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Show HN: Open source, logical multi-master PostgreSQL replication

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131 points pgedge_postgres | 2 comments | 09 Oct 25 22:53 UTC | HN request time: 0s | source
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pisikesipelgas ◴[10 Oct 25 05:01 UTC] No.45535502[source]▶
Hi, How do You guys resolve the application database DDL issue when multimaster is in use? One node gets updated, DDL is will be replicated (?) to second node, which is used by not-jet-updated application which is not compatible with updated database structure. This problem has bugged me for a while. And second and similar issue with most replication setups is let's take for postgis for example. Again in one node this extension gets updated. Now what? Data will be replicated to node which is not jet updated and cause whole system to be not functional.
replies(1): >>45535665 #
baq ◴[10 Oct 25 05:44 UTC] No.45535665[source]▶
It’s an engineering problem: you have to design the system so that it remains functional in this exact scenario - it follows that the system isn’t just code and build artifacts, but also its deployment processes.
replies(1): >>45535711 #
pisikesipelgas ◴[10 Oct 25 05:54 UTC] No.45535711[source]▶
Hi, Thanks for the reply. This is what i figured too. So there is essentially no way to achieve this without service downtime when using application which is not written to handle those kind of situations (eg. 3rd party things).
replies(1): >>45535911 #
1. baq ◴[10 Oct 25 06:32 UTC] No.45535911[source]▶
Again an engineering problem. You can deploy with zero downtime and people have been doing this for decades. It takes infrastructure like load balancers, ability to run versions in parallel and runtime support for feature flags, but it’s absolutely doable and ultimately just another day in the office for anyone with global operations. A lot of 3rd party tools actually support these workflows for this exact reason.
replies(1): >>45536366 #
2. qaq ◴[10 Oct 25 07:57 UTC] No.45536366[source]▶
You gonna pause writes for cutover so while not downtime, specifically for postgres load balancers, ability to run versions in parallel not gonna help you there.