pglogical 2

The pglogical 2 extension provides logical streaming replication for PostgreSQL, using a publish/subscribe model. It is based on technology developed as part of EDB Postgres Distributed.

We use the following terms to describe data streams between nodes, deliberately reused from the earlier Slony technology:

• Nodes - PostgreSQL database instances
• Providers and Subscribers - roles taken by Nodes
• Replication Set - a collection of tables

pglogical is utilising the latest in-core features, so we have these version restrictions:

• Provider & subscriber nodes must run PostgreSQL 9.4+
• PostgreSQL 9.5+ is required for replication origin filtering and conflict detection
• Additionally, subscriber can be Postgres-XL 9.5+

Use cases supported are:

• Upgrades between major versions (given the above restrictions)
• Full database replication
• Selective replication of sets of tables using replication sets
• Selective replication of table rows at either publisher or subscriber side (row_filter)
• Selective replication of table columns at publisher side
• Data gather/merge from multiple upstream servers

Architectural details:

• pglogical works on a per-database level, not whole server level like physical streaming replication
• One Provider may feed multiple Subscribers without incurring additional disk write overhead
• One Subscriber can merge changes from several origins and detect conflict between changes with automatic and configurable conflict resolution (some, but not all aspects required for multi-master).
• Cascading replication is implemented in the form of changeset forwarding.