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From Saikat Kanjilal <sxk1...@hotmail.com>
Subject Re: File JIRAs for all flaky test failures
Date Tue, 28 Mar 2017 16:43:15 GMT
I'm happy to help out in this effort and will look at that label and see what tests I can look
into and/or fix.


________________________________
From: Kay Ousterhout <keo@eecs.berkeley.edu>
Sent: Monday, March 27, 2017 9:47 PM
To: Reynold Xin
Cc: Saikat Kanjilal; Sean Owen; dev@spark.apache.org
Subject: Re: File JIRAs for all flaky test failures

Following up on this with a renewed plea to file JIRAs when you see flaky tests.  I did a
quick skim of the PR builder, and there were 17 times in the last week when a flaky test led
to a Jenkins failure, and someone re-ran the tests without filing (or updating) a JIRA (my
apologies to anyone who was incorrectly added here):

cloud-fan (4)
gatorsmile (4)
wzhfy (4)
holdenk (1)
kunalkhamar (1)
hyukjinkwon (1)
scrapcodes (1)
srowen (1)

Are you on this list?  It's not too late to look at the test that failed and file (or update)
the appropriate JIRA.

If you weren't convinced by my last email, here are some reasons to file a JIRA:

(0) Flaky tests are not always broken tests -- sometimes the underlying code is broken. (e.g.,
SPARK-19803<https://issues.apache.org/jira/browse/SPARK-19803>, SPARK-19988<https://issues.apache.org/jira/browse/SPARK-19988>,
SPARK-19072 <https://issues.apache.org/jira/browse/SPARK-19072> )

(1) Before a flaky test gets fixed, some human needs to file a JIRA.  The person who sees
the flaky test via the PR builder is best suited to do this, because you already had to look
at which test failed (to make sure it wasn't related to your change) and you know the test
is flaky (because you're re-running it assuming it will succeed), at which point it takes
<1 minute to file a JIRA

(2) Related to the above, existing automation is not sufficient.  Josh's tool is very useful
for debugging flaky tests [1] but it does not yet automatically file JIRAs.  Many recent flaky
tests might have shown up on the nifty interesting recent failures dashboard, but they didn't
get noticed until they were failing for more than a week and dropped from that dashboard.
 One recent test, SPARK-19990<https://issues.apache.org/jira/browse/SPARK-19990>, was
causing *every* Maven build to fail for over > 1 week, but was only noticed when someone
filed a JIRA as a result of a flaky PR test.

(3) JIRAs result in helpful people fixing the tests!  If you're interested in doing this,
the flaky test label<https://issues.apache.org/jira/browse/SPARK-19989?jql=project%20%3D%20SPARK%20AND%20status%20in%20(Open%2C%20Reopened)%20AND%20labels%20%3D%20flaky-test>
is a good place to start.  Many thanks to folks who have recently helped with filing and fixing
flaky tests: Sital Kedia, Song Jun, Xiao Li, Shubham Chopra, Shixiong Zhu, Genmao Yu, Imran
Rashid, and I'm sure many more (this list is based on a quick JIRA skim).

Thanks!!

Kay



[1] You can create a URL using the "suite_name" and optionally "test_name" GET parameters
in Josh's app to investigate a flaky test; e.g., to see how often the "hive bucketing is not
supported" test in ShowCreateTableSuite has been failing: https://spark-tests.appspot.com/test-details?suite_name=org.apache.spark.sql.hive.ShowCreateTableSuite&test_name=hive+bucketing+is+not+supported
(be patient -- it takes a minute and sometimes a re-load to work).


On Thu, Feb 16, 2017 at 9:22 AM, Reynold Xin <rxin@databricks.com<mailto:rxin@databricks.com>>
wrote:
Josh's tool should give enough signal there already. I don't think we need some manual process
to document them. If you want to work on those that'd be great. I bet you will get a lot of
love because all developers hate flaky tests.


On Thu, Feb 16, 2017 at 6:19 PM, Saikat Kanjilal <sxk1969@hotmail.com<mailto:sxk1969@hotmail.com>>
wrote:

I am specifically suggesting documenting a list of the the flaky tests and fixing them, that's
all.  To organize the effort I suggested tackling this by module.  Your second sentence is
what I was trying to gauge from the community before putting anymore effort into this.


________________________________
From: Sean Owen <sowen@cloudera.com<mailto:sowen@cloudera.com>>
Sent: Thursday, February 16, 2017 8:45 AM
To: Saikat Kanjilal; dev@spark.apache.org<mailto:dev@spark.apache.org>

Subject: Re: File JIRAs for all flaky test failures

I'm not sure what you're specifically suggesting. Of course flaky tests are bad and they should
be fixed, and people do. Yes, some are pretty hard to fix because they are rarely reproducible
if at all. If you want to fix, fix; there's nothing more to it.

I don't perceive flaky tests to be a significant problem. It has gone from bad to occasional
over the past year in my anecdotal experience.

On Thu, Feb 16, 2017 at 4:26 PM Saikat Kanjilal <sxk1969@hotmail.com<mailto:sxk1969@hotmail.com>>
wrote:

I'd just like to follow up again on this thread, should we devote some energy to fixing unit
tests based on module, there wasn't much interest in this last time but given the nature of
this thread I'd be willing to deep dive into this again with some help.

________________________________
From: Saikat Kanjilal <sxk1969@hotmail.com<mailto:sxk1969@hotmail.com>>
Sent: Wednesday, February 15, 2017 6:12 PM
To: Josh Rosen
Cc: Armin Braun; Kay Ousterhout; dev@spark.apache.org<mailto:dev@spark.apache.org>

Subject: Re: File JIRAs for all flaky test failures
The issue was not with a lack of tooling, I used the url you are describing below to drill
down to the exact test failure/stack trace, the problem was that my builds would work like
a charm locally but fail with these errors on Jenkins, this was the whole challenge in fixing
the unit tests, it was rare (if ever) where I would be able to replicate test failures locally.

Sent from my iPhone

On Feb 15, 2017, at 5:40 PM, Josh Rosen <joshrosen@databricks.com<mailto:joshrosen@databricks.com>>
wrote:

A useful tool for investigating test flakiness is my Jenkins Test Explorer service, running
at https://spark-tests.appspot.com/

This has some useful timeline views for debugging flaky builds. For instance, at https://spark-tests.appspot.com/jobs/spark-master-test-maven-hadoop-2.6
(may be slow to load) you can see this chart: https://i.imgur.com/j8LV3pX.png. Here, each
column represents a test run and each row represents a test which failed at least once over
the displayed time period.

In that linked example screenshot you'll notice that a few columns have grey squares indicating
that tests were skipped but lack any red squares to indicate test failures. This usually indicates
that the build failed due to a problem other than an individual test failure. For example,
I clicked into one of those builds and found that one test suite failed in test setup because
the previous suite had not properly cleaned up its SparkContext (I'll file a JIRA for this).

You can click through the interface to drill down to reports on individual builds, tests,
suites, etc. As an example of an individual test's detail page, https://spark-tests.appspot.com/test-details?suite_name=org.apache.spark.rdd.LocalCheckpointSuite&test_name=missing+checkpoint+block+fails+with+informative+message
shows the patterns of flakiness in a streaming checkpoint test.

Finally, there's an experimental "interesting new test failures" report which tries to surface
tests which have started failing very recently: https://spark-tests.appspot.com/failed-tests/new.
Specifically, entries in this feed are test failures which a) occurred in the last week, b)
were not part of a build which had 20 or more failed tests, and c) were not observed to fail
in during the previous week (i.e. no failures from [2 weeks ago, 1 week ago)), and d) which
represent the first time that the test failed this week (i.e. a test case will appear at most
once in the results list). I've also exposed this as an RSS feed at https://spark-tests.appspot.com/rss/failed-tests/new.


On Wed, Feb 15, 2017 at 12:51 PM Saikat Kanjilal <sxk1969@hotmail.com<mailto:sxk1969@hotmail.com>>
wrote:

I would recommend we just open JIRA's for unit tests based on module (core/ml/sql etc) and
we fix this one module at a time, this at least keeps the number of unit tests needing fixing
down to a manageable number.


________________________________
From: Armin Braun <me@obrown.io<mailto:me@obrown.io>>
Sent: Wednesday, February 15, 2017 12:48 PM
To: Saikat Kanjilal
Cc: Kay Ousterhout; dev@spark.apache.org<mailto:dev@spark.apache.org>
Subject: Re: File JIRAs for all flaky test failures

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<mailto: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.

[SPARK-9487] Use the same num. worker threads in Scala ...<https://issues.apache.org/jira/browse/SPARK-9487>
issues.apache.org<http://issues.apache.org>
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<mailto:kayousterhout@gmail.com>>
Sent: Wednesday, February 15, 2017 12:10 PM
To: dev@spark.apache.org<mailto: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!

-Kay




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