gianm commented on pull request #10267:
URL: https://github.com/apache/druid/pull/10267#issuecomment-672522776
> (1) and (3) are breaking changes.
Fwiw, on this one, I think the likelihood of (1) causing problems is low.
It's a breaking change because if you were previously specifying a column as an
input to one of your dimensionsSpec or aggregators, but then explicitly _not_
including in the input source's "dimensions" or "metrics" list, it'll now
actually get read. Previously it'd be treated as null. The new behavior is
better & less brittle but is different.
(3) is still fairly low, but somewhat more likely. It's possible that
someone had their timestampSpec set to something like `{"column": "__time",
"format": "iso"}`, which is "wrong" but would have worked previously. Now it
won't work: the timestamp will fail to parse (as it should, because it's not
really in iso format).
This patch as written just lets these things break, but we could cushion the
fall, potentially:
- For (1) we could throw an error in situations where people explicitly
specify `dimensions` and `metrics` that don't match the computed inputs,
informing them that these parameters no longer have an effect and asking them
to remove them.
- For (3) we could introduce a flag that causes an error to be thrown when
you set the timestamp spec to anything other than `{"column": "__time",
"format": "auto"}` or `{"column": "__time", "format": "millis"}`. Druid would
invite you to set the flag, which would tell it "yes I really want the new,
more correct behavior". That feature flag could be on or off by default.
What do people think?
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