How can I build a front end for querying a Redshift database (hopefully with Rails)

activerecord, amazon-redshift, amazon-web-services, ruby-on-rails

Solution

#app/models/data_warehouse.rb
class DataWarehouse < ActiveRecord::Base                      
  establish_connection "redshift_staging"
  #or, if you want to have a db per environment
  #establish_connection "redshift_#{Rails.env}"
end

Note that we are connecting on 5439, not the default 5432 so I specify the port Also, I specify a schema, beta, which is what we use for our unstable aggregates, you could either have a different db per environment as mentioned above, or use various schemas and include them in the search path for ActiveRecord

#config/database.yml
redshift_staging:                                                          
  adapter: postgresql                                                      
  encoding: utf8                                                           
  database: db03                                                         
  port: 5439                                                               
  pool: 5                                                                  
  schema_search_path: 'beta'                                                                                          
  username: admin                                                        
  password: supersecretpassword                                               
  host: db03.myremotehost.us  #your remote host here, might be an aws url from Redshift admin console 

###OPTION 2, a direct PG Connection

  class DataWarehouse < ActiveRecord::Base                      

    attr_accessor :conn                                                       

    def initialize                                                            
      @conn = PG.connect(                                                     
       database: 'db03',                                                   
       port: 5439,                                                           
       pool: 5,                                                              
       schema_search_path: 'beta',                                           
       username: 'admin',                                                  
       password: 'supersecretpassword',                                         
       host: 'db03.myremotehost.us'                                               
      )                                                                       
    end    
  end


[DEV] main:0> redshift = DataWarehouse
E, [2014-07-17T11:09:17.758957 #44535] ERROR -- : PG::InsufficientPrivilege: ERROR:  permission denied to set parameter "client_min_messages" to "notice" : SET client_min_messages TO 'notice'
(pry) output error: #<ActiveRecord::StatementInvalid: PG::InsufficientPrivilege: ERROR:  permission denied to set parameter "client_min_messages" to "notice" : SET client_min_messages TO 'notice'>   

UPDATE:

I ended up going with option 1, but using this adapter for now for multiple reasons:

https://github.com/fiksu/activerecord-redshift-adapter

Reason 1: ActiveRecord postgresql adapter sets client_min_messages Reason 2: adapter also attempts to set Time Zone, which redshift doesn't allow (http://docs.aws.amazon.com/redshift/latest/dg/c_redshift-and-postgres-sql.html) Reason 3: Even if you change the code in ActiveRecord for the first two errors, you run into additional errors that complain that Redshift is using Postgresql 8.0, at that point I moved on to the adapter, will revisit and update if I find something better later.

I renamed my table to base_aggregate_redshift_tests (notice plural) so ActiveRecord was easily able to connect, if you can't change your table names in redshift use the set_table method I have commented out below

#Gemfile:
gem 'activerecord4-redshift-adapter', github: 'aamine/activerecord4-redshift-adapter'

Option 1

#config/database.yml
redshift_staging:                                                                                                             
  adapter: redshift                                                                                                           
  encoding: utf8                                                                                                              
  database: db03                                                                                                           
  port: 5439                                                                                                                  
  pool: 5                                                                                                                     
  username: admin                                                                                                
  password: supersecretpassword                                                                                                  
  host: db03.myremotehost.us                                                                                                       
  timeout: 5000   

#app/models/base_aggregates_redshift_test.rb
#Model named to match my tables in Redshift, if you want you can set_table like I have commented out below

class BaseAggregatesRedshiftTest < ActiveRecord::Base
  establish_connection "redshift_staging"
  self.table_name = "beta.base_aggregates_v2"
end

in console using self.table_name -- notice it queries the right table, so you can name your models whatever you want

[DEV] main:0> redshift = BaseAggregatesRedshiftTest.first                                                                    
D, [2014-07-17T15:31:58.678103 #43776] DEBUG -- :   BaseAggregatesRedshiftTest Load (45.6ms)  SELECT "beta"."base_aggregates_v2".* FROM "beta"."base_aggregates_v2" LIMIT 1            

Option 2

#app/models/base_aggregates_redshift_test.rb
class BaseAggregatesRedshiftTest < ActiveRecord::Base
  set_table "beta.base_aggregates_v2"

  ActiveRecord::Base.establish_connection(
    adapter: 'redshift',
    encoding: 'utf8',
    database: 'staging',
    port: '5439',
    pool: '5',
    username: 'admin',
    password: 'supersecretpassword',
    search_schema: 'beta',
    host: 'db03.myremotehost.us',
    timeout: '5000'
  )

end

#in console, abbreviated example of first record, now it's using the new name for my redshift table, just assuming I've got the record at base_aggregates_redshift_tests because I didn't set the table_name

[DEV] main:0> redshift = BaseAggregatesRedshiftTest.first
D, [2014-07-17T15:09:39.388918 #11537] DEBUG -- :   BaseAggregatesRedshiftTest Load (45.3ms)  SELECT "base_aggregates_redshift_tests".* FROM "base_aggregates_redshift_tests" LIMIT 1
#<BaseAggregatesRedshiftTest:0x007fd8c4a12580> {
                                                :truncated_month => Thu, 31 Jan 2013 19:00:00 EST -05:00,
                                                :dma => "Cityville",
                                                :group_id => 9712338,
                                                :dma_id => 9999 
                                                }

Good luck @johncorser!

Problem

Original source