An implementation of synchronous multi-master replication based on logical decoding and xtm.

1. Install contrib/raftable and contrib/mmts on each instance.
2. Add these required options to the postgresql.conf of each instance in the cluster.

   max_prepared_transactions = 200 # should be > 0, because all
   								# transactions are implicitly two-phase
   max_connections = 200
   max_worker_processes = 100 # at least (2 * n + p + 1)
   						   # this figure is calculated as:
   						   #   1 raftable worker
   						   #   n-1 receiver
   						   #   n-1 sender
   						   #   1 mtm-sender
   						   #   1 mtm-receiver
   						   #   p workers in the pool
   max_parallel_degree = 0
   wal_level = logical # multimaster is build on top of
   					# logical replication and will not work otherwise
   max_wal_senders = 10 # at least the number of nodes
   wal_sender_timeout = 0
   default_transaction_isolation = 'repeatable read'
   max_replication_slots = 10 # at least the number of nodes
   shared_preload_libraries = 'raftable,multimaster'
   multimaster.workers = 10
   multimaster.queue_size = 10485760 # 10mb
   multimaster.node_id = 1 # the 1-based index of the node in the cluster
   multimaster.conn_strings = 'dbname=... host=....0.0.1 port=... raftport=..., ...'
   						   # comma-separated list of connection strings
   multimaster.use_raftable = true
   multimaster.heartbeat_recv_timeout = 1000
   multimaster.heartbeat_send_timeout = 250
   multimaster.ignore_tables_without_pk = true
   multimaster.twopc_min_timeout = 2000

3. Allow replication in pg_hba.conf.

create extension mmts; to gain access to these functions:

• mtm.get_nodes_state() -- show status of nodes on cluster
• mtm.get_cluster_state() -- show whole cluster status
• mtm.get_cluster_info() -- print some debug info
• mtm.make_table_local(relation regclass) -- stop replication for a given table

• make -C contrib/mmts check to run TAP-tests.
• make -C contrib/mmts xcheck to run blockade tests. The blockade tests require docker, blockade, and some other packages installed, see requirements.txt for the list.