Module: PgVersions

Defined in:
lib/pg_versions/pg_versions.rb,
lib/pg_versions.rb,
lib/pg_versions/rails.rb,
lib/pg_versions/version.rb

Overview

TODO: prepared statements?

Defined Under Namespace

Classes: Connection, ConnectionAcquisitionFailedError, Engine, Notification

Constant Summary collapse

VERSION = 
"1.0"

Class Method Summary collapse

Class Method Details

.bump(*channels, connection: nil) ⇒ Object

TODO: ensure this is called only once per transaction, or that all bumps occur in the same order in all transactions, to avoid deadlocks



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# File 'lib/pg_versions/pg_versions.rb', line 77

def self.bump(*channels, connection: nil)
	PgVersions.with_connection(connection) { |pg_connection|
		channels = [channels].flatten.sort
		return {} if channels.size == 0
		quoted_channels = channels.map.with_index { |channel, i| "(#{i},'#{pg_connection.escape_string(channel)}')" }.join(", ")
		# table-wide share lock is there to mutually exclude table cleaner
		# clock_timestamp() - this has to be a timestamp after table lock got acquired
		pg_connection.exec("
			LOCK TABLE pg_versions IN ACCESS SHARE MODE;
			WITH 
				to_bump(i, channel) AS (VALUES #{quoted_channels})
				, current_instant(ts) AS (VALUES (clock_timestamp()))
				, updated AS (
						INSERT INTO pg_versions(channel, instant, counter)
						SELECT to_bump.channel, (SELECT ts FROM current_instant), 0 FROM to_bump
						ON CONFLICT (channel) DO UPDATE SET
							instant = GREATEST(pg_versions.instant, EXCLUDED.instant),
							counter = CASE WHEN pg_versions.instant < EXCLUDED.instant THEN 0 ELSE pg_versions.counter + 1 END
						RETURNING channel, instant, pg_versions.counter
						)
			SELECT DISTINCT
				i
				, #{timestamp_to_integers('updated.instant')} || ',' || updated.counter::text AS version
				, pg_notify(updated.channel::text, #{timestamp_to_integers('updated.instant')} || ',' || updated.counter::text)::text
			FROM
				to_bump
				JOIN updated ON to_bump.channel = updated.channel;
		").map { |row| [channels[Integer(row["i"])], string_to_version(row["version"])] }.to_h
	}
end

.create_table(connection = nil) ⇒ Object 



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# File 'lib/pg_versions/pg_versions.rb', line 60

def self.create_table(connection=nil)
	PgVersions.with_connection(connection) { |pg_connection|
		open(File.dirname(__FILE__)+"/../../create-table.sql") { |sql_file|
			pg_connection.exec sql_file.read
		}
	}
end

.drop_table(connection = nil) ⇒ Object 



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# File 'lib/pg_versions/pg_versions.rb', line 68

def self.drop_table(connection=nil)
	PgVersions.with_connection(connection) { |pg_connection|
		open(File.dirname(__FILE__)+"/../../drop-table.sql") { |sql_file|
			pg_connection.exec sql_file.read
		}
	}
end

.read(*channels, connection: nil) ⇒ Object 



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# File 'lib/pg_versions/pg_versions.rb', line 109

def self.read(*channels, connection: nil)
	PgVersions.with_connection(connection) { |pg_connection|
		channels = [channels].flatten.sort
		return {} if channels.size == 0
		versions = {}
		quoted_channels = channels.map.with_index { |channel, i| "(#{i},'#{pg_connection.escape_string(channel)}')" }.join(", ")
		not_found_channels = pg_connection.exec("
			LOCK TABLE pg_versions IN ACCESS SHARE MODE;
			WITH
				channels(i, channel) AS (VALUES #{quoted_channels})
			SELECT
				i
				, #{timestamp_to_integers('instant')} || ',' || counter AS version
			FROM
				channels
				JOIN pg_versions ON pg_versions.channel = channels.channel
			ORDER BY
				i DESC;
		").each { |row|
			versions[channels.delete_at(Integer(row["i"]))] = string_to_version(row["version"])
		}
		#TODO: bump in the same query instead of calling bump
		versions.merge!(self.bump(channels, connection: pg_connection))  if channels.size > 0
		versions
	}
end

.string_to_version(version_str) ⇒ Object 



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# File 'lib/pg_versions/pg_versions.rb', line 55

def self.string_to_version(version_str) 
	version_str.split(",").map { |str| Integer(str) }
end

.timestamp_to_integers(input) ⇒ Object 



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# File 'lib/pg_versions/pg_versions.rb', line 37

def self.timestamp_to_integers(input)
	"to_char(%s, 'YYYYMMDD')::integer || ',' || to_char(%s, 'HH24MISS')::integer || ',' || to_char(%s, 'US')::integer"%[input, input, input]
end

.with_connection(pg_connection) ⇒ Object 



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# File 'lib/pg_versions/pg_versions.rb', line 42

def self.with_connection(pg_connection)
	if pg_connection
		yield pg_connection
	elsif defined? ActiveRecord
		ActiveRecord::Base.connection_pool.with_connection { |ar_connection|
			yield ar_connection.instance_variable_get(:@connection)
		}
	else
		raise ConnectionAcquisitionFailedError, "Missing connection. Either pass pg connection object or import ActiveRecord."
	end
end