GitHub user HyukjinKwon opened a pull request:
https://github.com/apache/spark/pull/22697
[SPARK-25700][SQL][BRANCH-2.4] Partially revert append mode support in Data
Source V2
## What changes were proposed in this pull request?
This PR proposes to partially revert
https://github.com/apache/spark/commit/5fef6e3513d6023a837c427d183006d153c7102b
so that it does make a readsupport and read schema when it writes in branch 2-4
since it's too breaking change.
https://github.com/apache/spark/commit/5fef6e3513d6023a837c427d183006d153c7102b
happened to create a readsupport in write path, which ended up with reading
schema from readsupport at write path.
For instance, this breaks
`spark.range(1).format("source").write.save("non-existent-path")` case since
there's no way to read the schema from "non-existent-path".
See also https://github.com/apache/spark/pull/22009#discussion_r223982672
See also https://github.com/apache/spark/pull/22688
See also
http://apache-spark-developers-list.1001551.n3.nabble.com/Possible-bug-in-DatasourceV2-td25343.html
## How was this patch tested?
Unit test and manual tests.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/HyukjinKwon/spark append-revert-2.4
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/22697.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 #22697
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commit 9489ba1d684874d848d3dfa76a63aac9f2fcd717
Author: hyukjinkwon <gurwls223@...>
Date: 2018-10-11T12:33:11Z
Partially revert append mode support in Data Source V2
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