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PostGIS expects a geometry type parameter when creating a Geometry column and permitted values include GEOMETRY, POINT, POLYGON, etc.

If I choose GEOMETRY then my Geometry column can store points, lines, polygons, etc, and if I choose POLYGON then the column can only store polygons. One obvious reason to use a specific geometry type such as POLYGON is to enforce a type constraint on insert / update.

Has anyone experienced performance gains from using a specific type over a generic type? For example, if I execute an ST_Intersects function against an equivalent number of GEOMETRY objects and POLYGON objects should I expect either operation to be faster?

To clarify - at this stage I'm only interested in PostGIS performance and I do not want to consider the cost of any additional complexity required in a database client that may need to handle each geometry type differently.

If I'm able to set aside some time I will attempt to test performance myself, but I would also like to hear anyone else's experience.

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    The C core types are encoded with the explicit geometry type, and most functions in PostGS do have to include a base check (against e.g. GEOS) to decide the most appropriate action for the compared geometry types. The index mechanics should not differ (much) between types themselves. I would expect most, if not all, available functions to perform equally on comparable data, no matter if the geometry typemod is specific or generic. – geozelot Jun 4 at 21:49
  • Accessing the data is also very important. For example, QGIS would scan every row of a geometry (generic) column when accessing it (adding the table, opening a project containing the said table, saving the project etc), while if the specific type+projection is set, the table is loaded directly. It can take several minutes to perform this validation... each time you touch the project/table – JGH Jun 6 at 12:01
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PostGIS indexes and functions are all coded to handle arbitrary geometry types. So there is no performance gain by using a more specific geometry typmod parameter.

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  • can you point to any documentation or direct experience to back this up? I don't doubt the accuracy of the statement, but decisions based on this could have cascading consequences so it would be good to have some additional confidence on the matter. – tomfumb Jun 7 at 16:07
  • This is base on my knowledge of the source code, and discussions with Paul Ramsey, the lead PostGIS developer and architect. So it's pretty solid. – dr_jts Jun 7 at 16:53

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