[SPARK-23381][CORE] Murmur3 hash generates a different value from other implementations by mrkm4ntr · Pull Request #20568 · apache/spark

mrkm4ntr · 2018-02-10T14:33:41Z

What changes were proposed in this pull request?

Murmur3 hash generates a different value from the original and other implementations (like Scala standard library and Guava or so) when the length of a bytes array is not multiple of 4.

How was this patch tested?

Added a unit test.

Please review http://spark.apache.org/contributing.html before opening a pull request.

kiszk · 2018-02-11T04:09:50Z

It would be good to add JIRA number with a short description as a comment (e.g. SPARK-23381 ...)

kiszk · 2018-02-11T04:10:27Z

Is it better to compare with the result of murmur3 hash value by scala library?

mrkm4ntr · 2018-02-11T09:51:53Z

@kiszk Thank you for your review! I fixed it.

hvanhovell · 2018-02-12T17:29:33Z

@mrkm4ntr The change itself looks pretty reasonable. However I am very hesitant to merge this because this will probably break bucketing (it uses murmur3 to create the buckets); for example a bucketed table written by Spark 2.2 cannot be safely read by Spark after this change.

Can you explain what problem you are trying to fix here?

mrkm4ntr · 2018-02-13T01:25:11Z

@hvanhovell The main motivation is making the online prediction of trained parameters using FeatureHasher in MLLib. If the generated hash value is different from the implementations in another language, indices of coefficients do not match and can not predict correctly.
But I agree backward compatibility is more important. Since FeatureHasher will be added from Spark 2.3.0, how about adding a new method of this content to Murmur 3 and using it only from FeatureHasher?

jiangxb1987 · 2018-02-14T08:30:54Z

How about add a new config to control whether to use the new Murmur3 hash function and have that default turned off? We also have to document the change explicitly. WDYT @gatorsmile @hvanhovell @cloud-fan ?

hvanhovell · 2018-02-14T12:54:50Z

@mrkm4ntr I see your point. Adding a method to Murmur3 would work.

The problem is that we are now going to release a FeatureHasher in Spark 2.3 that uses the current Murmur3 implementation. If we change this to use the correct Murmur3 implementation after the release of Spark 2.3 we will break all models using feature hashing created using Spark 2.3. This might be a blocker. Can you send an e-mail to the dev list?

cc @sameeragarwal @srowen for more visibility.

mrkm4ntr · 2018-02-14T14:08:41Z

@hvanhovell I sent an e-mail to the topic [VOTE] Spark 2.3.0 (RC3).

mrkm4ntr · 2018-02-15T05:48:45Z

@hvanhovell I added a method and changed it so that we call it only from FeatureHasher.

felixcheung · 2018-02-15T06:33:09Z

Jenkins, test this please

SparkQA · 2018-02-15T08:05:02Z

Test build #87472 has finished for PR 20568 at commit 336bce0.

This patch fails due to an unknown error code, -9.
This patch merges cleanly.
This patch adds no public classes.

cloud-fan · 2018-02-15T09:15:00Z

nit: Use this method for new components after Spark 2.3

Thanks, fixed it.

kiszk · 2018-02-15T14:33:11Z

Retest this please

…not a multiple of 4

mrkm4ntr · 2018-02-16T01:47:22Z

I cannot reproduce this failure of the test in my environment.
It seems to me that this is not related to this change...

kiszk · 2018-02-16T02:03:26Z

@mrkm4ntr Do not worry about these failures. Since we know there are some unstable tests, our community is trying to fix them. For a while, we have to kick test.

kiszk · 2018-02-16T02:03:38Z

Retest this please

ueshin · 2018-02-16T03:26:39Z

Jenkins, retest this please.

SparkQA · 2018-02-16T06:31:45Z

Test build #87501 has finished for PR 20568 at commit c20cd97.

This patch fails Spark unit tests.
This patch merges cleanly.
This patch adds no public classes.

kiszk · 2018-02-16T06:38:12Z

Jenkins, retest this please.

viirya · 2018-02-16T08:38:53Z

retest this please.

viirya · 2018-02-16T08:42:08Z

+ * See SPARK-23381.
+ */
+ @Since("2.3.0")
+ def murmur3Hash(term: Any): Int = {


Maybe private[feature]?

I would also address this comment.

felixcheung · 2018-02-16T09:41:30Z

Jenkins, retest this please.

SparkQA · 2018-02-16T12:58:20Z

Test build #87509 has finished for PR 20568 at commit c20cd97.

This patch fails PySpark unit tests.
This patch merges cleanly.
This patch adds no public classes.

kiszk · 2018-02-16T13:37:58Z

Jenkins, retest this please.

hvanhovell · 2018-02-16T17:48:10Z

@mrkm4ntr this is legitimate failure. Can you fix the python tests?

sameeragarwal · 2018-02-16T19:04:59Z

@hvanhovell just to make sure, given the dependency on FeatureHasher, should this block RC4?

jkbradley · 2018-02-16T20:24:21Z

(updated)

For ML, I actually don't think this has to be a blocker. It's not great, but it's not a regression.

However, we should definitely fix this in the future and soon: For ML, it's really important that MurmurHash3 behave consistently across platforms.

To fix this, we'll need to maintain the old implementation of MurmushHash3 to maintain the behavior of ML Pipelines exported from previous versions of Spark.

gatorsmile · 2018-02-16T20:53:50Z

To speedup the work here, I will take this over. All the contributions should be given to @mrkm4ntr

Thanks for your work! @mrkm4ntr

gatorsmile · 2018-02-16T21:25:08Z

Submitted the PR #20630 to take this over.

viirya · 2018-02-17T02:53:02Z

I think we can close this now.

gatorsmile · 2018-02-17T04:36:31Z

@mrkm4ntr Thank you for your contribution! The PR has been merged using your Github account. Could you close this?

mrkm4ntr · 2018-02-17T05:12:13Z

@gatorsmile Thanks! I will close it.

kiszk reviewed Feb 11, 2018
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mrkm4ntr force-pushed the spark-23381 branch from 8856e39 to 905ae19Compare February 11, 2018 09:47

mrkm4ntr force-pushed the spark-23381 branch from 905ae19 to 336bce0Compare February 15, 2018 05:41

cloud-fan reviewed Feb 15, 2018
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[SPARK-23381][CORE] Fix Murmur3 for byte arrays whose byte length is …
c20cd97
…not a multiple of 4

mrkm4ntr force-pushed the spark-23381 branch from 336bce0 to c20cd97Compare February 16, 2018 01:39

viirya reviewed Feb 16, 2018
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mrkm4ntr closed this Feb 17, 2018

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mrkm4ntr commented Feb 10, 2018

What changes were proposed in this pull request?

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