pglogical 2

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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.

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