davetapley

[4] pry(main)> User.all.second
  User Load (42.5ms)  SELECT "users".* FROM "users" WHERE "users"."deleted_at" IS NULL
=> #<User id: 2, ...>

[5] pry(main)> User.all.offset(1).limit(1)
  User Load (0.5ms)  SELECT "users".* FROM "users" WHERE "users"."deleted_at" IS NULL LIMIT 1 OFFSET 1
=> [#<User id: 2, ...]

davetapley

{
name: "error",
length: 97,
severity: "ERROR",
code: "42P01",
position: "13",
file: "parse_relation.c",
line: "873",
routine: "parserOpenTable"
}

davetapley

$ ab -n 1000 -c 1000 http://localhost:3000/hang
This is ApacheBench, Version 2.3 <$Revision: 1554214 $>
Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/
Licensed to The Apache Software Foundation, http://www.apache.org/

Benchmarking localhost (be patient)
apr_socket_recv: Connection reset by peer (104)

davetapley

test=# CREATE TABLE tzs(with_tz TIMESTAMP WITH TIME ZONE, without_tz TIMESTAMP WITHOUT TIME ZONE, comment TEXT);                                                                                                     
CREATE TABLE
test=# INSERT INTO tzs VALUES( now(), now(), 'now()');
test=# INSERT INTO tzs VALUES( timezone('America/New_York', now()), timezone('America/New_York', now()), 'timezone(New York, now())');                                                                               
INSERT 0 1
test=# INSERT INTO tzs VALUES( '2014-05-06T17:14:00Z', '2014-05-06T17:14:00Z', 'ISO 8601 Zulu' );                                                                                                                    
INSERT 0 1
test=# INSERT INTO tzs VALUES( '2014-05-06T17:14:00-04:00', '2014-05-06T17:14:00-04:00', 'ISO 8601 offset' );                                                                                                        
INSERT 0 1
test=# SELECT * FROM tzs ;

davetapley

class ArrayIter < Array

  class Iter < SimpleDelegator
    attr_reader :next
    attr_reader :prev
  end

  def <<(other)
    last.instance_variable_set(:@next, other) if last
    other_iter = Iter.new other

davetapley

Start with a list of clusters:
a, b, x, c, x, x, d, e, f, g, x, h

Select out clusters to try and find a place for:

a, b, c, d, e, f, g, h

Map over a method to (optionally) assign a place (pN) to each cluster:
(this is done with a DelegateClass containing the place or nil)

davetapley

Two tables share a user_id, a tstzrange called period, then each have another column called category and place_id respectively. Both have constraints allowing a user to only have one 'other column' value at any time:

 user_id    | integer                  | not null
 period     | tstzrange                | not null
 category   | character varying(16)    |

    "category_events_user_id_period_excl" EXCLUDE USING gist (user_id WITH =, period WITH &&)

davetapley

test=# SELECT isempty('[0,0]' :: int4range);
 isempty 
---------
 f
(1 row)

test=# SELECT isempty('[0,0)' :: int4range);
 isempty 
---------
 t

davetapley

   "events_pkey" PRIMARY KEY, btree (user_id, period)
   "events_user_id_period_excl" EXCLUDE USING gist (user_id WITH =, period WITH &&)

davetapley

  def self.included(o)
    o.extend ClassMethods

    o.set_primary_key [:user_id, :period]
    o.unrestrict_primary_key
  end