Concurrent requests to ruby REST API not possible - mysql

Question

I am trying to create some small REST API using ruby with Sinatra gem running on thin server. The point is to get an idea about how easy/hard is to build such REST API consisting of micro web services and to compare this with other programming languages / technologies available at Amazon's AWS. I have created one quite easily, here's the code (just minimal working project, not yet considering any kind of optimization):
require 'sinatra'
require 'mysql'
require 'json'
set :environment, :development
db_host = 'HOST_URL'
db_user = 'USER'
db_pass = 'PASSWORD'
db_name = 'DB_NAME'
db_enc = 'utf8'
select = 'SELECT * FROM table1 LIMIT 30'
db = Mysql.init
db.options Mysql::SET_CHARSET_NAME, db_enc
db = db.real_connect db_host, db_user, db_pass, db_name
get '/brands' do
rs = db.query select
#db.close
result = []
rs.each_hash do |row|
result.push row
end
result.to_json
end
Running this with ruby my_ws.rb starts Sinatra running on thin, no problem.
Using curl from my terminal like curl --get localhost:4567/brands is also not a problem returning the desired JSON response.
The real problem I am tackling now for few hours already (and searching on Google of course, reading lot of resources also here on SO) is when I try to benchmark the micro WS using Siege with more concurrent users:
sudo siege -b http://localhost:4567/brands -c2 -r2
This should run in benchnark mode issuing 2 concurrent request (-c2 switch) 2 times (-r2 switch). In this case I always get an error in the console stating Mysql::ProtocolError - invalid packet: sequence number mismatch(102 != 2(expected)): while the number 102 is always different on each run. If I run the benchmark only for one user (one concurrent request, i.e. no concurrency at all) I can run it even 1000 times with no errors (sudo siege -b http://localhost:4567/brands -c1 -r1000).
I tried adding manual threading into my code like:
get '/brands' do
th = Thread.new do
rs = db.query select
#db.close
result = []
rs.each_hash do |row|
result.push row
end
result.to_json
end
th.join
th.value
end
but with no help.
From what I have found:
Sinatra is multithreaded by default
thin is also multithreaded if run from Sinatra if run by ruby script.rb
multithreading seems to have no effect on DB queries - here it looks like no concurrency is possible
I'm using ruby-mysql gem as I have found out it's newer then (just) mysql gem but in the end have no idea which one to use (found old articles to use mysql and some other to use ruby-mysql instead).
Any idea on how to run concurrent requests to my REST API? I need to benchmark and compare it with other languages (PHP, Python, Scala, ...).

Answer 1

The problem is solved with two fixes.
The first one is by replacing the mysql adapter with mysql2.
The second one was the real cause of the problem: the MySQL connection was created once for runtime before the I could even dive into the thread (i.e. before the code for route was executed) causing (logically) connection locks.
Now with mysql2 and connection to DB moved under the route execution it is all working perfectly fine even for 250 concurrent requests! The final code:
require 'sinatra'
require 'mysql2'
require 'json'
set :environment, :development
db_host = 'HOST_URL'
db_user = 'USER'
db_pass = 'PASSWORD'
db_name = 'DB_NAME'
db_enc = 'utf8'
select = 'SELECT * FROM table1 LIMIT 30'
get '/brands' do
result = []
Mysql2::Client.new(:host => db_host, :username => db_user, :password => db_pass, :database => db_name, :encoding => db_enc).query(select).each do |row|
result.push row
end
result.to_json
end
Running sudo siege -b http://localhost:4567/brands -c250 -r4 gives me now:
Transactions: 1000 hits
Availability: 100.00 %
Elapsed time: 1.54 secs
Data transferred: 2.40 MB
Response time: 0.27 secs
Transaction rate: 649.35 trans/sec
Throughput: 1.56 MB/sec
Concurrency: 175.15
Successful transactions: 1000
Failed transactions: 0
Longest transaction: 1.23
Shortest transaction: 0.03