Make update_city_point use incremental update #814 (#951)

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) to 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.

It is a based on the already merged #944

It is a separated PR as less obvious than previous. It replaces the reset of the `rank` field to NULL by missing value resulting of `LEFT JOIN`. It avoid triggering a new update on the table by reset the value then re-seting it to initial or new value.

It addresses #814.

Thanks @frodrigo

Author: frodrigo

layers/place/update_city_point.sql

@@ -1,24 +1,27 @@
 DROP TRIGGER IF EXISTS trigger_flag ON osm_city_point;
+DROP TRIGGER IF EXISTS trigger_store ON osm_city_point;
 DROP TRIGGER IF EXISTS trigger_refresh ON place_city.updates;
 
 CREATE EXTENSION IF NOT EXISTS unaccent;
 
-CREATE OR REPLACE FUNCTION update_osm_city_point() RETURNS void AS
-$$
-BEGIN
+CREATE SCHEMA IF NOT EXISTS place_city;
 
-    -- Clear  OSM key:rank ( https://github.com/openmaptiles/openmaptiles/issues/108 )
-    -- etldoc: osm_city_point          -> osm_city_point
-    UPDATE osm_city_point AS osm SET "rank" = NULL WHERE "rank" IS NOT NULL;
+CREATE TABLE IF NOT EXISTS place_city.osm_ids
+(
+    osm_id bigint
+);
 
+CREATE OR REPLACE FUNCTION update_osm_city_point(full_update boolean) RETURNS void AS
+$$
     -- etldoc: ne_10m_populated_places -> osm_city_point
     -- etldoc: osm_city_point          -> osm_city_point
 
     WITH important_city_point AS (
-        SELECT osm.geometry, osm.osm_id, osm.name, osm.name_en, ne.scalerank, ne.labelrank
-        FROM ne_10m_populated_places AS ne,
-             osm_city_point AS osm
-        WHERE (
+        SELECT osm.osm_id, ne.scalerank
+        FROM osm_city_point AS osm
+             -- Clear OSM key:rank ( https://github.com/openmaptiles/openmaptiles/issues/108 )
+             LEFT JOIN ne_10m_populated_places AS ne ON
+            (
                 (osm.tags ? 'wikidata' AND osm.tags->'wikidata' = ne.wikidataid) OR
                 lower(osm.name) IN (lower(ne.name), lower(ne.namealt), lower(ne.meganame), lower(ne.gn_ascii), lower(ne.nameascii)) OR
                 lower(osm.name_en) IN (lower(ne.name), lower(ne.namealt), lower(ne.meganame), lower(ne.gn_ascii), lower(ne.nameascii)) OR
@@ -32,22 +35,35 @@ BEGIN
         -- are in the scalerank 5 bucket
     SET "rank" = CASE WHEN scalerank <= 5 THEN scalerank + 1 ELSE scalerank END
     FROM important_city_point AS ne
-    WHERE osm.osm_id = ne.osm_id;
+    WHERE (full_update OR osm.osm_id IN (SELECT osm_id FROM place_city.osm_ids))
+      AND rank IS DISTINCT FROM CASE WHEN scalerank <= 5 THEN scalerank + 1 ELSE scalerank END
+      AND osm.osm_id = ne.osm_id;
 
     UPDATE osm_city_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_city.osm_ids))
+      AND COALESCE(tags->'name:latin', tags->'name:nonlatin', tags->'name_int') IS NULL
+      AND tags != update_tags(tags, geometry);
 
-END;
-$$ LANGUAGE plpgsql;
+$$ LANGUAGE SQL;
 
-SELECT update_osm_city_point();
+SELECT update_osm_city_point(true);
 
 CREATE INDEX IF NOT EXISTS osm_city_point_rank_idx ON osm_city_point ("rank");
 
 -- Handle updates
 
-CREATE SCHEMA IF NOT EXISTS place_city;
+CREATE OR REPLACE FUNCTION place_city.store() RETURNS trigger AS
+$$
+BEGIN
+    IF (tg_op = 'DELETE') THEN
+        INSERT INTO place_city.osm_ids VALUES (OLD.osm_id);
+    ELSE
+        INSERT INTO place_city.osm_ids VALUES (NEW.osm_id);
+    END IF;
+    RETURN NULL;
+END;
+$$ LANGUAGE plpgsql;
 
 CREATE TABLE IF NOT EXISTS place_city.updates
 (
@@ -67,13 +83,21 @@ CREATE OR REPLACE FUNCTION place_city.refresh() RETURNS trigger AS
 $$
 BEGIN
     RAISE LOG 'Refresh place_city rank';
-    PERFORM update_osm_city_point();
+    PERFORM update_osm_city_point(false);
+    -- noinspection SqlWithoutWhere
+    DELETE FROM place_city.osm_ids;
     -- noinspection SqlWithoutWhere
     DELETE FROM place_city.updates;
     RETURN NULL;
 END;
 $$ LANGUAGE plpgsql;
 
+CREATE TRIGGER trigger_store
+    AFTER INSERT OR UPDATE OR DELETE
+    ON osm_city_point
+    FOR EACH ROW
+EXECUTE PROCEDURE place_city.store();
+
 CREATE TRIGGER trigger_flag
     AFTER INSERT OR UPDATE OR DELETE
     ON osm_city_point