GitHub user wzhfy opened a pull request:
https://github.com/apache/spark/pull/16696
[SPARK-19350] [SQL] Cardinality estimation of Limit and Sample
## What changes were proposed in this pull request?
Before this pr, LocalLimit/GlobalLimit/Sample propagates the same row count
and column stats from its child, which is incorrect.
We can get the correct rowCount in Statistics for Limit/Sample whether cbo
is enabled or not. Column stats should not be propagated because we don't know
the distribution of columns after Limit or Sample.
## How was this patch tested?
Added test cases.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/wzhfy/spark limitEstimation
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/16696.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 #16696
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commit 62013f5c5bc1a6d43e1b111aa3784b4524c8fda4
Author: wangzhenhua <wangzhen...@huawei.com>
Date: 2017-01-25T01:00:08Z
limit and sample estimation
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