Cleaning Up My Closet AKA Synapse

I’ve been running a self-hosted Matrix installation with the Synapse homeserver, which includes a variety of integrations from Signal to IRC with Heisenbridge.

Over time, the number of rooms and chats can really add up, along with the disk space used by events in the PostgreSQL database. This led me to look for a way to purge the history of channels and free up space in my database.

Thankfully, the Synapse server provides an open API that allows for history purging via a simple curl command:

TIMESTAMP=$(($(date -d "-1 year" +%s) * 1000)) # 1 year ago
curl -H "Authorization: Bearer $TOKEN" "http://localhost:8008/_synapse/admin/v1/purge_history/$room" -X POST -d "{\"purge_up_to_ts\":$TIMESTAMP,\"delete_local_events\":true}"

You’ll need an admin token, which you can obtain from your user account in the Element web app (assuming you are an admin).

Next, we need a list of rooms. The API can assist with this as well:

curl -H "Authorization: Bearer $TOKEN" "http://localhost:8008/_synapse/admin/v1/rooms?limit=1000" > roomlist.json

To prepare for the purge, we’ll clean up the roomlist.json and encode the room IDs:

cat roomlist.json | jq '.rooms[] | .room_id' -r | sed 's/\!/%21/g' > to_purge.txt

Now, let’s execute the purge_history API call for all the rooms:

TIMESTAMP=$(($(date -d "-1 year" +%s) * 1000)) # 1 year ago
while read room; do
  curl -H "Authorization: Bearer $TOKEN" "http://localhost:8008/_synapse/admin/v1/purge_history/$room" -X POST -d "{\"purge_up_to_ts\":$TIMESTAMP,\"delete_local_events\":true}"
done < to_purge.txt

This process will remove all events older than one year.

It might take a while, but don’t forget to run a VACUUM FULL; on your database afterward to reclaim the space.

I managed to reclaim about 40GiB of space: