> The flat node store stores the raw coordinates as they come from OSM before
> any kind of projection.
This is what I suspected, but makes this difference in performance a bit
puzzling. When running these tests, I always fully reboot my host machine, and
restart my shut-down virtual machine to ensure the conditions are as similar as
possible.
Results of bench-marking Facebook Daylight over the last year using this method
have proven really consistent. With my own custom style, I have also seen
nearly 7000k/s node loading speed for osm2pgsql v1.10 and v1.11. Switching to
v2.0.0 and now v2.0.1, I saw a very minor drop in speed to the listed
+/-5800k/s, maybe due to some changes in the latest release, that was
consistent for all v2.0.x releases.
One interesting thing I now noticed though in pgAdmin, is that during the node
loading stage, that pgAdmin besides the active COPY session of osm2pgsql, shows
a secondary "idle" session with wait event "Client:ClientRead". However,
puzzling enough, the actual SQL differs between my custom flex style (based on
an adaptation by Paul Norman's variant of an openstreetmap-carto flex style),
and the now official 'openstreetmap-carto-flex' LUA style you developed.
For my style, the waiting session shows a:
`CREATE UNLOGGED TABLE <TABLE_NAME>...`
type statement, while for your style it consistently shows:
`CREATE TRIGGER "planet_osm_line_osm2pgsql_valid" BEFORE INSERT OR UPDATE ON
"osm"."planet_osm_line" FOR EACH ROW EXECUTE PROCEDURE
"osm"."planet_osm_line_osm2pgsql_valid"()`
as the idle session SQL.
I wonder if this idle thread, and the difference in SQL, is somehow responsible
for the difference in loading speed by holding onto some resources.
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