GitHub user cloud-fan opened a pull request:
https://github.com/apache/spark/pull/23265
[2.4][SPARK-26021][SQL][FOLLOWUP] only deal with NaN and -0.0 in
UnsafeWriter
backport https://github.com/apache/spark/pull/23239 to 2.4
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## What changes were proposed in this pull request?
A followup of https://github.com/apache/spark/pull/23043
There are 4 places we need to deal with NaN and -0.0:
1. comparison expressions. `-0.0` and `0.0` should be treated as same.
Different NaNs should be treated as same.
2. Join keys. `-0.0` and `0.0` should be treated as same. Different NaNs
should be treated as same.
3. grouping keys. `-0.0` and `0.0` should be assigned to the same group.
Different NaNs should be assigned to the same group.
4. window partition keys. `-0.0` and `0.0` should be treated as same.
Different NaNs should be treated as same.
The case 1 is OK. Our comparison already handles NaN and -0.0, and for
struct/array/map, we will recursively compare the fields/elements.
Case 2, 3 and 4 are problematic, as they compare `UnsafeRow` binary
directly, and different NaNs have different binary representation, and the same
thing happens for -0.0 and 0.0.
To fix it, a simple solution is: normalize float/double when building
unsafe data (`UnsafeRow`, `UnsafeArrayData`, `UnsafeMapData`). Then we don't
need to worry about it anymore.
Following this direction, this PR moves the handling of NaN and -0.0 from
`Platform` to `UnsafeWriter`, so that places like `UnsafeRow.setFloat` will not
handle them, which reduces the perf overhead. It's also easier to add comments
explaining why we do it in `UnsafeWriter`.
## How was this patch tested?
existing tests
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/cloud-fan/spark minor
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/23265.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 #23265
commit 6a837c019eaf7bc9907715a54778bfbb339f3342
Author: Wenchen Fan
Date: 2018-12-08T19:18:09Z
[SPARK-26021][SQL][FOLLOWUP] only deal with NaN and -0.0 in UnsafeWriter
A followup of https://github.com/apache/spark/pull/23043
There are 4 places we need to deal with NaN and -0.0:
1. comparison expressions. `-0.0` and `0.0` should be treated as same.
Different NaNs should be treated as same.
2. Join keys. `-0.0` and `0.0` should be treated as same. Different NaNs
should be treated as same.
3. grouping keys. `-0.0` and `0.0` should be assigned to the same group.
Different NaNs should be assigned to the same group.
4. window partition keys. `-0.0` and `0.0` should be treated as same.
Different NaNs should be treated as same.
The case 1 is OK. Our comparison already handles NaN and -0.0, and for
struct/array/map, we will recursively compare the fields/elements.
Case 2, 3 and 4 are problematic, as they compare `UnsafeRow` binary
directly, and different NaNs have different binary representation, and the same
thing happens for -0.0 and 0.0.
To fix it, a simple solution is: normalize float/double when building
unsafe data (`UnsafeRow`, `UnsafeArrayData`, `UnsafeMapData`). Then we don't
need to worry about it anymore.
Following this direction, this PR moves the handling of NaN and -0.0 from
`Platform` to `UnsafeWriter`, so that places like `UnsafeRow.setFloat` will not
handle them, which reduces the perf overhead. It's also easier to add comments
explaining why we do it in `UnsafeWriter`.
existing tests
Closes #23239 from cloud-fan/minor.
Authored-by: Wenchen Fan
Signed-off-by: Dongjoon Hyun
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