GitHub user dongjoon-hyun opened a pull request:
https://github.com/apache/spark/pull/16440
[SPARK-18857][SQL] Don't use `Iterator.duplicate` for `incrementalCollect`
in Thrift Server
## What changes were proposed in this pull request?
To support `FETCH_FIRST`, SPARK-16563 used Scala `Iterator.duplicate`.
However,
Scala `Iterator.duplicate` uses a **queue to buffer all items between both
iterators**,
this causes GC and hangs for queries with large number of rows. We should
not use this,
especially for `spark.sql.thriftServer.incrementalCollect`.
https://github.com/scala/scala/blob/2.12.x/src/library/scala/collection/Iterator.scala#L1262-L1300
## How was this patch tested?
Pass the existing tests.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/dongjoon-hyun/spark SPARK-18857
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/16440.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 #16440
----
commit 125e79c107db599b15f700c3b4023d9516b28fd1
Author: Dongjoon Hyun <[email protected]>
Date: 2016-12-30T12:38:07Z
[SPARK-18857][SQL] Don't use `Iterator.duplicate` for `incrementalCollect`
in Thrift Server.
Since Scala `Iterator.duplicate` uses a queue to buffer all items between
both iterators,
this causes GC and hangs. We should not use this, especially for
`spark.sql.thriftServer.incrementalCollect`.
https://github.com/scala/scala/blob/2.12.x/src/library/scala/collection/Iterator.scala#L1262-L1300
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