Update PostGIS GEOS library on RDS

Question

I recently upgraded the PostGIS extension on my Postgres RDS instance. The upgrade went well, but the GEOS library is still on an old version. This means that some of the newer features are not available (e.g. ST_ReducePrecision).

Output of `SELECT postgis_full_version();`

```
POSTGIS="3.1.4 ded6c34" [EXTENSION] PGSQL="120" GEOS="3.8.2-CAPI-1.13.4" PROJ="6.2.1" GDAL="GDAL 2.3.1, released 2018/06/22" LIBXML="2.9.9" LIBJSON="0.12.99" LIBPROTOBUF="1.3.0" WAGYU="0.5.0 (Internal)" TOPOLOGY RASTER
```

Error message when using one of the newer features:
```
ERROR: Precision reduction requires GEOS-3.9 or higher
```

Is there a way to update the GEOS library?

Answer

Hi,

Are you sure you're running RDS Postgres and not Aurora Postgres? Based on the postgis_full_version I can't tell which engine or version you're using but RDS Postgres 13.5 has the following GEOS version available.

```
postgres=> select version(),postgis_full_version();
                                                 version                                                 |                                        postgis_full_version
---------------------------------------------------------------------------------------------------------+---------------------------------------------
 PostgreSQL 13.5 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-11), 64-bit | POSTGIS="3.1.4 ded6c34" [EXTENSION] PGSQL="130" GEOS="3.9.1-CAPI-1.14.2" PROJ="Rel. 5.2.0, September 15th, 2018" LIBXML="2.9.1" LIBJSON="0.13.1" LIBPROTOBUF="1.3.2" WAGYU="0.5.0 (Internal)"
(1 row)

```

Aurora Postgres 13.4 has the following GEOS version.

```
postgres=> select aurora_version(), version(), postgis_full_version();
 aurora_version |                                             version                                             |                                                                          p
ostgis_full_version
----------------+-------------------------------------------------------------------------------------------------+-----------------------------------
 13.4.0         | PostgreSQL 13.4 on x86_64-pc-linux-gnu, compiled by x86_64-pc-linux-gnu-gcc (GCC) 7.4.0, 64-bit | POSTGIS="3.1.4 ded6c34" [EXTENSION] PGSQL="130" GEOS="3.9.1dev-CAPI-1.14.1
" PROJ="6.2.1" LIBXML="2.9.9" LIBJSON="0.12.99" LIBPROTOBUF="1.3.0" WAGYU="0.5.0 (Internal)"
(1 row)

```

I'd recommend testing your postgis query on a test copy of one of these versions and if appropriate you could perform an engine version upgrade to pickup the required GEOS/postgis version.

Update PostGIS GEOS library on RDS

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