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Posted to reviews@spark.apache.org by tdas <gi...@git.apache.org> on 2018/03/08 02:02:59 UTC
[GitHub] spark pull request #20765: [SPARK-23406][SS] Enable stream-stream self-joins...
GitHub user tdas opened a pull request:
https://github.com/apache/spark/pull/20765
[SPARK-23406][SS] Enable stream-stream self-joins for branch-2.3
This is a backport of #20598.
## What changes were proposed in this pull request?
Solved two bugs to enable stream-stream self joins.
### Incorrect analysis due to missing MultiInstanceRelation trait
Streaming leaf nodes did not extend MultiInstanceRelation, which is necessary for the catalyst analyzer to convert the self-join logical plan DAG into a tree (by creating new instances of the leaf relations). This was causing the error `Failure when resolving conflicting references in Join:` (see JIRA for details).
### Incorrect attribute rewrite when splicing batch plans in MicroBatchExecution
When splicing the source's batch plan into the streaming plan (by replacing the StreamingExecutionPlan), we were rewriting the attribute reference in the streaming plan with the new attribute references from the batch plan. This was incorrectly handling the scenario when multiple StreamingExecutionRelation point to the same source, and therefore eventually point to the same batch plan returned by the source. Here is an example query, and its corresponding plan transformations.
```
val df = input.toDF
val join =
df.select('value % 5 as "key", 'value).join(
df.select('value % 5 as "key", 'value), "key")
```
Streaming logical plan before splicing the batch plan
```
Project [key#6, value#1, value#12]
+- Join Inner, (key#6 = key#9)
:- Project [(value#1 % 5) AS key#6, value#1]
: +- StreamingExecutionRelation Memory[#1], value#1
+- Project [(value#12 % 5) AS key#9, value#12]
+- StreamingExecutionRelation Memory[#1], value#12 // two different leaves pointing to same source
```
Batch logical plan after splicing the batch plan and before rewriting
```
Project [key#6, value#1, value#12]
+- Join Inner, (key#6 = key#9)
:- Project [(value#1 % 5) AS key#6, value#1]
: +- LocalRelation [value#66] // replaces StreamingExecutionRelation Memory[#1], value#1
+- Project [(value#12 % 5) AS key#9, value#12]
+- LocalRelation [value#66] // replaces StreamingExecutionRelation Memory[#1], value#12
```
Batch logical plan after rewriting the attributes. Specifically, for spliced, the new output attributes (value#66) replace the earlier output attributes (value#12, and value#1, one for each StreamingExecutionRelation).
```
Project [key#6, value#66, value#66] // both value#1 and value#12 replaces by value#66
+- Join Inner, (key#6 = key#9)
:- Project [(value#66 % 5) AS key#6, value#66]
: +- LocalRelation [value#66]
+- Project [(value#66 % 5) AS key#9, value#66]
+- LocalRelation [value#66]
```
This causes the optimizer to eliminate value#66 from one side of the join.
```
Project [key#6, value#66, value#66]
+- Join Inner, (key#6 = key#9)
:- Project [(value#66 % 5) AS key#6, value#66]
: +- LocalRelation [value#66]
+- Project [(value#66 % 5) AS key#9] // this does not generate value, incorrect join results
+- LocalRelation [value#66]
```
**Solution**: Instead of rewriting attributes, use a Project to introduce aliases between the output attribute references and the new reference generated by the spliced plans. The analyzer and optimizer will take care of the rest.
```
Project [key#6, value#1, value#12]
+- Join Inner, (key#6 = key#9)
:- Project [(value#1 % 5) AS key#6, value#1]
: +- Project [value#66 AS value#1] // solution: project with aliases
: +- LocalRelation [value#66]
+- Project [(value#12 % 5) AS key#9, value#12]
+- Project [value#66 AS value#12] // solution: project with aliases
+- LocalRelation [value#66]
```
## How was this patch tested?
New unit test
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/tdas/spark SPARK-23406-2.3
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/20765.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #20765
----
commit c3ec9ef9355a3290d764dda0191165eaa4e49062
Author: Tathagata Das <ta...@...>
Date: 2018-02-14T22:27:02Z
[SPARK-23406][SS] Enable stream-stream self-joins
## What changes were proposed in this pull request?
Solved two bugs to enable stream-stream self joins.
### Incorrect analysis due to missing MultiInstanceRelation trait
Streaming leaf nodes did not extend MultiInstanceRelation, which is necessary for the catalyst analyzer to convert the self-join logical plan DAG into a tree (by creating new instances of the leaf relations). This was causing the error `Failure when resolving conflicting references in Join:` (see JIRA for details).
### Incorrect attribute rewrite when splicing batch plans in MicroBatchExecution
When splicing the source's batch plan into the streaming plan (by replacing the StreamingExecutionPlan), we were rewriting the attribute reference in the streaming plan with the new attribute references from the batch plan. This was incorrectly handling the scenario when multiple StreamingExecutionRelation point to the same source, and therefore eventually point to the same batch plan returned by the source. Here is an example query, and its corresponding plan transformations.
```
val df = input.toDF
val join =
df.select('value % 5 as "key", 'value).join(
df.select('value % 5 as "key", 'value), "key")
```
Streaming logical plan before splicing the batch plan
```
Project [key#6, value#1, value#12]
+- Join Inner, (key#6 = key#9)
:- Project [(value#1 % 5) AS key#6, value#1]
: +- StreamingExecutionRelation Memory[#1], value#1
+- Project [(value#12 % 5) AS key#9, value#12]
+- StreamingExecutionRelation Memory[#1], value#12 // two different leaves pointing to same source
```
Batch logical plan after splicing the batch plan and before rewriting
```
Project [key#6, value#1, value#12]
+- Join Inner, (key#6 = key#9)
:- Project [(value#1 % 5) AS key#6, value#1]
: +- LocalRelation [value#66] // replaces StreamingExecutionRelation Memory[#1], value#1
+- Project [(value#12 % 5) AS key#9, value#12]
+- LocalRelation [value#66] // replaces StreamingExecutionRelation Memory[#1], value#12
```
Batch logical plan after rewriting the attributes. Specifically, for spliced, the new output attributes (value#66) replace the earlier output attributes (value#12, and value#1, one for each StreamingExecutionRelation).
```
Project [key#6, value#66, value#66] // both value#1 and value#12 replaces by value#66
+- Join Inner, (key#6 = key#9)
:- Project [(value#66 % 5) AS key#6, value#66]
: +- LocalRelation [value#66]
+- Project [(value#66 % 5) AS key#9, value#66]
+- LocalRelation [value#66]
```
This causes the optimizer to eliminate value#66 from one side of the join.
```
Project [key#6, value#66, value#66]
+- Join Inner, (key#6 = key#9)
:- Project [(value#66 % 5) AS key#6, value#66]
: +- LocalRelation [value#66]
+- Project [(value#66 % 5) AS key#9] // this does not generate value, incorrect join results
+- LocalRelation [value#66]
```
**Solution**: Instead of rewriting attributes, use a Project to introduce aliases between the output attribute references and the new reference generated by the spliced plans. The analyzer and optimizer will take care of the rest.
```
Project [key#6, value#1, value#12]
+- Join Inner, (key#6 = key#9)
:- Project [(value#1 % 5) AS key#6, value#1]
: +- Project [value#66 AS value#1] // solution: project with aliases
: +- LocalRelation [value#66]
+- Project [(value#12 % 5) AS key#9, value#12]
+- Project [value#66 AS value#12] // solution: project with aliases
+- LocalRelation [value#66]
```
## How was this patch tested?
New unit test
Author: Tathagata Das <ta...@gmail.com>
Closes #20598 from tdas/SPARK-23406.
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[GitHub] spark issue #20765: [SPARK-23406][SS] Enable stream-stream self-joins for br...
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[GitHub] spark issue #20765: [SPARK-23406][SS] Enable stream-stream self-joins for br...
Posted by SparkQA <gi...@git.apache.org>.
Github user SparkQA commented on the issue:
https://github.com/apache/spark/pull/20765
**[Test build #88067 has finished](https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder/88067/testReport)** for PR 20765 at commit [`c3ec9ef`](https://github.com/apache/spark/commit/c3ec9ef9355a3290d764dda0191165eaa4e49062).
* This patch passes all tests.
* This patch merges cleanly.
* This patch adds no public classes.
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[GitHub] spark issue #20765: [SPARK-23406][SS] Enable stream-stream self-joins for br...
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[GitHub] spark issue #20765: [SPARK-23406][SS] Enable stream-stream self-joins for br...
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Github user SparkQA commented on the issue:
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**[Test build #88067 has started](https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder/88067/testReport)** for PR 20765 at commit [`c3ec9ef`](https://github.com/apache/spark/commit/c3ec9ef9355a3290d764dda0191165eaa4e49062).
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[GitHub] spark pull request #20765: [SPARK-23406][SS] Enable stream-stream self-joins...
Posted by tdas <gi...@git.apache.org>.
Github user tdas closed the pull request at:
https://github.com/apache/spark/pull/20765
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[GitHub] spark issue #20765: [SPARK-23406][SS] Enable stream-stream self-joins for br...
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