GitHub user cloud-fan opened a pull request:
https://github.com/apache/spark/pull/23239
[SPARK-26021][SQL][followup] only deal with NaN and -0.0 in UnsafeWriter
## 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. Range partitioner(the sorter). `-0.0` and `0.0` should be assigned to
the same partition. Different NaNs should be assigned to the same partition.
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. comparison expressions. `-0.0` and `0.0` should be treated as same.
Different NaNs should be treated as same.
The case 4 is OK. Our comparison already handles NaN and -0.0, and for
struct/array/map, we will recursively compare the fields/elements.
Case 1, 2 and 3 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: let `UnsafeProjection` always produce
`UnsafeRow`s with NaN and -0.0 normalized(use the standard NaN and replace -0.0
with 0.0). The `UnsafeRow`s in case 1, 2 and 3 are all created by
`UnsafeProjection`.
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/23239.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 #23239
----
commit 797ade3eb175c41866efbffa3cb4c30f90e49ca7
Author: Wenchen Fan <wenchen@...>
Date: 2018-12-05T15:05:39Z
only deal with NaN and -0.0 in UnsafeWriter
----
---
---------------------------------------------------------------------
To unsubscribe, e-mail: reviews-unsubscr...@spark.apache.org
For additional commands, e-mail: reviews-h...@spark.apache.org
