Parallel capability to layer functions (#728)

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

![image](https://user-images.githubusercontent.com/188264/70647153-9cac9300-1c48-11ea-96ea-ac7a1e2f4a79.png)

### 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>

layers/aerodrome_label/layer.sql

@@ -36,5 +36,6 @@ $$
     round(substring(ele from E'^(-?\\d+)(\\D|$)')::int*3.2808399)::int AS ele_ft
   FROM osm_aerodrome_label_point
   WHERE geometry && bbox AND zoom_level >= 10;
-
-$$ LANGUAGE SQL IMMUTABLE;
+$$
+LANGUAGE SQL
+IMMUTABLE PARALLEL SAFE;

layers/aeroway/layer.sql

@@ -40,4 +40,6 @@ RETURNS TABLE(geometry geometry, class text, ref text) AS $$
         FROM osm_aeroway_polygon WHERE zoom_level >= 14
     ) AS zoom_levels
     WHERE geometry && bbox;
-$$ LANGUAGE SQL IMMUTABLE;
+$$
+LANGUAGE SQL IMMUTABLE
+PARALLEL SAFE;

layers/boundary/boundary.sql

@@ -470,4 +470,6 @@ RETURNS TABLE(geometry geometry, admin_level int, disputed int, disputed_name te
         -- etldoc: boundary_z13 -> layer_boundary:z13
         SELECT * FROM boundary_z13 WHERE geometry && bbox AND zoom_level >= 13
     ) AS zoom_levels;
-$$ LANGUAGE SQL IMMUTABLE;
+$$
+LANGUAGE SQL IMMUTABLE
+PARALLEL SAFE;

layers/building/building.sql

@@ -142,6 +142,8 @@ RETURNS TABLE(geometry geometry, osm_id bigint, render_height int, render_min_he
             zoom_level >= 14 AND geometry && bbox
     ) AS zoom_levels
     ORDER BY render_height ASC, ST_YMin(geometry) DESC;
-$$ LANGUAGE SQL IMMUTABLE;
+$$
+LANGUAGE SQL IMMUTABLE
+PARALLEL SAFE;
 
 -- not handled: where a building outline covers building parts

layers/housenumber/layer.sql

@@ -7,4 +7,6 @@ RETURNS TABLE(osm_id bigint, geometry geometry, housenumber text) AS $$
    -- etldoc: osm_housenumber_point -> layer_housenumber:z14_
     SELECT osm_id, geometry, housenumber FROM osm_housenumber_point
     WHERE zoom_level >= 14 AND geometry && bbox;
-$$ LANGUAGE SQL IMMUTABLE;
+$$
+LANGUAGE SQL
+IMMUTABLE PARALLEL SAFE;

layers/landcover/landcover.sql

@@ -13,7 +13,9 @@ CREATE OR REPLACE FUNCTION landcover_class(subclass VARCHAR) RETURNS TEXT AS $$
     SELECT CASE
         %%FIELD_MAPPING: class %%
     END;
-$$ LANGUAGE SQL IMMUTABLE;
+$$
+LANGUAGE SQL
+IMMUTABLE PARALLEL SAFE;
 
 -- etldoc: ne_110m_glaciated_areas ->  landcover_z0
 CREATE OR REPLACE VIEW landcover_z0 AS (
@@ -128,4 +130,6 @@ RETURNS TABLE(osm_id bigint, geometry geometry, class text, subclass text) AS $$
         SELECT *
         FROM landcover_z14 WHERE zoom_level >= 14 AND geometry && bbox
     ) AS zoom_levels;
-$$ LANGUAGE SQL IMMUTABLE;
+$$
+LANGUAGE SQL
+IMMUTABLE PARALLEL SAFE;

layers/landuse/landuse.sql

@@ -108,4 +108,6 @@ RETURNS TABLE(osm_id bigint, geometry geometry, class text) AS $$
         SELECT * FROM landuse_z14 WHERE zoom_level >= 14
     ) AS zoom_levels
     WHERE geometry && bbox;
-$$ LANGUAGE SQL IMMUTABLE;
+$$
+LANGUAGE SQL
+IMMUTABLE PARALLEL SAFE;

layers/mountain_peak/layer.sql

@@ -52,4 +52,6 @@ $$
   WHERE zoom_level >= 7 AND (rank <= 5 OR zoom_level >= 14)
   ORDER BY "rank" ASC;
 
-$$ LANGUAGE SQL IMMUTABLE;
+$$
+LANGUAGE SQL
+IMMUTABLE PARALLEL SAFE;

layers/park/layer.sql

@@ -122,4 +122,6 @@ RETURNS TABLE(osm_id bigint, geometry geometry, class text, name text, name_en t
         WHERE zoom_level >= 14 AND geometry_point && bbox
     ) AS park_point
     ) AS park_all;
-$$ LANGUAGE SQL IMMUTABLE;
+$$
+LANGUAGE SQL
+IMMUTABLE PARALLEL SAFE;

layers/place/capital.sql

@@ -4,4 +4,6 @@ RETURNS INT AS $$
         WHEN capital IN ('yes', '2') THEN 2
         WHEN capital = '4' THEN 4
     END;
-$$ LANGUAGE SQL IMMUTABLE STRICT;
+$$
+LANGUAGE SQL
+IMMUTABLE STRICT PARALLEL SAFE;

layers/place/city.sql

@@ -52,4 +52,6 @@ RETURNS TABLE(osm_id bigint, geometry geometry, name text, name_en text, name_de
        OR (zoom_level BETWEEN 11 AND 12 AND (gridrank <= 14 OR "rank" IS NOT NULL))
        OR (zoom_level >= 13)
   ) as city_all;
-$$ LANGUAGE SQL IMMUTABLE;
+$$
+LANGUAGE SQL
+IMMUTABLE PARALLEL SAFE;

layers/place/island_rank.sql

@@ -6,4 +6,6 @@ CREATE OR REPLACE FUNCTION island_rank(area REAL) RETURNS INT AS $$
         WHEN area > 40000000 THEN 3
         ELSE 7
     END;
-$$ LANGUAGE SQL IMMUTABLE STRICT;
+$$
+LANGUAGE SQL
+IMMUTABLE STRICT PARALLEL SAFE;

layers/place/layer.sql

@@ -96,4 +96,6 @@ RETURNS TABLE(osm_id bigint, geometry geometry, name text, name_en text,
     FROM layer_city(bbox, zoom_level, pixel_width)
     ORDER BY "rank" ASC
     ) AS place_all
-$$ LANGUAGE SQL IMMUTABLE;
+$$
+LANGUAGE SQL
+IMMUTABLE PARALLEL SAFE;

layers/poi/class.sql

@@ -25,7 +25,9 @@ RETURNS INT AS $$
         WHEN 'bar' THEN 800
         ELSE 1000
     END;
-$$ LANGUAGE SQL IMMUTABLE;
+$$
+LANGUAGE SQL
+IMMUTABLE PARALLEL SAFE;
 
 CREATE OR REPLACE FUNCTION poi_class(subclass TEXT, mapping_key TEXT)
 RETURNS TEXT AS $$
@@ -33,4 +35,6 @@ RETURNS TEXT AS $$
         %%FIELD_MAPPING: class %%
         ELSE subclass
     END;
-$$ LANGUAGE SQL IMMUTABLE;
+$$
+LANGUAGE SQL
+IMMUTABLE PARALLEL SAFE;

layers/poi/layer.sql

@@ -70,4 +70,6 @@ RETURNS TABLE(osm_id bigint, geometry geometry, name text, name_en text, name_de
         ) as poi_union
     ORDER BY "rank"
     ;
-$$ LANGUAGE SQL IMMUTABLE;
+$$
+LANGUAGE SQL
+IMMUTABLE PARALLEL SAFE;

layers/transportation/class.sql

@@ -4,7 +4,9 @@ CREATE OR REPLACE FUNCTION brunnel(is_bridge BOOL, is_tunnel BOOL, is_ford BOOL)
         WHEN is_tunnel THEN 'tunnel'
         WHEN is_ford THEN 'ford'
     END;
-$$ LANGUAGE SQL IMMUTABLE STRICT;
+$$
+LANGUAGE SQL
+IMMUTABLE STRICT PARALLEL SAFE;
 
 -- The classes for highways are derived from the classes used in ClearTables
 -- https://github.com/ClearTables/ClearTables/blob/master/transportation.lua
@@ -12,7 +14,9 @@ CREATE OR REPLACE FUNCTION highway_class(highway TEXT, public_transport TEXT, co
     SELECT CASE
         %%FIELD_MAPPING: class %%
     END;
-$$ LANGUAGE SQL IMMUTABLE;
+$$
+LANGUAGE SQL
+IMMUTABLE PARALLEL SAFE;
 
 -- The classes for railways are derived from the classes used in ClearTables
 -- https://github.com/ClearTables/ClearTables/blob/master/transportation.lua
@@ -21,7 +25,9 @@ CREATE OR REPLACE FUNCTION railway_class(railway TEXT) RETURNS TEXT AS $$
         WHEN railway IN ('rail', 'narrow_gauge', 'preserved', 'funicular') THEN 'rail'
         WHEN railway IN ('subway', 'light_rail', 'monorail', 'tram') THEN 'transit'
     END;
-$$ LANGUAGE SQL IMMUTABLE STRICT;
+$$
+LANGUAGE SQL
+IMMUTABLE STRICT PARALLEL SAFE;
 
 -- Limit service to only the most important values to ensure
 -- we always know the values of service
@@ -29,7 +35,9 @@ CREATE OR REPLACE FUNCTION service_value(service TEXT) RETURNS TEXT AS $$
     SELECT CASE
         WHEN service IN ('spur', 'yard', 'siding', 'crossover', 'driveway', 'alley', 'parking_aisle') THEN service
     END;
-$$ LANGUAGE SQL IMMUTABLE STRICT;
+$$
+LANGUAGE SQL
+IMMUTABLE STRICT PARALLEL SAFE;
 
 -- Limit surface to only the most important values to ensure
 -- we always know the values of surface
@@ -38,4 +46,6 @@ CREATE OR REPLACE FUNCTION surface_value(surface TEXT) RETURNS TEXT AS $$
         WHEN surface IN ('paved', 'asphalt', 'cobblestone', 'concrete', 'concrete:lanes', 'concrete:plates', 'metal', 'paving_stones', 'sett', 'unhewn_cobblestone', 'wood') THEN 'paved'
         WHEN surface IN ('unpaved', 'compacted', 'dirt', 'earth', 'fine_gravel', 'grass', 'grass_paver', 'gravel', 'gravel_turf', 'ground', 'ice', 'mud', 'pebblestone', 'salt', 'sand', 'snow', 'woodchips') THEN 'unpaved'
     END;
-$$ LANGUAGE SQL IMMUTABLE STRICT;
+$$
+LANGUAGE SQL
+IMMUTABLE STRICT PARALLEL SAFE;

layers/transportation/layer.sql

@@ -1,6 +1,8 @@
 CREATE OR REPLACE FUNCTION highway_is_link(highway TEXT) RETURNS BOOLEAN AS $$
     SELECT highway LIKE '%_link';
-$$ LANGUAGE SQL IMMUTABLE STRICT;
+$$
+LANGUAGE SQL
+IMMUTABLE STRICT PARALLEL SAFE;
 
 
 -- etldoc: layer_transportation[shape=record fillcolor=lightpink, style="rounded,filled",
@@ -366,4 +368,6 @@ indoor INT, bicycle TEXT, foot TEXT, horse TEXT, mtb_scale TEXT, surface TEXT) A
     ) AS zoom_levels
     WHERE geometry && bbox
     ORDER BY z_order ASC;
-$$ LANGUAGE SQL IMMUTABLE;
+$$
+LANGUAGE SQL
+IMMUTABLE PARALLEL SAFE;

layers/transportation_name/layer.sql

@@ -126,4 +126,6 @@ RETURNS TABLE(osm_id bigint, geometry geometry, name text, name_en text,
     ) AS zoom_levels
     WHERE geometry && bbox
     ORDER BY z_order ASC;
-$$ LANGUAGE SQL IMMUTABLE;
+$$
+LANGUAGE SQL
+IMMUTABLE PARALLEL SAFE;

layers/water/water.sql

@@ -48,7 +48,9 @@ CREATE OR REPLACE FUNCTION water_class(waterway TEXT) RETURNS TEXT AS $$
            %%FIELD_MAPPING: class %%
            ELSE 'river'
    END;
-$$ LANGUAGE SQL IMMUTABLE;
+$$
+LANGUAGE SQL
+IMMUTABLE PARALLEL SAFE;
 
 
 CREATE OR REPLACE FUNCTION waterway_brunnel(is_bridge BOOL, is_tunnel BOOL) RETURNS TEXT AS $$
@@ -56,7 +58,9 @@ CREATE OR REPLACE FUNCTION waterway_brunnel(is_bridge BOOL, is_tunnel BOOL) RETU
         WHEN is_bridge THEN 'bridge'
         WHEN is_tunnel THEN 'tunnel'
     END;
-$$ LANGUAGE SQL IMMUTABLE STRICT;
+$$
+LANGUAGE SQL
+IMMUTABLE STRICT PARALLEL SAFE;
 
 
 
@@ -375,4 +379,6 @@ RETURNS TABLE(geometry geometry, class text, brunnel text, intermittent int) AS
         SELECT * FROM water_z14 WHERE zoom_level >= 14
     ) AS zoom_levels
     WHERE geometry && bbox;
-$$ LANGUAGE SQL IMMUTABLE;
+$$
+LANGUAGE SQL
+IMMUTABLE PARALLEL SAFE;

layers/water_name/layer.sql

@@ -54,4 +54,6 @@ RETURNS TABLE(osm_id bigint, geometry geometry, name text, name_en text, name_de
         OR (zoom_level >= "rank" AND "rank" IS NOT NULL)
         OR (zoom_level >= 8)
     );
-$$ LANGUAGE SQL IMMUTABLE;
+$$
+LANGUAGE SQL
+IMMUTABLE PARALLEL SAFE;

layers/waterway/waterway.sql

@@ -3,7 +3,9 @@ CREATE OR REPLACE FUNCTION waterway_brunnel(is_bridge BOOL, is_tunnel BOOL) RETU
         WHEN is_bridge THEN 'bridge'
         WHEN is_tunnel THEN 'tunnel'
     END;
-$$ LANGUAGE SQL IMMUTABLE STRICT;
+$$
+LANGUAGE SQL
+IMMUTABLE STRICT PARALLEL SAFE;
 
 -- etldoc: ne_110m_rivers_lake_centerlines ->  waterway_z3
 CREATE OR REPLACE VIEW waterway_z3 AS (
@@ -105,4 +107,6 @@ RETURNS TABLE(geometry geometry, class text, name text, name_en text, name_de te
         SELECT * FROM waterway_z14 WHERE zoom_level >= 14
     ) AS zoom_levels
     WHERE geometry && bbox;
-$$ LANGUAGE SQL IMMUTABLE;
+$$
+LANGUAGE SQL
+IMMUTABLE PARALLEL SAFE;