I think one thing that is contributing to this a lot too is the general issue of the tests taking up a lot of file descriptors (10k+ if I run them on a standard Debian machine).
There are a few suits that contribute to this in particular like `org.apache.spark.ExecutorAllocationManagerSuite` which, like a few others, appears to consume a lot of fds.

Wouldn't it make sense to open JIRAs about those and actively try to reduce the resource consumption of these tests? 
Seems to me these can cause a lot of unpredictable behavior (making the reason for flaky tests hard to identify especially when there's timeouts etc. involved) + they make it prohibitively expensive for many to test locally imo.

On Wed, Feb 15, 2017 at 9:24 PM, Saikat Kanjilal <sxk1969@hotmail.com> wrote:

I was working on something to address this a while ago https://issues.apache.org/jira/browse/SPARK-9487 but the difficulty in testing locally made things a lot more complicated to fix for each of the unit tests, should we resurface this JIRA again, I would whole heartedly agree with the flakiness assessment of the unit tests.

In Python we use `local[4]` for unit tests, while in Scala/Java we use `local[2]` and `local` for some unit tests in SQL, MLLib, and other components. If the ...

From: Kay Ousterhout <kayousterhout@gmail.com>
Sent: Wednesday, February 15, 2017 12:10 PM
To: dev@spark.apache.org
Subject: File JIRAs for all flaky test failures
Hi all,

I've noticed the Spark tests getting increasingly flaky -- it seems more common than not now that the tests need to be re-run at least once on PRs before they pass.  This is both annoying and problematic because it makes it harder to tell when a PR is introducing new flakiness.

To try to clean this up, I'd propose filing a JIRA *every time* Jenkins fails on a PR (for a reason unrelated to the PR).  Just provide a quick description of the failure -- e.g., "Flaky test: DagSchedulerSuite" or "Tests failed because 250m timeout expired", a link to the failed build, and include the "Tests" component.  If there's already a JIRA for the issue, just comment with a link to the latest failure.  I know folks don't always have time to track down why a test failed, but this it at least helpful to someone else who, later on, is trying to diagnose when the issue started to find the problematic code / test.

If this seems like too high overhead, feel free to suggest alternative ways to make the tests less flaky!