Understanding conflict resolution and avoidance in PostgreSQL: a complete guide

Summary

The PGDay Chicago 2025 Postgres conference has come and gone, and so too has my presentation on conflict management in Postgres Multi-Master clusters. For those who couldn’t attend this year, there’s no need to fret, as this blog will present all of the relevant details. By the end, you'll be well armed with the knowledge necessary to identify, mitigate, and avoid the worst scenarios which may arise in a distributed Postgres cluster.Is Bi-Directional Logical Replication Implicitly Safe?The release announcement for Postgres 16 included this cryptic note:Finally, this release begins adding support for bidirectional logical replication, introducing functionality to replicate data between two tables from different publishers.Despite how that may sound on the surface, that shouldn’t be interpreted as tacit permission or a resounding recommendation to immediately spin up an Active-Active logical replication cluster using native Postgres logical replication. Among other things, there are novel sequence rules, data merging concerns, conflict management, and the dreaded potential of node divergence.None of these situations are managed by default, and a problem related to any one of these issues could result in implicit or explicit data loss. Consider a cluster distributed to three distinct geographic regions:What might happen if Bob is in Ashburn, Virginia, and opens an account at ACME using his email address [email protected]? Probably nothing. Unless perhaps his wife is on vacation in Frankfurt, Germany and happens to be touring the ACME global office and decides to sign Bob up for an account because she knows he’s been meaning to do so. Through some providence of fate, this happens within the round-trip latency between Frankfurt and Ashburn, and now we have a problem. Which set of account credentials and related information do we retain?The answer to that question is why we’re here, and why solutions like pgEdge are necessary to successfully navigate the perilous seas of ...