gianm commented on a change in pull request #8644: Fix Kinesis resharding issues
URL: https://github.com/apache/incubator-druid/pull/8644#discussion_r332836956
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File path:
extensions-core/kinesis-indexing-service/src/main/java/org/apache/druid/indexing/kinesis/supervisor/KinesisSupervisor.java
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@@ -212,14 +225,47 @@ protected void
scheduleReporting(ScheduledExecutorService reportingExec)
// not yet implemented, see issue #6739
}
+
+ /**
+ * We try to parse the shard number of the shard ID, using a BigInteger
because the Kinesis shard ID can be
+ * up to 128 characters. The shard number is used preferentially because it
provides a fixed and easily predictable
+ * mapping from shard to task group number.
+ *
+ * If we can't parse the shard number from the ID, then we fall back to
hashing the shard ID string.
Review comment:
I don't think it can happen today, given how Kinesis names shards. It might
happen in the future if they change the format of a shard identifier for some
reason. I don't think that's likely to happen, since it would probably break a
ton of stuff so Amazon would hesitate to do it. So just doing the BigInteger
path only (and throwing an exception if they can't be parsed for some reason)
is a risk but a small one. On the other hand it's zero risk to treat them as
opaque strings.
I read the code in the PR as trying to have it both ways, a 'nice' behavior
(assign shards round-robin based on shard number) but also zero risk of Amazon
doing an unexpected change and breaking us.
Fwiw I think if I was writing the patch then I would go with using the zero
risk SHA path only — it would mean shard assignment that isn't as
human-predictable, but it shortens up the code while still avoiding
forward-compatibility risk, which seems worth it to me.
In the end I am inclined to leave it up to the author @jon-wei.
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