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Comment by irfansharif | Hacker News Reader

> If I understood correctly, the extra round trip on the reader only occurs with left-over intents, which are the product of an earlier failure.

Left over intents are also visible for an ongoing txn, before those intents are resolved. But there's no added latency in the read path, I've commented elsewhere in the thread to explain how.

> After coordinator failure events, the new coordinator starts to clean up left-over intents asynchronously (nothing specific is waiting for it to finish).

The cleanup happens by readers on demand, there's no separate global coordinator scanning the keyspace and resolving old write intents.

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> Left over intents are also visible for an ongoing txn, before those intents are resolved. But there's no added latency in the read path, I've commented elsewhere in the thread to explain how.

Thanks, that was a helpful comment.

> The cleanup happens by readers on demand, there's no separate global coordinator scanning the keyspace and resolving old write intents.

Oh, that's a little surprising. I assumed the coordinator(s) did so because asynchronous cleanup is mentioned numerous times in the article, but upon closer scrutiny I see now that it only applies in the after phase of transactions without a failure.

Would that scanning, analogous to RAID "resilvering" subject to write-intent ranges to limit the keyspace regions scanned, usefully improve read latencies later?

> I see now that it only applies in the after phase of transactions without a failure.

Yep.

> Would that scanning, analogous to RAID "resilvering" subject to write-intent ranges to limit the keyspace regions scanned, usefully improve read latencies later?

I think it's just a better design to have it done on demand. The keyspace is large and failures are rare, and when one of these zombie intents are happened upon, the very first reader addressing it resolves it for all subsequent readers. A global scan would improve read latencies later, but not by much and not for many readers.

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