matrix-docker-ansible-deploy/docs/importing-postgres.md

Importing an existing Postgres database from another installation (optional)

Run this if you'd like to import your database from a previous installation. (don't forget to import your Synapse media_store files as well - see the importing-synape-media-store guide).

Prerequisites

For this to work, the database name in Postgres must match what this playbook uses. This playbook uses a Postgres database name of homeserver by default (controlled by the matrix_postgres_db_name variable). If your database name differs, be sure to change matrix_postgres_db_name to your desired name and to re-run the playbook before proceeding.

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.

Before doing the actual import, you need to upload your Postgres dump file to the server (any path is okay).

Importing

To import, run this command (make sure to replace <server-path-to-postgres-dump.sql> with a file path on your server):

ansible-playbook -i inventory/hosts setup.yml --extra-vars='server_path_postgres_dump=<server-path-to-postgres-dump.sql>' --tags=import-postgres

Note: <server-path-to-postgres-dump.sql> must be a file path to a Postgres dump file on the server (not on your local machine!).

Troubleshooting

A table ownership issue can occur if you are importing from a Synapse installation which was both:

• migrated from SQLite to Postgres, and
• used a username other than 'synapse'

In this case you may run into the following error during the import task:

"ERROR:  role \"synapse_user\" does not exist"

where synapse_user is the database username from the previous Synapse installation.

This can be verified by examining the dump for ALTER TABLE statements which set OWNER TO that username:

$ grep "ALTER TABLE" homeserver.sql"
ALTER TABLE public.access_tokens OWNER TO synapse_user;
ALTER TABLE public.account_data OWNER TO synapse_user;
ALTER TABLE public.account_data_max_stream_id OWNER TO synapse_user;
ALTER TABLE public.account_validity OWNER TO synapse_user;
ALTER TABLE public.application_services_state OWNER TO synapse_user;
...

It can be worked around by changing the username to synapse, for example by using sed:

$ sed -i "s/synapse_user/synapse/g" homeserver.sql"

This uses sed to perform an 'in-place' (-i) replacement globally (/g), searching for synapse user and replacing with synapse (s/synapse_user/synapse). If your database username was different, change synapse_user to that username instead.

Note that if the previous import failed with an error it may have made changes which are incompatible with re-running the import task right away; if you do so it may fail with an error such as:

ERROR:  relation \"access_tokens\" already exists

In this case you can use the command suggested in the import task to clear the database before retrying the import:

# systemctl stop matrix-postgres
# rm -rf /matrix/postgres/data/*
# systemctl start matrix-postgres

Once the database is clear and the ownership of the tables has been fixed in the SQL file, the import task should succeed.