6.83. rebuildlistenentries()

Function Properties

Language: PLPGSQL

Return Type: integer

RebuildListenEntries() Invoked by various subscription and path modifying functions, this rewrites the sl_listen entries, adding in all the ones required to allow communications between nodes in the Slony-I cluster.

declare
	v_row	record;
begin
	-- First remove the entire configuration
	delete from sl_listen;

	-- Second populate the sl_listen configuration with a full
	-- network of all possible paths.
	insert into sl_listen
				(li_origin, li_provider, li_receiver)
			select pa_server, pa_server, pa_client from sl_path;
	while true loop
		insert into sl_listen
					(li_origin, li_provider, li_receiver)
			select distinct li_origin, pa_server, pa_client
				from sl_listen, sl_path
				where li_receiver = pa_server
				  and li_origin <> pa_client
			except
			select li_origin, li_provider, li_receiver
				from sl_listen;

		if not found then
			exit;
		end if;
	end loop;

	-- We now replace specific event-origin,receiver combinations
	-- with a configuration that tries to avoid events arriving at
	-- a node before the data provider actually has the data ready.

	-- Loop over every possible pair of receiver and event origin
	for v_row in select N1.no_id as receiver, N2.no_id as origin
			from sl_node as N1, sl_node as N2
			where N1.no_id <> N2.no_id
	loop
		-- 1st choice:
		-- If we use the event origin as a data provider for any
		-- set that originates on that very node, we are a direct
		-- subscriber to that origin and listen there only.
		if exists (select true from sl_set, sl_subscribe				, sl_node p		   		
				where set_origin = v_row.origin
				  and sub_set = set_id
				  and sub_provider = v_row.origin
				  and sub_receiver = v_row.receiver
				  and sub_active
				  and p.no_active
				  and p.no_id=sub_provider
				  )
		then
			delete from sl_listen
				where li_origin = v_row.origin
				  and li_receiver = v_row.receiver;
			insert into sl_listen (li_origin, li_provider, li_receiver)
				values (v_row.origin, v_row.origin, v_row.receiver);
			continue;
		end if;

		-- 2nd choice:
		-- If we are subscribed to any set originating on this
		-- event origin, we want to listen on all data providers
		-- we use for this origin. We are a cascaded subscriber
		-- for sets from this node.
		if exists (select true from sl_set, sl_subscribe
						where set_origin = v_row.origin
						  and sub_set = set_id
						  and sub_receiver = v_row.receiver
						  and sub_active)
		then
			delete from sl_listen
					where li_origin = v_row.origin
					  and li_receiver = v_row.receiver;
			insert into sl_listen (li_origin, li_provider, li_receiver)
					select distinct set_origin, sub_provider, v_row.receiver
						from sl_set, sl_subscribe
						where set_origin = v_row.origin
						  and sub_set = set_id
						  and sub_receiver = v_row.receiver
						  and sub_active;
			continue;
		end if;

	end loop ;

	return null ;
end ;