Make more simple incremental update (#944)

Replacing update on the whole table with an update only on changed rows.

The goal is to update more quickly by just updating the changing content.
The update now focus on osm_id of changed rows, it use index. Add a where clause tags != update_tags(tags, geometry) en ensure only update when changed.

It requires one more trigger and a table to store changed osm_id.

The UPDATE is keep in a function to be reusable for initial setup and trigger update.

I try many code layout before done it in this way with the goal to keep the code for initial pass and for update. It should have low impact on initial data load. Better performance for row update can be achieve with BEFORE UPDATE, but require to duplicate the logic.

It is not based on the already merged https://github.com/openmaptiles/openmaptiles/pull/896 because calling and update within a function for each updated row was not efficient for larger table (like housenumber).

It addresses #814.


* Remake update_peak_point use incremental update #814

* Make update_aerodrome_label_point use incremental update #814

* Make housenumber_centroid use incremental update #814

* Make update_continent_point use incremental update #814

* Make update_island_point use incremental update #814

* Make update_island_polygon use incremental update #814

* Remove dead code in update_state_point.sql

* Make update_state_point use incremental update #814

* Remove dead code in update_country_point.sql

* Make update_country_point use incremental update #814

* Make osm_poi_polygon use incremental update #814

Thanks @frodrigo

layers/place/update_continent_point.sql

@@ -1,22 +1,39 @@
 DROP TRIGGER IF EXISTS trigger_flag ON osm_continent_point;
+DROP TRIGGER IF EXISTS trigger_store ON osm_continent_point;
 DROP TRIGGER IF EXISTS trigger_refresh ON place_continent_point.updates;
 
+CREATE SCHEMA IF NOT EXISTS place_continent_point;
+
+CREATE TABLE IF NOT EXISTS place_continent_point.osm_ids
+(
+    osm_id bigint
+);
+
 -- etldoc:  osm_continent_point ->  osm_continent_point
-CREATE OR REPLACE FUNCTION update_osm_continent_point() RETURNS void AS
+CREATE OR REPLACE FUNCTION update_osm_continent_point(full_update boolean) RETURNS void AS
 $$
-BEGIN
     UPDATE osm_continent_point
     SET tags = update_tags(tags, geometry)
-    WHERE COALESCE(tags->'name:latin', tags->'name:nonlatin', tags->'name_int') IS NULL;
+    WHERE (full_update OR osm_id IN (SELECT osm_id FROM place_continent_point.osm_ids))
+      AND COALESCE(tags->'name:latin', tags->'name:nonlatin', tags->'name_int') IS NULL
+      AND tags != update_tags(tags, geometry);
+$$ LANGUAGE SQL;
 
-END;
-$$ LANGUAGE plpgsql;
-
-SELECT update_osm_continent_point();
+SELECT update_osm_continent_point(true);
 
 -- Handle updates
 
-CREATE SCHEMA IF NOT EXISTS place_continent_point;
+CREATE OR REPLACE FUNCTION place_continent_point.store() RETURNS trigger AS
+$$
+BEGIN
+    IF (tg_op = 'DELETE') THEN
+        INSERT INTO place_continent_point.osm_ids VALUES (OLD.osm_id);
+    ELSE
+        INSERT INTO place_continent_point.osm_ids VALUES (NEW.osm_id);
+    END IF;
+    RETURN NULL;
+END;
+$$ LANGUAGE plpgsql;
 
 CREATE TABLE IF NOT EXISTS place_continent_point.updates
 (
@@ -36,13 +53,21 @@ CREATE OR REPLACE FUNCTION place_continent_point.refresh() RETURNS trigger AS
 $$
 BEGIN
     RAISE LOG 'Refresh place_continent_point';
-    PERFORM update_osm_continent_point();
+    PERFORM update_osm_continent_point(false);
+    -- noinspection SqlWithoutWhere
+    DELETE FROM place_continent_point.osm_ids;
     -- noinspection SqlWithoutWhere
     DELETE FROM place_continent_point.updates;
     RETURN NULL;
 END;
 $$ LANGUAGE plpgsql;
 
+CREATE TRIGGER trigger_store
+    AFTER INSERT OR UPDATE OR DELETE
+    ON osm_continent_point
+    FOR EACH ROW
+EXECUTE PROCEDURE place_continent_point.store();
+
 CREATE TRIGGER trigger_flag
     AFTER INSERT OR UPDATE OR DELETE
     ON osm_continent_point