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Comment by Misdicorl | Hacker News Reader

I suppose it depends on your message volume. To me, processing 100k messages and then getting a page however long later as the broker (or whatever) falls apart sounds much worse than head of line blocking and seeing the problem directly in my consumer. If I need to not do head of line blocking, I can build whatever failsafe mechanisms I need for the problematic data and defer to some other queueing system (typically, just add an attempt counter and replay the message to the same kafka topic and then if attempts > X, send it off to wherever)

I'd rather debug a worker problem than an infra scaling problem every day of the week and twice on Sundays.

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It's interesting you say that, since this turned an infra scaling problem into a worker problem for us. Previously, we would get terrible head-of-line throughput issues, so we would use an egregious number of partitions to try to alleviate that. Lots of partitions is hard to manage since resizing topics is operationally tedious and it puts a lot of strain on brokers. But no matter how many partitions you have, the head-of-line still blocks. Even cases where certain keys had slightly slower throughput would clog up the whole partition with normal consumers.

The parallel consumer nearly entirely solved this problem. Only the most egregious cases where keys were ~3000 times slower than other keys would cause an issue, and then you could solve it by disabling that key for a while.

Yeah I'd say kafka is not a great technology if your median and 99ths (or 999ths if volume is large enough) are wildly different which sounds like your situation. I use kafka in contexts where 99ths going awry usually aren't key dependent so I don't have the issues you see.

I tend to prefer other queueing mechanisms in those cases, although I still work hard to make 99ths and medians align as it can still cause issues (especially for monitoring)

Follow on: If you're using kafka to publish messages to multiple consumers, this is even worse as now you're infecting every consumer with data processing issues from every other consumer. Bad juju

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