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https://issues.apache.org/jira/browse/MAHOUT-1810?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15200163#comment-15200163
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Andrew Palumbo edited comment on MAHOUT-1810 at 3/18/16 4:21 PM:
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-From the above tests though we can see that in the case of {{B %*% A.t}} where
{{B}} is a checkpointed non-deterministic matrix, Checkpointing is creating a
barrier. I should have illustrated this better by Using A+B and also providing
failure case. (I was also using it as a sanity test for FlinkOpAtB) But it
does in fact fail without the checkpoint of {{B}}-.
*Edit Note*: Same as above.
It seems that checkpointing the mapBlock result is the culprit. Maybe this
speaks to your point about intermediate caching.
was (Author: andrew_palumbo):
>From the above tests though we can see that in the case of {{B %*% A.t}} where
>{{B}} is a checkpointed non-deterministic matrix, Checkpointing is creating a
>barrier. I should have illustrated this better by Using A+B and also
>providing failure case. (I was also using it as a sanity test for FlinkOpAtB)
>But it does in fact fail without the checkpoint of {{B}}.
It seems that checkpointing the mapBlock result is the culprit. Maybe this
speaks to your point about intermediate caching.
> Failing test in flink-bindings: A + B Identically partitioned
> -------------------------------------------------------------
>
> Key: MAHOUT-1810
> URL: https://issues.apache.org/jira/browse/MAHOUT-1810
> Project: Mahout
> Issue Type: Bug
> Reporter: Andrew Palumbo
> Assignee: Andrew Palumbo
> Priority: Blocker
> Fix For: 0.12.0
>
>
> the {{A + B, Identically Partitioned}} test in the Flink RLikeDrmOpsSuite
> fails. This test failure likely indicates an issue with Flink's
> Checkpointing or mapBlock operator:
> {code}
> test("C = A + B, identically partitioned") {
> val inCoreA = dense((1, 2, 3), (3, 4, 5), (5, 6, 7))
> val A = drmParallelize(inCoreA, numPartitions = 2)
> // Create B which would be identically partitioned to A. mapBlock() by
> default will do the trick.
> val B = A.mapBlock() {
> case (keys, block) =>
> val bBlock = block.like() := { (r, c, v) => util.Random.nextDouble()}
> keys -> bBlock
> }
> // Prevent repeated computation non-determinism
> // flink problem is here... checkpoint is not doing what it should
> .checkpoint()
> val inCoreB = B.collect
> printf("A=\n%s\n", inCoreA)
> printf("B=\n%s\n", inCoreB)
> val C = A + B
> val inCoreC = C.collect
> printf("C=\n%s\n", inCoreC)
> // Actual
> val inCoreCControl = inCoreA + inCoreB
> (inCoreC - inCoreCControl).norm should be < 1E-10
> }
> {code}
> The output shous clearly that the line:
> {code}
> val bBlock = block.like() := { (r, c, v) => util.Random.nextDouble()}
> {code}
> in the {{mapBlock}} closure is being calculated more than once.
> Output:
> {code}
> A=
> {
> 0 => {0:1.0,1:2.0,2:3.0}
> 1 => {0:3.0,1:4.0,2:5.0}
> 2 => {0:5.0,1:6.0,2:7.0}
> }
> B=
> {
> 0 => {0:0.26203398262809574,1:0.22561543461472167,2:0.23229669514522655}
> 1 => {0:0.1638068194515867,1:0.18751822418846575,2:0.20586366231381614}
> 2 => {0:0.9279465706239354,1:0.2963513448240057,2:0.8866928923235948}
> }
> C=
> {
> 0 => {0:1.7883652623225594,1:2.6401297718606216,2:3.0023341959374195}
> 1 => {0:3.641411452208408,1:4.941233165480053,2:5.381282338548803}
> 2 => {0:5.707434148862531,1:6.022780876943659,2:7.149772825494352}
> }
> {code}
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