Selecting database for building highly scalable and available URL shortner service

We want to build a URL shortening service.

Design goals :

a) Scalable

b) Highly available

I was analysing which type and specifically which database to use for the purpose.

a) Relational DB : Rejected

- Data is not relational   - SQL DB with ACID compliance is hard to scale  

b) Graph DB : Rejected

- Data model is not inherently graphical  

c) Persistent Key-value store : An option

- Most of the DB queries would be around slug   - It is faster to read from a key-value store due to limited   - Analytics will be taken care of separately   - The clustered mode will be easy to scale 

d) Document Store : An option

- Scalable   - Queries from various fields of a document are supported   - Data is not nested  

Based on the mentioned points, persistent Key-value store should be the best option for the same.

Can someone please help me out, if I missed anything in the consideration or if I may be wrong here. It would be of help.

If a persistent key-value store is best available option, then what is the correct way to select amongst the available options (REDIS, Couchbase, Aerospike, etc)

How to handle java8 installation issue when building h2o docker image [using Dockerfile in the repository]

I’m trying to build an H2o docker image, using https://github.com/h2oai/h2o-3/blob/master/Dockerfile.

It gets the following error:

E: Package ‘oracle-java8-installer’ has no installation candidate

The command ‘/bin/sh -c echo ‘DPkg::Post-Invoke {“/bin/rm -f /var/cache/apt/archives/.deb || true”;};’ | tee /etc/apt/apt.conf.d/no-cache && echo “deb http://mirror.math.princeton.edu/pub/ubuntu xenial main universe” >> /etc/apt/sources.list && apt-get update -q -y && apt-get dist-upgrade -y && apt-get clean && rm -rf /var/cache/apt/ && DEBIAN_FRONTEND=noninteractive apt-get install -y wget unzip python-pip python-sklearn python-pandas python-numpy python-matplotlib software-properties-common python-software-properties && add-apt-repository -y ppa:webupd8team/java && apt-get update -q && echo debconf shared/accepted-oracle-license-v1-1 select true | debconf-set-selections && echo debconf shared/accepted-oracle-license-v1-1 seen true | debconf-set-selections && DEBIAN_FRONTEND=noninteractive apt-get install -y oracle-java8-installer && apt-get clean && wget http://h2o-release.s3.amazonaws.com/h2o/latest_stable -O latest && wget –no-check-certificate -i latest -O /opt/h2o.zip && unzip -d /opt /opt/h2o.zip && rm /opt/h2o.zip && cd /opt && cd find . -name 'h2o.jar' | sed 's/.\///;s/\/h2o.jar//g' && cp h2o.jar /opt && /usr/bin/pip install find . -name "*.whl" && cd / && wget https://raw.githubusercontent.com/h2oai/h2o-3/master/docker/start-h2o-docker.sh && chmod +x start-h2o-docker.sh && wget http://s3.amazonaws.com/h2o-training/mnist/train.csv.gz && gunzip train.csv.gz && wget https://raw.githubusercontent.com/laurendiperna/Churn_Scripts/master/Extraction_Script.py && wget https://raw.githubusercontent.com/laurendiperna/Churn_Scripts/master/Transformation_Script.py && wget https://raw.githubusercontent.com/laurendiperna/Churn_Scripts/master/Modeling_Script.py’ returned a non-zero code: 100

I’m assuming it may be related to the recent Oracle JDK License Update.

Is there a way to resolve this error in building the docker image?

Building complex sentences based on a data structure

I really do not like how bad this looks. It is not readable and I am not sure if I need the stacked map’s. There are a lot of iterations going on here (map, join, replace) and performance is really important, please help 🙁

Input:

const alternatives = [   "flex",   "float",   [     "background-size",     "background-image"   ] ] 

Expected Output:

'Consider using 'flex', 'float' or 'background-size' with 'background-image' instead.' 

Working Code:

const result = `Consider using $  {alternatives                  .map((alternative) => {                    return Array.isArray(alternative)                      ? alternative.map((a) => `'$  {a}'`).join(' with ')                      : `'$  {alternative}'`;                  })                  .join(', ')                  .replace(/, ([^,]*)$  /, ' or $  1')} instead.` 

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Find busiest period in building

The task

You are given a list of data entries that represent entries and exits of groups of people into a building. An entry looks like this:

{“timestamp”: 1526579928, count: 3, “type”: “enter”}

This means 3 people entered the building. An exit looks like this:

{“timestamp”: 1526580382, count: 2, “type”: “exit”}

This means that 2 people exited the building. timestamp is in Unix time.

Find the busiest period in the building, that is, the time with the most people in the building. Return it as a pair of (start, end) timestamps. You can assume the building always starts off and ends up empty, i.e. with 0 people inside.

const stamp = [   {"timestamp": 1526579928, count: 3, "type": "enter"},   {"timestamp": 1526580382, count: 2, "type": "exit"},   {"timestamp": 1526579938, count: 6, "type": "enter"},   {"timestamp": 1526579943, count: 1, "type": "enter"},   {"timestamp": 1526579944, count: 0, "type": "enter"},   {"timestamp": 1526580345, count: 5, "type": "exit"},   {"timestamp": 1526580351, count: 3, "type": "exit"}, ]; 

My imperative solution:

const findBusiestPeriod = lst => {   let visitors = 0;   const busiestPeriod = {     start: null,     end: null,     maxVisitors: null,   };    lst.forEach((v, i) => {     visitors = v.type === "enter" ?       visitors + v.count :       visitors - v.count;      if (visitors > busiestPeriod.maxVisitors) {       busiestPeriod.maxVisitors = visitors;       busiestPeriod.start = v.timestamp;       busiestPeriod.end = lst[i + 1].timestamp;     } else if (visitors === busiestPeriod.maxVisitors){       busiestPeriod.end = lst[i + 1].timestamp;     }   });   return [busiestPeriod.start, busiestPeriod.end]; };  console.log(findBusiestPeriod(stamp)); 

My functional solution

const findBusiestPeriod2 = lst => {   const {start, end} = lst.reduce((busiestPeriod, v, i) => {     busiestPeriod.visitors = v.type === "enter" ?       busiestPeriod.visitors + v.count :       busiestPeriod.visitors - v.count;     const visitors = busiestPeriod.visitors;     if (!busiestPeriod.maxVisitors || visitors > busiestPeriod.maxVisitors) {       busiestPeriod.maxVisitors = visitors;       busiestPeriod.start = v.timestamp;       busiestPeriod.end = lst[i + 1].timestamp;     } else if (visitors === busiestPeriod.maxVisitors){       busiestPeriod.end = lst[i + 1].timestamp;     }     return busiestPeriod;   }, {visitors: 0, maxVisitor: null,});   return [start, end]; };  console.log(findBusiestPeriod2(stamp));