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.
pglogical 2 is open source
EDB maintains pglogical as a service to the PostgreSQL community. For license and copyright information, or for access to the source, visit the project page at https://github.com/2ndQuadrant/pglogical
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.
Deprecation notice
v18 will be the final release for which EDB supports pglogical2. This will allow customers time to transition before v19, where we recommend using the native logical replication capabilities.