[Spivak]

> what we can deterministically show is data loss on apache kafka with no fsync() [shouldn't be a surprise to anyone] - stay tuned for an update here.

Confluent themselves can show this, the part I'm curious about is whether you can show data loss outside of the known documented failure modes. Because I, as any can anyone, show data loss by running a cluster without fsync and simultaneously pulling the plug on every server.

[insanitybit]

> Because I, as any can anyone, show data loss by running a cluster without fsync and simultaneously pulling the plug on every server.

Woah, yeah that's a serious problem. Data loss under that scenario is nothing to sneeze at.

[spenczar5]

Then enable fsync. I don't really see a way around requiring synchronization to persistent disk if you want persistence cross power outages, right?

[insanitybit]

Yes, that is what the linked benchmarks discuss...

[threeseed]

It's not a serious problem for most deployments though.

You should be running Kafka in multiple DCs/AZs for high availability and scalability.

And in that scenario fsync is nice but not necessary.

[Spivak]

I suppose but that's the trade-off for performance. You have to design your system so that can't happen. Which if you're cloud then it's deploying multi-az, if you're coloing then paying for racks with separate power and/or having battery so you have time to fsync and shut down and if you're fully on-prem then you don't need my advice.

Or I suppose just pay for a managed service from someone who does that for you.

[datadeft]

I am not entirely sure what is the reason to make Kafka transactional. The original goal was to have a message queue that holds statistical data where the data loss cannot significantly alter the outcome of the analytics performed on the (often incomplete) data. Why are in this argument about fsync and such now? Did something change?

If you need reliable data storage do not use Kafka or similar technologies.

[ako]

Do you have a source/link for that original goal? I wasn’t aware of this, and as such expect that I can rely on kafka for my events. Also, if this is really the case it should be mentioned on the homepage of Kafka.

Just checked kafka’s homepage, it mentions mission critical, durable, fault tolerant, stores data safely, zero message loss, trusted… Seems they’ve moved on from their original goal.

[datadeft]

"The original use case for Kafka was to be able to rebuild a user activity tracking pipeline as a set of real-time publish-subscribe feeds. This means site activity (page views, searches, or other actions users may take) is published to central topics with one topic per activity type."

https://kafka.apache.org/

[skrtskrt]

Kafka is used widely as a persistent event store, and its development features reflect that.

Why would I not just turn on fsync or deploy in a distributed pattern for reliability so I can just continue using it instead of ripping it out, benchmarking something new, teaching the entire org something new, potentially negotiating a new contract, and then executing a huge migration?

[datadeft]

Just like heroin is widely used a recreational drug. We live in a free world and you can use Kafka as a persistent reliable store, even use it transactionally.

Instead of reading the marketing claims I like to read what @aphyr has to say about data storage systems.

https://aphyr.com/posts/293-call-me-maybe-kafka

[relay23]

Also https://jepsen.io/analyses/redpanda-21.10.1

[relay23]

Are you sure performance would be acceptable if you just turned on fsync on every message?

[skrtskrt]

well it obviously depends on your usage patterns.

But at a certain point any technology is going to reach the limits of what current hardware and operating system primitives can do.

fsync vs. distributed consensus vs. other tradeoffs w.r.t reliability and consistency are not inherent to "Kafka or similar technologies". It's inherent to anything that runs on a computer in the real world.

Generally unless your scale is mind-bogglingly big, the ROI on tuning what you already have is going to be way way bigger than just ripping it out because you read a benchmarking article.

[tyingq]

>The original goal was to have a message queue that holds statistical data

I suppose that might have been the original goal, but the current tag line includes "data integration" and "mission-critical".

"Apache Kafka is an open-source distributed event streaming platform used by thousands of companies for high-performance data pipelines, streaming analytics, data integration, and mission-critical applications."

[datadeft]

I guess you can add any feature to anything. I think this whole investor driven development is just sad.