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

132 lines
4.4 KiB
PL/PgSQL

-- etldoc: layer_transportation_name[shape=record fillcolor=lightpink, style="rounded,filled",
-- etldoc: label="layer_transportation_name | <z6> z6 | <z7> z7 | <z8> z8 |<z9> z9 |<z10> z10 |<z11> z11 |<z12> z12|<z13> z13|<z14_> z14+" ] ;
CREATE OR REPLACE FUNCTION layer_transportation_name(bbox geometry, zoom_level integer)
RETURNS TABLE(osm_id bigint, geometry geometry, name text, name_en text,
name_de text, tags hstore, ref text, ref_length int, network text, class
text, subclass text, layer INT, level INT, indoor INT) AS $$
SELECT osm_id, geometry,
NULLIF(name, '') AS name,
COALESCE(NULLIF(name_en, ''), name) AS name_en,
COALESCE(NULLIF(name_de, ''), name, name_en) AS name_de,
tags,
NULLIF(ref, ''), NULLIF(LENGTH(ref), 0) AS ref_length,
--TODO: The road network of the road is not yet implemented
case
when network is not null
then network::text
when length(coalesce(ref, ''))>0
then 'road'
end as network,
highway_class(highway, '', construction) AS class,
CASE
WHEN highway IS NOT NULL AND highway_class(highway, '', construction) = 'path'
THEN highway
END AS subclass,
NULLIF(layer, 0) AS layer,
"level",
CASE WHEN indoor=TRUE THEN 1 END as indoor
FROM (
-- etldoc: osm_transportation_name_linestring_gen4 -> layer_transportation_name:z6
SELECT *,
NULL::int AS layer, NULL::int AS level, NULL::boolean AS indoor
FROM osm_transportation_name_linestring_gen4
WHERE zoom_level = 6
UNION ALL
-- etldoc: osm_transportation_name_linestring_gen3 -> layer_transportation_name:z7
SELECT *,
NULL::int AS layer, NULL::int AS level, NULL::boolean AS indoor
FROM osm_transportation_name_linestring_gen3
WHERE zoom_level = 7
UNION ALL
-- etldoc: osm_transportation_name_linestring_gen2 -> layer_transportation_name:z8
SELECT *,
NULL::int AS layer, NULL::int AS level, NULL::boolean AS indoor
FROM osm_transportation_name_linestring_gen2
WHERE zoom_level = 8
UNION ALL
-- etldoc: osm_transportation_name_linestring_gen1 -> layer_transportation_name:z9
-- etldoc: osm_transportation_name_linestring_gen1 -> layer_transportation_name:z10
-- etldoc: osm_transportation_name_linestring_gen1 -> layer_transportation_name:z11
SELECT *,
NULL::int AS layer, NULL::int AS level, NULL::boolean AS indoor
FROM osm_transportation_name_linestring_gen1
WHERE zoom_level BETWEEN 9 AND 11
UNION ALL
-- etldoc: osm_transportation_name_linestring -> layer_transportation_name:z12
SELECT
geometry,
osm_id,
name,
name_en,
name_de,
"tags",
ref,
highway,
construction,
network,
z_order,
layer,
"level",
indoor
FROM osm_transportation_name_linestring
WHERE zoom_level = 12
AND LineLabel(zoom_level, COALESCE(NULLIF(name, ''), ref), geometry)
AND highway_class(highway, '', construction) NOT IN ('minor', 'track', 'path')
AND NOT highway_is_link(highway)
UNION ALL
-- etldoc: osm_transportation_name_linestring -> layer_transportation_name:z13
SELECT
geometry,
osm_id,
name,
name_en,
name_de,
"tags",
ref,
highway,
construction,
network,
z_order,
layer,
"level",
indoor
FROM osm_transportation_name_linestring
WHERE zoom_level = 13
AND LineLabel(zoom_level, COALESCE(NULLIF(name, ''), ref), geometry)
AND highway_class(highway, '', construction) NOT IN ('track', 'path')
UNION ALL
-- etldoc: osm_transportation_name_linestring -> layer_transportation_name:z14_
SELECT
geometry,
osm_id,
name,
name_en,
name_de,
"tags",
ref,
highway,
construction,
network,
z_order,
layer,
"level",
indoor
FROM osm_transportation_name_linestring
WHERE zoom_level >= 14
) AS zoom_levels
WHERE geometry && bbox
ORDER BY z_order ASC;
$$
LANGUAGE SQL
IMMUTABLE PARALLEL SAFE;