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- Log -----------------------------------------------------------------
commit 77cae92a57d2de888eca1993d2c4842258f8d93d
Author: Regina Obe <lr at pcorp.us>
Date:   Thu Aug 25 17:56:55 2022 -0400

    Tip about how to upgrade postgis-sfcgal from < PostGIS 3.1

diff --git a/content/post/2017/06-05_postgis-backend-is-already-set.md b/content/post/2017/06-05_postgis-backend-is-already-set.md
index a05c694..e6001a3 100644
--- a/content/post/2017/06-05_postgis-backend-is-already-set.md
+++ b/content/post/2017/06-05_postgis-backend-is-already-set.md
@@ -89,22 +89,23 @@ ORDER BY probin;
 ```
 
 In a good, install, you should have only one row that looks something like
-this.  Your version number might be different.
-
-
-	|   probin            | count |
-	|---------------------|-------|
-	|$libdir/postgis-2.4  |   446 |
+this.  Your version number might be different and count might be different.
 
+```
+|   probin            | count |
+|---------------------|-------|
+|$libdir/postgis-2.4  |   446 |
 
+```
 
 If you have more than one row, such as:
 
-| probin               | count
+```
+| probin             | count
 ---------------------+-------
- $libdir/postgis-2.4 |   446
-  $libdir/postgis-2.1 |   4
-(1 row)
+$libdir/postgis-2.4  |   446
+$libdir/postgis-2.1  |   4
+```
 
 
 
diff --git a/content/post/2022/08-25_tip-upgrading-postgis-sfcgal.md b/content/post/2022/08-25_tip-upgrading-postgis-sfcgal.md
new file mode 100644
index 0000000..25b2273
--- /dev/null
+++ b/content/post/2022/08-25_tip-upgrading-postgis-sfcgal.md
@@ -0,0 +1,73 @@
+---
+title: Upgrading postgis_sfcgal to 3.1 or higher
+slug: tip-upgrading-postgis-sfcgal
+layout: post
+category: tips
+tags: [newbie, upgrade]
+author: Regina Obe
+thumbnail:
+date: "2022-08-25"
+---
+
+As of PostGIS 3.1, the PostGIS sfcgal support library is no longer part of the
+`postgis` core library, but instead spun off into a new library `postgis_sfcgal-3`.
+
+This change is not an issue for people doing regular, soft-upgrades from a PostGIS < 3.1 compiled with SFCGAL
+to a PostGIS >= 3.1 with SFCGAL
+using `ALTER EXTENSION postgis_sfcgal UPDATE;` or `SELECT postgis_extensions_upgrade();`.
+However if you are using `pg_upgrade`, you might get errors like `postgis-3` does not contain function `postgis_sfcgal_version()` (which is part of the `postgis_sfcgal` extension).
+
+
+The three main reasons for this break were:
+
+* We wanted `postgis-3` library to have the same exposed functions regardless if you are compiling with SFCGAL or not.
+  This change was planned in PostGIS 3.0, but only the backend switching plumbing was removed and not the complete detachment.
+
+* It makes it possible for packagers to offer `postgis_sfcgal` (perhaps as a separate package),
+  without requiring other users who just want `postgis` to have to have `boost` and `CGAL`.
+
+* In the past `postgis_sfcgal` and `postgis` extensions were hooked together at the hip in the same underlying library, because their were a few functions overlapping
+  in name such as `ST_3DIntersects` and `ST_Intersects`.  Trying to explain to people how this whole thing worked, to switch the backend to sfcgal if they wanted extended 3D functionality, not to mention the added annoyance  [GUC backend of notices during upgrade](/2017/06/05/causes-for-postgis.backend-is-already-set) was more of a pain than it was worth.
+  So moving forward, we will not be reusing function names between the two extensions, and will have only non-overlapping function names.
+
+<!--more-->
+
+## Option 1
+The easiest fix when using `pg_upgrade` to upgrade PostGIS < 3.1 `postgis_sfcgal` is to first drop the `postgis_sfcgal` extension before running `pg_upgrade`.
+
+This can be done without data loss because the `postgis_sfcgal` extension only contains functions and no datatypes.
+After you have dropped it in your old cluster with:
+
+In old cluster before attempting `pg_upgrade`
+```postgres
+-- this step only needed for PostGIS < 3.1.0
+DROP EXTENSION postgis_sfcgal;
+```
+The above `DROP EXTENSION` will fail if you have views. SQL functions, or constraints bound to `postgis_sfcgal` functions.
+In those cases, you can either drop those dependencies too prior to `pg_upgrade` and make sure you have the code to recreate.
+Alternatively you can instead do *[Option 2](#option-2)*.
+
+After you have dropped the extension in your old cluster, you can then run `pg_upgrade`.
+
+After `pg_upgrade`, then in the new cluster, readd it back.
+
+
+```postgres
+CREATE EXTENSION postgis_sfcgal;
+```
+
+The create extension should error out if you don't install in the same schema as `postgis` extension.
+If you get an error, then specify the schema you installed postgis in expplicitly:
+
+ ```postgres
+CREATE EXTENSION postgis_sfcgal SCHEMA postgis;
+```
+
+## Option 2
+On old cluster, make sure you have installed postgis binaries for 3.1 or higher, then do:
+```postgres
+ALTER EXTENSION postgis UPDATE;
+SELECT postgis_extensions_upgrade();
+```
+
+Then run `pg_upgrade` as usual.
\ No newline at end of file

-----------------------------------------------------------------------

Summary of changes:
 .../2017/06-05_postgis-backend-is-already-set.md   | 21 ++++---
 .../2022/08-25_tip-upgrading-postgis-sfcgal.md     | 73 ++++++++++++++++++++++
 2 files changed, 84 insertions(+), 10 deletions(-)
 create mode 100644 content/post/2022/08-25_tip-upgrading-postgis-sfcgal.md


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