ace759590e
This PR allows queries to be parallelized on recent versions of Postgres. The `PARALLEL SAFE` modifier has been added to the layer functions and a PLPGSQL function to convert strings into number has been replaced. `PARALLEL SAFE` is a modifier for `CREATE FUNCTION` available since Postgres 9.6, so this change does not break current OpenMapTiles supported database version. More details about this topic [here](https://www.postgresql.org/docs/current/parallel-safety.html) and at the reference documentation for [`CREATE FUNCTION`](https://www.postgresql.org/docs/current/sql-createfunction.html). ### Testing procedure The procedure to test this was: * Imported `spain.pbf` in a clean environment * Dumped the OpenMapTiles database from the Postgres Docker image * Created a clean Postgres 12 database using the default Docker image * Installed `postgis` 3 from the default Debian package and `osml10n` 2.5.8 from the repository (`make`, etc.) * Restored the dump * Lowered the postgres planner parameters for triggering parallel plans: ```sql set parallel_setup_cost = 5; set parallel_tuple_cost = 0.005; ``` * Manually added the `PARALLEL SAFE` modifier to each function involved in layer queries (not on updates or inserting functions). * For each layer, run a testing query to confirm parallel workers were created, something like this: ```sql explain analyze select * from layer_aerodrome_label(tilebbox(8,128,95),10,null) union all select * from layer_aerodrome_label(tilebbox(8,128,97),10,null); ``` * After all the layers were processed and confirmed to start parallel executions, a more complete example was run. This example just retrieves the geometries for all the layers from the same tile but without using any MVT related function. <details><summary>Testing query</summary> ```sql -- Using the function layer_landuse explain analyze select geometry from layer_water(tilebbox(14,8020,6178),14) union all select geometry from layer_waterway(tilebbox(14,8020,6178),14) union all select geometry from layer_landcover(tilebbox(14,8020,6178),14) union all select geometry from layer_landuse(tilebbox(14,8020,6178),14) union all select geometry from layer_mountain_peak(tilebbox(14,8020,6178),14) union all select geometry from layer_park(tilebbox(14,8020,6178),14) union all select geometry from layer_boundary(tilebbox(14,8020,6178),14) union all select geometry from layer_aeroway(tilebbox(14,8020,6178),14) union all select geometry from layer_transportation(tilebbox(14,8020,6178),14) union all select geometry from layer_building(tilebbox(14,8020,6178),14) union all select geometry from layer_water_name(tilebbox(14,8020,6178),14) union all select geometry from layer_transportation_name(tilebbox(14,8020,6178),14) union all select geometry from layer_place(tilebbox(14,8020,6178),14) union all select geometry from layer_housenumber(tilebbox(14,8020,6178),14) union all select geometry from layer_poi(tilebbox(14,8020,6178),14) union all select geometry from layer_aerodrome_label(tilebbox(14,8020,6178),14); ``` </details> You can inspect the execution plan and results on [this page](https://explain.dalibo.com/plan/3z). Also [attaching](https://github.com/openmaptiles/openmaptiles/files/3951822/explain-tile-simple.tar.gz) the query and JSON output for future reference. The website gives a ton of details, but you may want to search for nodes mentioning `workers` or `parallel` like in this area referring to `osm_border` or `osm_aeroway_linestring` entities  ### Next steps Since the execution plan is not showing a parallel append at the top level, meaning it's not running each layer individually, I want to continue experimenting with parameters and queries to see if it's possible to even parallelize more the request. I will post my finding here, even no change in the code should happen. cc. @nyurik Co-authored-by: Yuri Astrakhan <yuriastrakhan@gmail.com>
58 lines
2.3 KiB
PL/PgSQL
58 lines
2.3 KiB
PL/PgSQL
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-- etldoc: layer_city[shape=record fillcolor=lightpink, style="rounded,filled",
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-- etldoc: label="layer_city | <z2_14> z2-z14+" ] ;
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-- etldoc: osm_city_point -> layer_city:z2_14
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CREATE OR REPLACE FUNCTION layer_city(bbox geometry, zoom_level int, pixel_width numeric)
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RETURNS TABLE(osm_id bigint, geometry geometry, name text, name_en text, name_de text, tags hstore, place city_place, "rank" int, capital int) AS $$
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SELECT * FROM (
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SELECT osm_id, geometry, name,
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COALESCE(NULLIF(name_en, ''), name) AS name_en,
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COALESCE(NULLIF(name_de, ''), name, name_en) AS name_de,
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tags,
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place, "rank", normalize_capital_level(capital) AS capital
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FROM osm_city_point
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WHERE geometry && bbox
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AND ((zoom_level = 2 AND "rank" = 1)
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OR (zoom_level BETWEEN 3 AND 7 AND "rank" <= zoom_level + 1)
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)
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UNION ALL
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SELECT osm_id, geometry, name,
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COALESCE(NULLIF(name_en, ''), name) AS name_en,
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COALESCE(NULLIF(name_de, ''), name, name_en) AS name_de,
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tags,
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place,
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COALESCE("rank", gridrank + 10),
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normalize_capital_level(capital) AS capital
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FROM (
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SELECT osm_id, geometry, name,
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COALESCE(NULLIF(name_en, ''), name) AS name_en,
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COALESCE(NULLIF(name_de, ''), name, name_en) AS name_de,
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tags,
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place, "rank", capital,
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row_number() OVER (
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PARTITION BY LabelGrid(geometry, 128 * pixel_width)
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ORDER BY "rank" ASC NULLS LAST,
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place ASC NULLS LAST,
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population DESC NULLS LAST,
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length(name) ASC
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)::int AS gridrank
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FROM osm_city_point
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WHERE geometry && bbox
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AND ((zoom_level = 7 AND place <= 'town'::city_place
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OR (zoom_level BETWEEN 8 AND 10 AND place <= 'village'::city_place)
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OR (zoom_level BETWEEN 11 AND 13 AND place <= 'suburb'::city_place)
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OR (zoom_level >= 14)
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))
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) AS ranked_places
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WHERE (zoom_level BETWEEN 7 AND 8 AND (gridrank <= 4 OR "rank" IS NOT NULL))
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OR (zoom_level = 9 AND (gridrank <= 8 OR "rank" IS NOT NULL))
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OR (zoom_level = 10 AND (gridrank <= 12 OR "rank" IS NOT NULL))
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OR (zoom_level BETWEEN 11 AND 12 AND (gridrank <= 14 OR "rank" IS NOT NULL))
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OR (zoom_level >= 13)
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) as city_all;
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$$
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LANGUAGE SQL
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IMMUTABLE PARALLEL SAFE;
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