compress-all.rb

#!/usr/bin/env ruby

rooms = `sudo -u postgres psql synapse -t -c "select room_id from rooms;"`.split("\n")

rooms.reject! {|r| r.strip == "" }

rooms.each_with_index do |r, i|
  `./synapse-compress-state -p 'postgresql://USERNAME:PASSWORD@HOSTNAME/DBNAME' -r '#{r.strip}' -o out#{i}.sql -t`
end

Leaves you with a number of out[number].sql-files. You can apply them via sudo -u postgres psql synapse < *.sql

No warranty for any stuff you copy paste out of random gists, obviously ;)