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https://issues.apache.org/jira/browse/SPARK-6962?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14498806#comment-14498806
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Patrick Wendell commented on SPARK-6962:
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[~adav] One thing that could cause this is if a single node is doing GC
thrashing or is otherwise hung up, but the transport cannot detect that
anything is wrong with that node. IIRC we've seen similar things in the past
even with the old transport and we had to add various timeouts to make sure
that the receive side didn't ever wait indefinitely.
> Netty BlockTransferService hangs in the middle of SQL query
> -----------------------------------------------------------
>
> Key: SPARK-6962
> URL: https://issues.apache.org/jira/browse/SPARK-6962
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Affects Versions: 1.2.0, 1.2.1, 1.3.0
> Reporter: Jon Chase
> Attachments: jstacks.txt
>
>
> Spark SQL queries (though this seems to be a Spark Core issue - I'm just
> using queries in the REPL to surface this, so I mention Spark SQL) hang
> indefinitely under certain (not totally understood) circumstances.
> This is resolved by setting spark.shuffle.blockTransferService=nio, which
> seems to point to netty as the issue. Netty was set as the default for the
> block transport layer in 1.2.0, which is when this issue started. Setting
> the service to nio allows queries to complete normally.
> I do not see this problem when running queries over smaller (~20 5MB files)
> datasets. When I increase the scope to include more data (several hundred
> ~5MB files), the queries will get through several steps but eventuall hang
> indefinitely.
> Here's the email chain regarding this issue, including stack traces:
> http://mail-archives.apache.org/mod_mbox/spark-user/201503.mbox/<cae61spfqt2y7d5vqzomzz2dmr-jx2c2zggcyky40npkjjx4...@mail.gmail.com>
> For context, here's the announcement regarding the block transfer service
> change:
> http://mail-archives.apache.org/mod_mbox/spark-dev/201411.mbox/<cabpqxssl04q+rbltp-d8w+z3atn+g-um6gmdgdnh-hzcvd-...@mail.gmail.com>
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