viirya opened a new pull request, #69:
URL: https://github.com/apache/arrow-datafusion-comet/pull/69
## Which issue does this PR close?
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## Rationale for this change
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Comet native execution's scan is not started from native but from JVM. Thus
Comet scan is push-based instead of pull-based. Although we pull next input
batches from child operator in JVM, this new input is not pulled from native
but pushed from JVM side.
For an operator like Expand, one input batch can produces multiple output
batches. So we cannot pull next batch directly and push into native without
peeking it. We need to "peek" into native side and see if any more output batch
there. If so, we take it as next output, if not, we pull next input batch and
push into native side to execute on it.
If we pull next input from child operator and push it into native without
peek, new input will be ignored.
Not only we cannot have consistent way to get input for native operators.
The code of input/output to native execution is harder to understand because we
mix push-based and pull-based processing modes. This patch tries to make native
execution fully pull-based.
## What changes are included in this PR?
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