Postgres Storytelling: What's going on with Synchronous Replication? | POSETTE 2024

Video of a conference talk about what's going on with synchronous replication presented by Boriss Mejias at POSETTE: An Event for Postgres 2024. This is an illustrated Postgres story about Monica DeBea, a fictional talented support engineer based on real-life talented support engineers. Once upon a time Monica got a phone call at her desk at the end of the working day. She anticipated it was David again with a problem that would keep her at the office until the darkest hour. But it wasn’t David, it was Derk, the software engineer that is always walking around with a chess board, and he had a very interesting problem to discuss. Synchronous replication was extremely slow, and the only observable symptom was a huge amount of ‘SyncRep’ wait events. The network was not to be blamed, the CPU usage was smooth, and the RAM had enough space to still allocate the latest release of “Thundermother” in high resolution. So what was going on? This was a nice challenge.

In this Postgres “storytelling” talk about Monica DeBea, you will learn how synchronous replication works, how vacuum and large tables affect replication, and what you need to take into account with respect to WAL files.

Boriss is a holistic system software engineer, PostgreSQL solution architect at EDB, free software user, and headbanger. He got his PhD researching distributed self-managing systems and has been working with PostgreSQL since version 9.1. In 2018, he started the PostgreSQL User Group in Belgium. Boriss has presented in many conferences in academia, open source, and Postgres. Being a father of two fantastic daughters, he also has experience in storytelling. Now that they have grown up, he has decided to try telling stories to the Postgres community.

Chapters:
00:00 - Intro
02:35 - The problem
05:05 - Initial investigation of the problem
05:54 - Synchronous replication explained
11:10 - Why is there accumulation of sychronous replication events at a certain point
15:54 - Why were there these wait events
22:55 - The solution

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Presenters:
Boriss Mejias