We are currently testing PostgreSQL 11's built-in logical replication. We are trying to initialize a subscriber (from scratch) from a publisher with a large database (+6TB) with around 220 tables.
We tweaked the configuration parameters below, both on publisher and subscriber, in order to minimize the initial copy data phase delay:
- max_replication_slots
- max_wal_senders
- max_wal_size
- max_worker_processes
- max_logical_replication_workers
- max_sync_workers_per_subscription
- max_worker_processes
The two PostgreSQL instances are using the same hardware: 48 vCPU, 384 GB ram, 10GB network and same version of software (PostgreSQL 11.6).
We pre-loaded the full schema of the database (with indexes and constraints) on the subscriber since it's mandatory to have the logical replication working.
However, the initial copy data phase is quite long (+2 days and still running) for largest tables in the database. There is no load on the publisher since it's a staging environment.
We noticed that logical replication workers processes on the subscriber can reach more than 90% CPU usage per worker.
We understand that we cannot have more than one worker per table running but we would like to know if there is anything that could help us to achieve this initial copy phase more quickly.
We tried another solution: we loaded a minimal schema (without indexes and constraints) on the subscriber and created the subscription. The initial copy phase was way faster (a few hours). Then we created indexes and constraints. Is this a suitable solution for production? Will the logical replication flow be buffered by the replication slots during index creation and get in sync afterwards or will it conflict due to locking issues?