Class: QC::Database

Inherits:
Object
  • Object
show all
Defined in:
lib/queue_classic/database.rb

Constant Summary collapse

@@connection = 
nil

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(queue_name = nil) ⇒ Database

Returns a new instance of Database.



9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
 
# File 'lib/queue_classic/database.rb', line 9

def initialize(queue_name=nil)
  log("initialized")

  @top_boundary = (ENV["QC_TOP_BOUND"] || 9).to_i
  log("top_boundary=#{@top_boundary}")

  @table_name = queue_name || "queue_classic_jobs"
  log("table_name=#{@table_name}")

  @channel_name = @table_name
  log("channel_name=#{@channel_name}")

  db_url = (ENV["QC_DATABASE_URL"] || ENV["DATABASE_URL"])
  @db_params = URI.parse(db_url)
  log("uri=#{db_url}")
end

Instance Attribute Details

#table_name ⇒ Object (readonly)

Returns the value of attribute table_name.



6
7
8
 
# File 'lib/queue_classic/database.rb', line 6

def table_name
  @table_name
end

#top_boundary ⇒ Object (readonly)

Returns the value of attribute top_boundary.



7
8
9
 
# File 'lib/queue_classic/database.rb', line 7

def top_boundary
  @top_boundary
end

Instance Method Details

#connect ⇒ Object 



96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
 
# File 'lib/queue_classic/database.rb', line 96

def connect
  log("establishing connection")
  conn = PGconn.connect(
    @db_params.host,
    @db_params.port || 5432,
    nil, '', #opts, tty
    @db_params.path.gsub("/",""), # database name
    @db_params.user,
    @db_params.password
  )
  if conn.status != PGconn::CONNECTION_OK
    log("connection error=#{conn.error}")
  end
  conn
end

#connection ⇒ Object 



87
88
89
 
# File 'lib/queue_classic/database.rb', line 87

def connection
  @@connection ||= connect
end

#disconnect ⇒ Object 



91
92
93
94
 
# File 'lib/queue_classic/database.rb', line 91

def disconnect
  connection.finish
  @@connection = nil
end

#drain_notify ⇒ Object 



49
50
51
52
53
 
# File 'lib/queue_classic/database.rb', line 49

def drain_notify
  until connection.notifies.nil?
    log("draining notifications")
  end
end

#escape(string) ⇒ Object 



30
31
32
 
# File 'lib/queue_classic/database.rb', line 30

def escape(string)
  connection.escape(string)
end

#execute(sql, *params) ⇒ Object 



76
77
78
79
80
81
82
83
84
85
 
# File 'lib/queue_classic/database.rb', line 76

def execute(sql, *params)
  log("executing #{sql.inspect}, #{params.inspect}")
  begin
    params = nil if params.empty?
    connection.exec(sql, params)
  rescue PGError => e
    log("execute exception=#{e.inspect}")
    raise
  end
end

#listen ⇒ Object 



39
40
41
42
 
# File 'lib/queue_classic/database.rb', line 39

def listen
  log("LISTEN")
  execute("LISTEN #{@channel_name}")
end

#load_functions ⇒ Object 



112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
 
# File 'lib/queue_classic/database.rb', line 112

def load_functions
  execute(<<-EOD)
    -- We are declaring the return type to be queue_classic_jobs.
    -- This is ok since I am assuming that all of the users added queues will
    -- have identical columns to queue_classic_jobs.
    -- When QC supports queues with columns other than the default, we will have to change this.

    CREATE OR REPLACE FUNCTION lock_head(tname name, top_boundary integer) RETURNS SETOF queue_classic_jobs AS $$
    DECLARE
      unlocked integer;
      relative_top integer;
      job_count integer;
    BEGIN
      -- The purpose is to release contention for the first spot in the table.
      -- The select count(*) is going to slow down dequeue performance but allow
      -- for more workers. Would love to see some optimization here...

      EXECUTE 'SELECT count(*) FROM ' ||
        '(SELECT * FROM ' || quote_ident(tname) ||
        ' LIMIT ' || quote_literal(top_boundary) || ') limited'
        INTO job_count;

      SELECT TRUNC(random() * top_boundary + 1) INTO relative_top;
      IF job_count < top_boundary THEN
        relative_top = 0;
      END IF;

      LOOP
        BEGIN
          EXECUTE 'SELECT id FROM '
            || quote_ident(tname)
            || ' WHERE locked_at IS NULL'
            || ' ORDER BY id ASC'
            || ' LIMIT 1'
            || ' OFFSET ' || quote_literal(relative_top)
            || ' FOR UPDATE NOWAIT'
          INTO unlocked;
          EXIT;
        EXCEPTION
          WHEN lock_not_available THEN
            -- do nothing. loop again and hope we get a lock
        END;
      END LOOP;

      RETURN QUERY EXECUTE 'UPDATE '
        || quote_ident(tname)
        || ' SET locked_at = (CURRENT_TIMESTAMP)'
        || ' WHERE id = $1'
        || ' AND locked_at is NULL'
        || ' RETURNING *'
      USING unlocked;

      RETURN;
    END;
    $$ LANGUAGE plpgsql;

    CREATE OR REPLACE FUNCTION lock_head(tname varchar) RETURNS SETOF queue_classic_jobs AS $$
    BEGIN
      RETURN QUERY EXECUTE 'SELECT * FROM lock_head($1,10)' USING tname;
    END;
    $$ LANGUAGE plpgsql;
 EOD
end

#log(msg) ⇒ Object 



183
184
185
 
# File 'lib/queue_classic/database.rb', line 183

def log(msg)
  Logger.puts(["database", msg].join(" "))
end

#notify ⇒ Object 



34
35
36
37
 
# File 'lib/queue_classic/database.rb', line 34

def notify
  log("NOTIFY")
  execute("NOTIFY #{@channel_name}")
end

#set_application_name ⇒ Object 



26
27
28
 
# File 'lib/queue_classic/database.rb', line 26

def set_application_name
  execute("SET application_name = 'queue_classic'")
end

#transaction ⇒ Object 



61
62
63
64
65
66
67
68
69
70
 
# File 'lib/queue_classic/database.rb', line 61

def transaction
  begin
    execute 'BEGIN'
    yield
    execute 'COMMIT'
  rescue Exception
    execute 'ROLLBACK'
    raise
  end
end

#transaction_idle? ⇒ Boolean

Returns:

  • (Boolean) 


72
73
74
 
# File 'lib/queue_classic/database.rb', line 72

def transaction_idle?
  connection.transaction_status == PGconn::PQTRANS_IDLE
end

#unlisten ⇒ Object 



44
45
46
47
 
# File 'lib/queue_classic/database.rb', line 44

def unlisten
  log("UNLISTEN")
  execute("UNLISTEN #{@channel_name}")
end

#unload_functions ⇒ Object 



176
177
178
179
180
181
 
# File 'lib/queue_classic/database.rb', line 176

def unload_functions
  execute(<<-EOD)
    DROP FUNCTION IF EXISTS lock_head(tname varchar);
    DROP FUNCTION IF EXISTS lock_head(tname name, top_boundary integer);
  EOD
end

#wait_for_notify(t) ⇒ Object 



55
56
57
58
59
 
# File 'lib/queue_classic/database.rb', line 55

def wait_for_notify(t)
  log("waiting for notify timeout=#{t}")
  connection.wait_for_notify(t) {|event, pid, msg| log("received notification #{event}")}
  log("done waiting for notify")
end