GitHub user uncleGen opened a pull request:
https://github.com/apache/spark/pull/17141
[SPARK-19800][SS][WIP] Implement one kind of streaming sampling - reservoir
sampling
## What changes were proposed in this pull request?
This pr adds a special streaming sample operator to support `sample`. It
add a new evolving operator `reservoir`, and introduce new logical plan
`ReservoirSample` and two physical plan `StreamingReservoirSampleExec` and
`ReservoirSampleExec`.
The following cases are supported:
- batch table reservoir sampling
- stream table reservoir sampling with/without aggregation and watermark in
Update/Complete output mode
Not supported cases:
- reservoir sampling in Append output mode
Followups:
- move `reservoir` into `sample` operator
## How was this patch tested?
add new unit tests.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/uncleGen/spark sampling
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/17141.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #17141
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