[postgis-tickets] [PostGIS] #4372: PROJ 6: 4x slowdown over points

[PostGIS]

#4372: PROJ 6: 4x slowdown over points
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  Reporter:  Algunenano  |      Owner:  Algunenano
      Type:  defect      |     Status:  assigned
  Priority:  high        |  Milestone:  PostGIS 3.0.0
 Component:  postgis     |    Version:  trunk
Resolution:              |   Keywords:
-------------------------+---------------------------

Comment (by Algunenano):

 I've replaced the PR with https://github.com/postgis/postgis/pull/423

 What this does:
 - Cleans up configure.ac when running under PROJ6 (avoids error message
 that its ignored).

 - PROJ 6+ (and only 6+):
   - Caches source_swapped / target_swapped for all PJs. This brings
 ST_Transform to, more or less, almost the same performance as 5.1 (except
 the first row, which creates the PJ).
   - Caches source_is_latlong / source_semi_major_metre /
 source_semi_minor_metre when required (source srid == target srid). This
 brings a bunch of functions (ST_AsTWKB, geography functions) to, more or
 less, the same performance as before (except the first row, which creates
 the PJ).
   - Uses `proj_trans` instead of `proj_trans_generic` for single points
 (faster and makes it on par of 5.2 performance for that case).

 - PROJ (all releases):
   - Allocate auxiliar memory (LWPROJ / PJ) in the parent memory context
 instead of manually using malloc/free.
   - Avoid double lookup (one to check if the item is in the cache, one for
 retrieval).
   - Increases PROJ_CACHE_ITEMS from **16** to **128**.
 PROJ_BACKEND_HASH_SIZE goes from **32** to **256**. This is to minimize
 the huge impact of creating projections between 5.2 and 6.1, specially for
 ST_Buffer(geography) which autogenerates srids based on
 `SRID_RESERVE_OFFSET`. There are over 120+ used SRIDs in that range, so
 deleting and recreating PJs is a huge performance loss (it isn't as bad
 for 5.1 since PJ creation is much faster).
   - Removes the call to `proj_context_set_search_paths`. AFAIK, we don't
 distribute proj files anymore so this is legacy. It's also preventing the
 default proj installation of finding proj.db and using the fallback method
 (faster but more imprecise). If it breaks something, I'll consider reading
 it just for Windows (as it's mentioned in the comments of the function).

 Any comments are welcome. I'll try to break this down into several commits
 for clarity.

-- 
Ticket URL: <https://trac.osgeo.org/postgis/ticket/4372#comment:11>
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