ruby script to calculate primes

I have a friend who is really into Pi. In fact he claims to have the first 200 digits memorized.Me I think primes are way cooler, first of all there are a lot of them, and they occur more than you think.

For instance 2,000,000,000,003 is a prime number!

Anyway below is a script I wrote which can be used to determine is a number is a prime or you can just run it and it will start printing out all of the primes starting with the number 2.

ruby primes.rb -h  Usage: primes.rb [ -c ] or [ -o integer]  -c                               calculate primes  -o, --one_integer integer        check if one integer is a prime  -h                               Display this screen  example: primes -c calculate all primes starting with the number 2  example: primes -o check if a given integer is a prime

The code:

require 'optparse'  require 'rubygems'  ###########  # methods #  ###########  def primes(start)    foo = 2    out = Array.new    root = Math.sqrt(start)    div = root.to_i    while  foo <=  div      foo = foo + 1      ans = start.to_f / foo.to_f      nu,de = ans.to_s.split('.')      if de == "0"        out.push(de)      end    end  return out  end  ##################  # define options #  ##################  options = {}  optparse = OptionParser.new do|opts|     opts.banner = "Usage: primes.rb [ -c ] or [ -o integer]"     options[:calculate_primes] = false     opts.on( '-c', 'calculate primes' ) do        options[:calculate_primes] = true     end    options[:one_integer] = nil      opts.on( '-o integer', '--one_integer integer', "check if one integer       is a prime" ) do |check_this|        options[:one_integer] = check_this     end     opts.on( '-h', 'Display this screen' ) do        puts opts        puts "example: primes -c calculate all primes starting with the number 2"        puts "example: primes -o check if a given integer is a prime"        exit     end   optlength = ARGV.length     if optlength < 1        puts opts.banner        exit     end  end  optparse.parse!  if options[:calculate_primes]    start = 2    while start > 1      start = start +1      if start.odd?       out = primes(start)       count = out.count         if count == 0           puts start.to_s         end      end    end  end  if options[:one_integer]    check_this = "#{options[:one_integer]}"    if check_this.to_i.even?      puts check_this.to_s + " is not a prime number"      exit    end    out = primes(check_this)      count = out.count      if count == 0        puts check_this.to_s + " is a prime number"      else        puts check_this.to_s + " is not a prime number"      end  end

Update:Turns out Ruby has a built in function to do this in 3 lines.

require 'mathn'  list_primes = Prime.new  puts list_primes.each { |prime| print prime.to_s + "n", " "; break unless prime > 1 }

Thank you mathn!

lessons learn while devops@posterous

I’m a proud former employee of Posterous and worked there for the 10 months prior to the twitter acquisition.
Although it was a short time  we experienced a lot of growth and it was very intense with a lot of changes in user behavior, product and infrastructure.
Like everything in life when you look back you can always find better ways to do things.
Its been about six months since I left and below are a few of the lessons that I’ve learned and will take with me to my next gig.

MySQL:

– Install a gui tool to help manage the DB’s. Yeah gui’s sound lame but they put a lot of valuable information together in one place and don’t cost you anything.

– Always have a spare slave that you can use to test out new configs, place in service for a while, iterate.

– Go to every MySQL meet up possible, they are a huge source of information and you will walk away from everyone with one or more new trick up your sleeve.

FIGHT SPRAWL:

– Every time you introduce a new technology make it a requirement to have it replace an existing technology in addition to supporting a new feature.
In most cases this isn’t a stretch as a lot of technologies are similar to each other (redis/memcached), (riak/mongodb) etc……

ADMIT YOUR SHORT COMINGS, FOCUS ON THE POSITIVE:

Posterous was rails shop with an abundance of really skilled developers which meant we moved at a rapid pace, multiple deployments a day….we were constantly in a state of change.
Working in an environment like that has advantages and disadvantages.
The disadvantages are that change equals risk.
Advantages are that we were able to push changes to the site soon after the code change, which means if something when wrong the developer didn’t have to context switch to fix the problem.
We spent a lot of time addressing the negative side of rapid development by attempting to introduce a QA process meant to slow things down and prevent mistakes.
Now that I look back I think we should have focused on the positive side of rapid change by speeding up the deployment process and pushing code even more often.
In a perfect world you have a automated QA test that runs in 1 minute and has a 100% coverage….or maybe thats not the perfect world but fantasy island I’m thinking of.

FORCE YOURSELF TO PLAN LONG:

In a rapidly moving start-up with a burn rate it seems like a waste of time to plan long but when it comes to infrastructure its absolutely necessary.
I can go to most web companies and when they talk about their infrastructure there are always one off services that they considered “legacy”.
Legacy is code word for we rolled it out without thinking more than a month out.
Once a month take the key people offsite for a few hours to white board your current infrastructure and what it would look like you got to design it from scratch….that is your long term plan. Now when choosing a new technology you already know how it will fit in long term.

MySQL replication and failover with tungsten-replicator

Having administered MySQL in production for the last 7 years I know how painful it is when a master goes down or when replication breaks.Its also annoying when you rebuild a slave and it takes a really long time for replication to catch up.I decided to give tungsten-replication a look as it claims to be high performance and handles promoting a slave to master.

My setup:

—Two rackspace cloud servers running Ubuntu 12.04

—2GB RAM

—4 cores

—Percona server 5.5

—tungsten-replicator 2.0.5 (free version)

Installation

It took me a while( ~4 hours) to satisfy all of the prerequisites for the OS and MySQL.This wasn’t helped by the mostly horrible documentation. All of the information was there but it was laid out all over the place and took several attempts to find all the pieces.It would have been a huge help to have a script that you can run to check your prerequisites such as ruby version, java version etc….Once I satisfied all the prerequisites it was time to move on to the config

Configuration

The good news here is that tungsten-replication comes with a scripted installation designed to install and configure all of your nodes with one command.The bad news once again is that the documentation is scattered all over the place and really incomplete.Also a really annoying problem is getting to the help output with the commands.Some require —help, some help and others have nothing at all.In the open source version there are 2 types of configuration.1. master-slave2. direct which supports multi-master

master-slave

To get master slave up I downloaded the release:

wget http://code.google.com/p/tungsten-replicator/downloads/detail?name=tungsten-replicator-2.0.5.tar.gz&can=2&q=

untarred it:

tar xzvf tungsten-replicator-2.0.5.tar.gz

cd to tungsten-replicator-2.0.5 and ran the following command:

./tools/tungsten-installer -v       --master-slave       --master-host=198.201.208.173       --datasource-user=tungsten       --datasource-password=tungsten       --datasource-mysql-conf=/etc/mysql/my.cnf       --service-name=gabriel       --home-directory=/opt/tungsten       --cluster-hosts=198.201.208.173,198.201.206.221       --start-and-report

This should install tungsten-replicator to /opt/tungsten start the service on both nodes and report back with its status.To check create a database on the master, it should show up on the slave.

Replication Performance

Now that I have my master-slave up and running I decided to test the replication speed.I took a 40MB dump file and loaded it onto the master.It took 6 seconds to load.What surprised me was how long it took to complete the load on the slave.It took 43 seconds for the slave to get the complete dump, that was 43 seconds after the master load completed.To eliminate the network as a bottle neck I scp’d the file from master to slave and that took 6 seconds.My guess is the process on the master that reformates the statements with global id’s is really inefficient.

failover

I still haven’t figured out how to automatically failover( good luck looking in the docs), but I did figure out how to manually promote the slave to master.First thing you need to do it take replication offline, that doesn’t mean stopping the daemon but just pausing the replication process:

/opt/tungsten/tungsten/tungsten-replicator/bin/trepctl -service gabriel offline

This needs to be run on both hosts.

To verify that both hosts have replication offline run the following:

/opt/tungsten/tungsten/tungsten-replicator/bin/trepctl status

Now your ready, in my environment 198.201.208.173 is the current master and 198.201.206.221 the slave( you can see this in the output of the status command).The first step is to change the master to a slave:

/opt/tungsten/tungsten/tungsten-replicator/bin/trepctl -service gabriel setrole  -role slave -uri thl://198.201.206.221/

run that on the current master

Then turn the old slave on to a master:/opt/tungsten/tungsten/tungsten-replicator/bin/trepctl -service gabriel setrole -role master -uri thl://198.201.206.221/Run this on the current slave.

Now check your work with the status command.When it looks good run this command on both hosts:

/opt/tungsten/tungsten/tungsten-replicator/bin/trepctl -service gabriel online

Again check your work with the status command.

protip

To run commands on both hosts is easy as in the host setup process you copied over ssh keys and authorized_keys files.I just used a bash for loop:

for H in 198.201.208.173 198.201.206.221;  do ssh root@$H "/root/tungsten-replicator-2.0.5/tungsten-replicator/bin/trepctl status"; done

conclusion

Given the replication lag, poor documentation, long setup, and the fact that its really early I consider tungsten-replicator to have a lot of potential but mostly a science experiment for now.Of course this is with the free version.Like I said in the beginning I know how much it sucks when a master fails of when replication breaks.Tungsten-replicator has all of the features needed to solve all of these problems it just doesn’t give me enough confidence to run this in my production environment…..yet