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Implement non-blocking refresh (#1308)

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This PR implements non-blocking updates in the park layer.

The approach was to use the `REFRESH MATERIALIZED VIEW CONCURRENTLY` feature in postgres.  In order to achieve this, a unique index was added on the z4 dissolved park area table.  The `ST_Union` / `ST_Dump` sequence was changed to an explicit cluster DB scan (an equivalent operation) so that a unique osm ID could be generated from each dissolved polygon.

Below is a screen shot from Idaho, USA showing that the dissolved z4 still works as expected.

![image](https://user-images.githubusercontent.com/3254090/142341513-588045f0-7757-4acd-99e5-a50bbe6b0682.png)
This commit is contained in:
Brian Sperlongano 2021-11-24 05:17:29 -05:00 committed by GitHub
parent cdff735be1
commit 0cff3449b5
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1 changed files with 11 additions and 5 deletions
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16
layers/park/update_park_polygon.sql
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@ -23,11 +23,17 @@ ALTER TABLE osm_park_polygon_gen_z5
DROP MATERIALIZED VIEW IF EXISTS osm_park_polygon_dissolve_z4 CASCADE; DROP MATERIALIZED VIEW IF EXISTS osm_park_polygon_dissolve_z4 CASCADE;
CREATE MATERIALIZED VIEW osm_park_polygon_dissolve_z4 AS CREATE MATERIALIZED VIEW osm_park_polygon_dissolve_z4 AS
( (
SELECT SELECT min(osm_id) AS osm_id,
(ST_Dump( ST_Union(geometry) AS geometry
ST_Union(geometry))).geom AS geometry FROM (
FROM osm_park_polygon_gen_z4 SELECT ST_ClusterDBSCAN(geometry, 0, 1) OVER() AS cluster,
osm_id,
geometry
FROM osm_park_polygon_gen_z4
) park_cluster
GROUP BY cluster
); );
CREATE UNIQUE INDEX IF NOT EXISTS osm_park_polygon_dissolve_idx ON osm_park_polygon_dissolve_z4 (osm_id);
DROP TRIGGER IF EXISTS update_row ON osm_park_polygon; DROP TRIGGER IF EXISTS update_row ON osm_park_polygon;
DROP TRIGGER IF EXISTS update_row ON osm_park_polygon_gen_z13; DROP TRIGGER IF EXISTS update_row ON osm_park_polygon_gen_z13;
@ -95,7 +101,7 @@ BEGIN
SET tags = update_tags(tags, geometry), SET tags = update_tags(tags, geometry),
geometry_point = st_centroid(geometry); geometry_point = st_centroid(geometry);
REFRESH MATERIALIZED VIEW osm_park_polygon_dissolve_z4; REFRESH MATERIALIZED VIEW CONCURRENTLY osm_park_polygon_dissolve_z4;
END; END;
$$ LANGUAGE plpgsql; $$ LANGUAGE plpgsql;