve defined your metrics, map out only the most functional components of the system .
Finally, before getting into the more detailed aspects of your system, make some decisions on how you will design its database. Choose whether it will be a relational or a no-SQL database, as well as its metadata and table structure.
Step 3: Drill down on your design
If you havent already, start mapping out the system on your whiteboard. Speak through your diagram so that your interviewer is able to follow along and ask questions when necessary.
Consider any bottlenecks that may arise when it comes to the systems scalability, performance, or flexibility.
Step 4: Bring it all together
How To Stand Out In Uber Interviews
Understand Uberâs Business Model: Itâs important for you to understand how Uberâs apps like Uber Eats, Uber Freight, and Uber Elevate work to ask better and intelligent questions to the interviewer.
Donât Hesitate to Grill Your Interviewer: Hiring Managers at Uber look for candidates who ask challenging questions and provide better solutions for their models. Theyâre interested in working with people who have good analytical skills.
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How To Handle The Datacenter Failure
Datacenter failure doesnt happen very often but Uber still maintains a backup data center to run the trip smoothly. This data center includes all the components but Uber never copies the existing data into the backup data center.
Then how does Uber tackle the data center failure??
It actually uses driver phones as a source of trip data to tackle the problem of data center failure. When The drivers phone app communicates with the dispatch system or the API call is happening between them, the dispatch system sends the encrypted state digest to the drivers phone app. Every time this state digest will be received by the drivers phone app. In case of a data center failure, the backup data center doesnt know anything about the trip so it will ask for the state digest from the drivers phone app and it will update itself with the state digest information received by the drivers phone app.
Want to get a Software Developer/Engineer job at a leading tech company? or Want to make a smooth transition from SDE I to SDE II or Senior Developer profiles? If yes, then youre required to dive deep into the System Design world! A decent command over System Design concepts is very much essential, especially for the working professionals, to get a much-needed advantage over others during tech interviews.
What Do You Know About Demand Paging In Operating Systems
Demand paging in operating systems is a strategy for loading pages . A page frame is the smallest contiguous unit of physical memory with a predetermined length into which the operating system maps memory pages) only when they are needed. Virtual Memory is a storage allocation method that makes it possible to address secondary memory as if it were the main memory. The addresses used by a program to refer to memory are different from the addresses used by the memory system to designate physical storage sites, and the addresses created by the program are automatically converted to machine addresses. The quantity of secondary memory available is defined by the number of main storage sites available rather than the actual number of main storage locations, and the capacity of virtual storage is restricted by the computer system’s addressing scheme.
When a place on the page is addressed during execution, the page is only brought into memory. The following are the steps for getting a page into the main memory or demand paging:
Also Check: Backend Developer Technical Interview Questions
Write Functional Code For Solving The Problem Given Below
“You have been given the string s and the integer k. You can replace any character in the string with another uppercase English character. This operation can be performed at most k times. After executing the preceding procedures, return the length of the longest substring containing the same letter.”
Sample input and output is shown below:
Input: s = “AABABBA”, k = 1Output: 4
C ++ function which solves the given Data Structures and Algorithm problem is given below:
int replaceCharacters maxLength = max } return maxLength }
In this question, we use the sliding window technique along with two pointers “l” and “r” to get our answer. We keep moving the pointer “r” by one from left to right each iteration and update the frequency of all characters in the window starting from index l to r. If the difference of the subarray length l to r and maximum frequency among all the characters in the window of l to r is greater than the given value k, we move l forward until the same condition does not hold . In the end, we update our answer variable with the value of the length of the subarray “r – l + 1” since we can guarantee that after performing at most k op, all characters in the subarray can be made the same.
Advanced Issues And Considerations
Fault Tolerance and Replication
What if a Driver Location server or Notification server dies? We will need server replicas so that a secondary server can take control when needed. We can also store data in a persistent storage like SSDs to provide fast IOs.
This way, if both our primary and secondary servers die, we can quickly recover data from the persistent storage.
Uber also provides a ranking system for drivers, where a customer can rate a driver according to wait times, courtesy, and safety. Say we want to rank search results by popularity or relevance a well as proximity.
We need to return top rated drivers within a given radius. Assume we track the ratings of drivers in a database and QuadTree. An aggregated number will represent popularity in the system based on the star ratings.
So, while the system searches for the top 10 drivers within a given radius, we also ask each partition of the QuadTree to return the top drivers with a specified rating. The aggregator server will determine the top 10 drivers among all drivers returned by different partitions.
Other issues to discuss
- How will we handle clients using slow or disconnecting networks?
- What if a client gets disconnected when they are a part of a ride?
- How will we handle billing if a ride if disconnected?
- How can new machine learning components be implemented to improve this system?
Design A Traffic Violation System
This system is getting images from 1000s of cameras placed in different parts of a city. Each camera is separated by 500 metres, clicks 10 frames per second and each frame is about 20 KB in size. There are services available to give vehicle details given vehicle no. There are different services available for image processing that can take in set of frames and return back the violation type and vehicles number plates that are in violation. Goal is to send the control room details regarding where violation occurred and vehicles involved and ability to trace back to the images. System must be scalable and fault tolerant as more cities can be added and more cameras can be added.
1. How will you store and manage the querying of the images what are your technology choices?2. In the case of speed violations you might need to combine images from one or more cameras as you cant achieve speed violation from a single camera.3. How will you prevent or handle out of order messages if any
Uber Product Design Interview Questions
- – San Andrés and Providence and
- Democratic Republic of Congo – All Cities
- – Baladiyat az¸ Z¸aayin
- Sao Tome and Principe – All Cities
- United Arab Emirates – All Cities
I applied through an employee referral I interviewed at Uber
Definitely takes forever to get back to you. I didn’t have the best experience. The company seems disorganized and felt a lack of communication throughout the process. I had my interview rescheduled many times by the recruiter.
I applied online. I interviewed at Uber
Typical interview process: screening HR call, portfolio presentation with a team panel.Recruiting call was positive. Steps well-coordinated, friendly conversation, shared tips and resources. Although at times, hearing back took a while.Team panel gave me a negative experience. One interviewer was friendly and listened. The other one was totally distracted by what was happening at home and was disengaged. I didn’t feel like he cared at all about the work or me as a person. I couldn’t picture working with him. Everything felt scripted and procedural. I dodged a bullet. I never heard back from them or the recruiter either. Terrible experience.
- Typical screening questions: why uber, why want to leave, what I look for in my next role, questions about my background.Typical portfolio questions: explain rationale, challenges, etc.
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How To Prepare For System Design Interviews
As you can see from the complex questions above, there is a lot of ground to cover when it comes to system design interview preparation. So its best to take a systematic approach to make the most of your practice time, and we recommend the three steps below.
For extra tips and resources, take a look at our system design interview prep guide and our list of 19 system design interview tips from ex-interviewers.
Design A Social Network And Message Board Service Like Quora Reddit Or Hackernews
For this question, youll design a forum-like system where users can post questions and links.
Other users can view and comment on the questions. Questions have tags that represent their topic and users can follow tags to see questions on specific topics. Users have a newsfeed that highlights popular questions from their followed tags and related topics.
Read Also: Erwin Data Modeler Interview Questions
Fault Tolerance And Replication
We will need server replicas in case the Driver Location or Notification servers die. A secondary server can take control when a primary server dies. We can also store data in persistent storage like solid state drives to provide fast input and output. We can quickly use this persistent storage to recover data in the event that both primary and secondary servers die.
How To Nail Your Next Tech Interview
In the fast-paced, ever-growing tech space, Uber has made a mark of its own. It’s not just a taxi service anymore it has expanded its services to food delivery, package delivery, and freight transportation as well. Uber is constantly on the lookout for good engineers â after all, itâs a tech company, and it heavily relies on new technologies to spread its reach.
Uber hires for software engineer, ML engineer, data engineer, technical program manager, and many more engineering positions. In this article, weâll look at what a typical tech interview process at Uber looks like, and other interesting information about the company:
Also Check: How To Be A Great Interviewer
Write Functional Code For Solving The Problem Given Below:
Return the result of a sequence of enqueue and dequeue actions without utilising a queue data structure. The following op are presented in the form of a linked list:
- A non-negative integer denotes “enqueue me.”
- -1 denotes either of the following:
- Dequeue the current root and append it to the result if the queue is not empty.
- Append -1 to the result if the queue is empty.
The end result should be returned as a linked list. As an auxiliary data structure, use two stacks. It is not permitted to use a queue.
C ++ code snippet which solves the given Data Structures and Algorithm problem is given below:
Node* makeAnswerList else return last }int dequeue // If the second stack is not empty, popping and returning from it. if == false) /* Otherwise we pop each and every element from the first stack and push into the second stack. */ while == false) // Lastly, we pop and return the root of the second stack. int value = stk2.top stk2.pop return value }Node* implementingQueue else } op = op-> link } return root }
In this question, we use two stacks to implement the queue data structure. As soon as a non-negative integer is found, we add it into the first stack and when we get a -1 in the input list, we perform the dequeue operation using the following criteria:
This way, the FIFO property of a queue is preserved and we get our required answer list.
Discuss The Core Features
So firstly divide the whole system into several core components and talk about some core features. If some other features your interviewer wants to include he/she will mention there. For now, we are going to consider the following features on Twitter
- The user should be able to tweet in just a few seconds.
- The user should be able to see Tweet Timeline
- Timeline: This can be divided into three parts
- User timeline: User sees his/her own tweets and tweets user retweet. Tweets that users see when they visit their profile.
- Home Timeline: This will display the tweets from people users follow.
- Search timeline: When users search some keywords or #tags and they see the tweets related to that particular keywords.
- The user should be able to follow another user.
- Users should be able to tweet millions of followers within a few seconds
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How Dispatch System Match The Riders To Drivers
- We have discussed that DISCO divides the map into tiny cells with a unique ID. This ID is used as a sharding key in DISCO. When supply receives the request from demand the location gets updated using the cell ID as a shard key. These tiny cells responsibilities will be divided into different servers lies in multiple regions . For example, we can allocate the responsibility of 12 tiny cells to 6 different servers lying in 6 different regions.
- Supply sends the request to the specific server based on the GPS location data. After that, the system draws the circle and filters out all the nearby cabs which meet the riders requirement.
- After that, the list of the cab is sent to the ETA to calculate the distance between the rider and the cab, not geographically but by the road system.
- The sorted ETA is then sent back to the supply system to offer to a driver.
If we need to handle the traffic for the newly added city then we can increase the number of servers and allocate the responsibilities of newly added cities cell IDs to these servers.
Uber Behavioral Interview Sample Questions
Behavioral interview questions are used to check if you would be a good cultural fit for the company. You can expect behavioral questions like:
For more behavioral interview questions.
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Design An Api Rate Limiter
Design service or tool that monitors the number of requests per window of time a service agrees to allow. If the number of requests exceeds the rate limit blocks all the excess calls.
Things to analyze and discuss:
- Limiting the number of requests an entity can send to an API within a time window, for example, twenty requests per second.
- Rate limiting should work for a distributed setup, as the APIs are available through a group of servers.
- How to handle throttling .
Approach For System Design Interviews + Uber/lyft Design
System Design interviews are subjective in nature, but if you follow the framework described below, you will avoid a lot of common pitfalls.
In the 2nd video, I walk through what that approach would look like in designing a cab hailing system like Uber/Lyft.
Uber/Lyft System Design
Design a taxi hailing service such as Uber/Lyft
Note: We are assuming that this is a general System Design Interview, which mostly involves backend design. If you are interviewing for a frontend-specific role, you will focus more on the UI.
Before reading this, please go through the following Section:
- Section: Anatomy of a Scalable Web Application
This question is very open-ended. Taxi-hailing apps can have any number of features. You want to distill the question down to 2-3 core features and design a system around those. Later on, you can always add more.
Make sure you talk to the interviewer while negotiating these features. Some interviewers might want a certain feature, or not care about another.
Ask them if it is ok to stick to these features and add more features later. While this is implicitly implied, it is good to call it out and get on the same page.
A good way of thinking about core features:
A ride-hailing service will be incomplete without being able to hail a ride and get in the cab.
Here is a list of features we can implement:
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