Jorge Sanz ace759590e
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>
2020-01-31 19:36:02 -05:00

113 lines
5.1 KiB
PL/PgSQL

CREATE OR REPLACE FUNCTION waterway_brunnel(is_bridge BOOL, is_tunnel BOOL) RETURNS TEXT AS $$
SELECT CASE
WHEN is_bridge THEN 'bridge'
WHEN is_tunnel THEN 'tunnel'
END;
$$
LANGUAGE SQL
IMMUTABLE STRICT PARALLEL SAFE;
-- etldoc: ne_110m_rivers_lake_centerlines -> waterway_z3
CREATE OR REPLACE VIEW waterway_z3 AS (
SELECT geometry, 'river'::text AS class, NULL::text AS name, NULL::text AS name_en, NULL::text AS name_de, NULL::hstore AS tags, NULL::boolean AS is_bridge, NULL::boolean AS is_tunnel, NULL::boolean AS is_intermittent
FROM ne_110m_rivers_lake_centerlines
WHERE featurecla = 'River'
);
-- etldoc: ne_50m_rivers_lake_centerlines -> waterway_z4
CREATE OR REPLACE VIEW waterway_z4 AS (
SELECT geometry, 'river'::text AS class, NULL::text AS name, NULL::text AS name_en, NULL::text AS name_de, NULL::hstore AS tags, NULL::boolean AS is_bridge, NULL::boolean AS is_tunnel, NULL::boolean AS is_intermittent
FROM ne_50m_rivers_lake_centerlines
WHERE featurecla = 'River'
);
-- etldoc: ne_10m_rivers_lake_centerlines -> waterway_z6
CREATE OR REPLACE VIEW waterway_z6 AS (
SELECT geometry, 'river'::text AS class, NULL::text AS name, NULL::text AS name_en, NULL::text AS name_de, NULL::hstore AS tags, NULL::boolean AS is_bridge, NULL::boolean AS is_tunnel, NULL::boolean AS is_intermittent
FROM ne_10m_rivers_lake_centerlines
WHERE featurecla = 'River'
);
-- etldoc: osm_important_waterway_linestring_gen3 -> waterway_z9
CREATE OR REPLACE VIEW waterway_z9 AS (
SELECT geometry, 'river'::text AS class, name, name_en, name_de, tags, NULL::boolean AS is_bridge, NULL::boolean AS is_tunnel, NULL::boolean AS is_intermittent
FROM osm_important_waterway_linestring_gen3
);
-- etldoc: osm_important_waterway_linestring_gen2 -> waterway_z10
CREATE OR REPLACE VIEW waterway_z10 AS (
SELECT geometry, 'river'::text AS class, name, name_en, name_de, tags, NULL::boolean AS is_bridge, NULL::boolean AS is_tunnel, NULL::boolean AS is_intermittent
FROM osm_important_waterway_linestring_gen2
);
-- etldoc:osm_important_waterway_linestring_gen1 -> waterway_z11
CREATE OR REPLACE VIEW waterway_z11 AS (
SELECT geometry, 'river'::text AS class, name, name_en, name_de, tags, NULL::boolean AS is_bridge, NULL::boolean AS is_tunnel, NULL::boolean AS is_intermittent
FROM osm_important_waterway_linestring_gen1
);
-- etldoc: osm_waterway_linestring -> waterway_z12
CREATE OR REPLACE VIEW waterway_z12 AS (
SELECT geometry, waterway::text AS class, name, name_en, name_de, tags, is_bridge, is_tunnel, is_intermittent
FROM osm_waterway_linestring
WHERE waterway IN ('river', 'canal')
);
-- etldoc: osm_waterway_linestring -> waterway_z13
CREATE OR REPLACE VIEW waterway_z13 AS (
SELECT geometry, waterway::text AS class, name, name_en, name_de, tags, is_bridge, is_tunnel, is_intermittent
FROM osm_waterway_linestring
WHERE waterway IN ('river', 'canal', 'stream', 'drain', 'ditch')
);
-- etldoc: osm_waterway_linestring -> waterway_z14
CREATE OR REPLACE VIEW waterway_z14 AS (
SELECT geometry, waterway::text AS class, name, name_en, name_de, tags, is_bridge, is_tunnel, is_intermittent
FROM osm_waterway_linestring
);
-- etldoc: layer_waterway[shape=record fillcolor=lightpink, style="rounded,filled",
-- etldoc: label="layer_waterway | <z3> z3 |<z4_5> z4-z5 |<z6_8> z6-8 | <z9> z9 |<z10> z10 |<z11> z11 |<z12> z12|<z13> z13|<z14> z14+" ];
CREATE OR REPLACE FUNCTION layer_waterway(bbox geometry, zoom_level int)
RETURNS TABLE(geometry geometry, class text, name text, name_en text, name_de text, brunnel text, intermittent int, tags hstore) AS $$
SELECT geometry, class,
NULLIF(name, '') AS name,
COALESCE(NULLIF(name_en, ''), name) AS name_en,
COALESCE(NULLIF(name_de, ''), name, name_en) AS name_de,
waterway_brunnel(is_bridge, is_tunnel) AS brunnel,
is_intermittent::int AS intermittent,
tags
FROM (
-- etldoc: waterway_z3 -> layer_waterway:z3
SELECT * FROM waterway_z3 WHERE zoom_level = 3
UNION ALL
-- etldoc: waterway_z4 -> layer_waterway:z4_5
SELECT * FROM waterway_z4 WHERE zoom_level BETWEEN 4 AND 5
UNION ALL
-- etldoc: waterway_z6 -> layer_waterway:z6_8
SELECT * FROM waterway_z6 WHERE zoom_level BETWEEN 6 AND 8
UNION ALL
-- etldoc: waterway_z9 -> layer_waterway:z9
SELECT * FROM waterway_z9 WHERE zoom_level = 9
UNION ALL
-- etldoc: waterway_z10 -> layer_waterway:z10
SELECT * FROM waterway_z10 WHERE zoom_level = 10
UNION ALL
-- etldoc: waterway_z11 -> layer_waterway:z11
SELECT * FROM waterway_z11 WHERE zoom_level = 11
UNION ALL
-- etldoc: waterway_z12 -> layer_waterway:z12
SELECT * FROM waterway_z12 WHERE zoom_level = 12
UNION ALL
-- etldoc: waterway_z13 -> layer_waterway:z13
SELECT * FROM waterway_z13 WHERE zoom_level = 13
UNION ALL
-- etldoc: waterway_z14 -> layer_waterway:z14
SELECT * FROM waterway_z14 WHERE zoom_level >= 14
) AS zoom_levels
WHERE geometry && bbox;
$$
LANGUAGE SQL
IMMUTABLE PARALLEL SAFE;