GitHub user cloud-fan opened a pull request:
https://github.com/apache/spark/pull/18955
[SPARK-21743][SQL] top-most limit should not cause memory leak
## What changes were proposed in this pull request?
For top-most limit, we will use a special operator to execute it:
`CollectLimitExec`.
`CollectLimitExec` will retrieve `n`(which is the limit) rows from each
partition of the child plan output, see
https://github.com/apache/spark/blob/v2.2.0/sql/core/src/main/scala/org/apache/spark/sql/execution/SparkPlan.scala#L311.
It's very likely that we don't exhaust the child plan output.
This is fine when whole-stage-codegen is off, as child plan will release
the resource via task completion listener. However, when whole-stage codegen is
on, the resource can only be released if all output is consumed.
To fix this memory leak, one simple approach is, when `CollectLimitExec`
retrieve `n` rows from child plan output, child plan output should only have
`n` rows, then the output is exhausted and resource is released. This can be
done by wrapping child plan with `LocalLimit`
## How was this patch tested?
a regression test
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/cloud-fan/spark leak
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/18955.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 #18955
----
commit 67ac3aa37ad7762f3d95c7e3f4900ba47124583b
Author: Wenchen Fan <wenc...@databricks.com>
Date: 2017-08-16T04:27:03Z
top-most limit should not cause memory leak
----
---
If your project is set up for it, you can reply to this email and have your
reply appear on GitHub as well. If your project does not have this feature
enabled and wishes so, or if the feature is enabled but not working, please
contact infrastructure at infrastruct...@apache.org or file a JIRA ticket
with INFRA.
---
---------------------------------------------------------------------
To unsubscribe, e-mail: reviews-unsubscr...@spark.apache.org
For additional commands, e-mail: reviews-h...@spark.apache.org
