GitHub user kiszk opened a pull request:
https://github.com/apache/spark/pull/18002
[SPARK-20770][SQL] Improve ColumnStats
## What changes were proposed in this pull request?
This PR improves the implementation of `ColumnStats` by using the following
appoaches.
1. Declare subclasses of `ColumnStats` as `final`
2. Remove unnecessary call of `row.isNullAt(ordinal)`
3. Remove the dependency on `GenericInternalRow`
For 1., this declaration encourages method inlining and other optimizations
of JIT compiler
For 2., in `gatherStats()`, while previous code in subclasses of
`ColumnStats` always calls `row.isNullAt()` twice, the PR just calls
`row.isNullAt()` only once.
For 3., `collectedStatistics()` returns `Array[Any]` instead of
`GenericInternalRow`. This removes the dependency of unnecessary package and
reduces the number of allocations of `GenericInternalRow`.
In addition to that, in the future, `gatherValueStats()`, which is
specialized for each data type, can be effectively called from the generated
code without using generic data structure `InternalRow`.
## How was this patch tested?
Tested by existing test suite
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/kiszk/spark SPARK-20770
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/18002.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 #18002
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