PGConf.Online 2021

What's next in Logical Replication?

Logical replication has been there since 10.0 and with each release, it is getting better. This talk will start with the basic architecture of Logical replication in PostgreSQL and then cover the various ways in which it can be helpful to users.

One of the shortcomings of logical replication as compare to physical replication is that currently, it allows the transaction to be replicated only once it is committed. This can create a large apply lag on the subscriber side for long-running transactions. We will discuss the solution implemented for this problem for PostgreSQL.

We will also discuss the other major work being done in logical replication which is to allow the streaming of transactions at the prepare time. This will help us in implementing conflict-free logical replication. This can be used for scaling-out reads as well. Because of 2PC, we can ensure that on subscribers we have all the data committed on the master. Now, we can design a system where different nodes are owners of some set of tables and we can always get the data of those tables reliably from those nodes, and then one can have some external process that will route the reads accordingly.

In the end, this will cover the new enhancements, improvements related to Logical Replication in recent PostgreSQL releases.

How many engineers does it take to make subscripting work?

Recently landed in PostgreSQL, jsonb subscripting support doesn't look as exciting as some other improvements around jsonb. But it's user visible changes are only tip of the iceberg. How many people were involved to make it, and what decisions choices were made? How long did it take, and what are the good/bad ideas to promote a patch? These and few other questions will be our targets in this talk.

Consensus, Postgres, Multimaster

Postgres Pro Multimaster is Postgres extension (and a set of core patches) providing high availability (HA) with strong consistency and read scalability. It forms symmetric shared-nothing cluster synchronously replicating the data and automatically performing disaster recovery. During the last year we've put significant efforts ensuring and proving that consistency is preserved in all scenarios. The new version, which will be released as part of Postgres Pro Enterprise 13 uses Paxos algorithm for determining transaction outcome and custom protocol governing the recovery process; we used TLA+ model checker to verify its correctness. I'll tell how these things work and why in some cases multimaster may be an attractive alternative to the traditional streaming replication based HA deployments.

multimaster is now open source, available at https://github.com/postgrespro/mmts

To make the talk less narrow specialized and more appealing to the wide audience, in the first part I will shed some light on how generally modern DBMSs (mostly so-called NewSQL) handle fault tolerance. In particular,

• what is a strongly consistent DBMS and the associated overhead;
• what is distributed consensus, Paxos, Raft;
• how they help here;

I won't do an attempt to explain any algorithms line-by-line; it would be hardly useful given the time frames and there is a lot of literature available anyway. The goal is rather to waymark the field and get you a bit comfortable there.

PostgreSQL partitioning. Work In Progress

Native partitioning was introduced in PostgreSQL 10, and every new release comes with more features and optimizations to this area. Yet, there is still room for improvement.

This talk briefly compares the built-in PostgreSQL partitioning with third-party extensions (pg_pathman and pg_partman), to understand what we still don't have in the core. This talk also includes an overview of partitioning-related features that are currently being developed and aimed for PostgreSQL 14.