[PostGIS] #5899: pg_upgrade fails restore geography because spatial_ref_sys does not exist

[PostGIS]

#5899: pg_upgrade fails restore geography because spatial_ref_sys does not exist
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  Reporter:  robe     |      Owner:  pramsey
      Type:  defect   |     Status:  new
  Priority:  medium   |  Milestone:  PostGIS 3.7.0
 Component:  postgis  |    Version:  3.4.x
Resolution:           |   Keywords:
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Comment (by pramsey):

 I think I figured out a hack...

 In the code that looks up the SRID number and figures out how to represent
 it (as an "EPSG:XX" token, or a WKT string or a PROJ string) we first
 check for the existence of spatial_ref_sys, and then check for a non-zero
 size... if it cannot pass both these tests then we bypass it, and hand an
 "EPSG:XX" token directly into the proj lookup functions. This should, for
 cases where we have EPSG numbers that match, which is 99% of them, just
 Work. For people with custom codes, it will fail (still). For people with
 non-custom but non-epsg codes (French government?) it will fail (still).
 It does not FIX the problem, that requires pg_upgrade, but I think it
 dramatically lowers the affected footprint.
 Who is still screwed... people with custom srids or odd auth_name values
 who use an SRID in functions called in the schema or have non-4326
 geography srids in their schema.

 For anyone with a non-missing and non-zero-sized spatial_ref_sys table
 (mostly everyone) things should still work exactly the same.
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Ticket URL: <https://trac.osgeo.org/postgis/ticket/5899#comment:13>
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