Update importing-postgres.md with individual DB and repeat-import information (#1437)

* Update importing-postgres.md

Additional deatails, mostly on repeating import. Structure troubleshouting section.

* Update importing-postgres.md

removing -K

* Fix path typo

Co-authored-by: Slavi Pantaleev <slavi@devture.com>

docs/importing-postgres.md

@@ -13,6 +13,7 @@ If your database name differs, be sure to change `matrix_synapse_database_databa
 The playbook supports importing Postgres dump files in **text** (e.g. `pg_dump > dump.sql`) or **gzipped** formats (e.g. `pg_dump | gzip -c > dump.sql.gz`).
 
 Importing multiple databases (as dumped by `pg_dumpall`) is also supported.  
+But the migration might be a good moment, to "reset" a not properly working bridge. Be aware, that it might affect all users (new link to bridge, new roomes, ...)
 
 Before doing the actual import, **you need to upload your Postgres dump file to the server** (any path is okay).
 
@@ -32,6 +33,7 @@ ansible-playbook -i inventory/hosts setup.yml \
 
 ## Troubleshooting
 
+### Table Ownership
 A table ownership issue can occur if you are importing from a Synapse installation which was both:
 
  - migrated from SQLite to Postgres, and
@@ -71,6 +73,8 @@ Note that if the previous import failed with an error it may have made changes w
 ERROR:  relation \"access_tokens\" already exists
 ```
 
+### Repeat import
+
 In this case you can use the command suggested in the import task to clear the database before retrying the import:
 
 ```Shell
@@ -79,4 +83,20 @@ In this case you can use the command suggested in the import task to clear the d
 # systemctl start matrix-postgres
 ```
 
+Now on your local machine run `ansible-playbook -i inventory/hosts setup.yml --tags=setup-postgres` to prepare the database roles etc.
+
+If not, you probably get this error. `synapse` is the correct table owner, but the role is missing in database.
+```
+"ERROR:  role synapse does not exist"
+```
+
 Once the database is clear and the ownership of the tables has been fixed in the SQL file, the import task should succeed.  
+Check, if `--dbname` is set to `synapse` (not `matrix`) and replace paths (or even better, copy this line from your terminal)
+
+```
+/usr/bin/env docker run --rm --name matrix-postgres-import --log-driver=none --user=998:1001 --cap-drop=ALL --network=matrix --env-file=/matrix/postgres/env-postgres-psql --mount type=bind,src=/migration/synapse_dump.sql,dst=/synapse_dump.sql,ro --entrypoint=/bin/sh docker.io/postgres:14.1-alpine -c "cat /synapse_dump.sql | grep -vE '^(CREATE|ALTER) ROLE (matrix)(;| WITH)' | grep -vE '^CREATE DATABASE (matrix)\s' | psql -v ON_ERROR_STOP=1 -h matrix-postgres --dbname=synapse"
+```
+
+### Hints
+
+To open psql terminal run `/usr/local/bin/matrix-postgres-cli`