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https://issues.apache.org/jira/browse/BEAM-6427?focusedWorklogId=185146&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-185146
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ASF GitHub Bot logged work on BEAM-6427:
----------------------------------------
Author: ASF GitHub Bot
Created on: 15/Jan/19 06:25
Start Date: 15/Jan/19 06:25
Worklog Time Spent: 10m
Work Description: kennknowles commented on pull request #7504:
[BEAM-6427] INTERSECT ALL is not compatible with SQL standard.
URL: https://github.com/apache/beam/pull/7504#discussion_r247775196
##########
File path:
sdks/java/extensions/sql/src/main/java/org/apache/beam/sdk/extensions/sql/impl/transform/BeamSetOperatorsTransforms.java
##########
@@ -80,8 +80,23 @@ public void processElement(ProcessContext ctx) {
case INTERSECT:
if (leftRows.iterator().hasNext() && rightRows.iterator().hasNext())
{
if (all) {
- for (Row leftRow : leftRows) {
- ctx.output(leftRow);
+ Iterator<Row> iter = leftRows.iterator();
+ int leftCount = 0;
+ int rightCount = 0;
+ while (iter.hasNext()) {
+ iter.next();
+ leftCount++;
+ }
+ iter = rightRows.iterator();
+ while (iter.hasNext()) {
+ iter.next();
+ rightCount++;
+ }
+
+ // output MIN(m, n)
+ iter = (leftCount <= rightCount) ? leftRows.iterator() :
rightRows.iterator();
+ while (iter.hasNext()) {
Review comment:
I had the same thought. To do the `row -> KV<row, count>` without a shuffle
(and we definitely want to do some version of it before a shuffle) there are
lots of performance considerations and some nondeterminism. The Dataflow
implementation is now open source
[here](https://github.com/apache/beam/blob/master/runners/google-cloud-dataflow-java/worker/src/main/java/org/apache/beam/runners/dataflow/worker/PartialGroupByKeyParDoFns.java)
and we could do something like that in a `ParDo`. Data consistency requires
that this be followed up by a full combine. The intermediate results do not
work as any kind of `Rel` but we _can_ use this as intermediate PCollections
just for doing set operations. It would have to actually be:
`row -> KV<row, partial count> -> CoGBK -> KV<row, [partial counts],
[partials counts]>` but small iterables of the partial counts that are easy to
sum inline with the emit logic.
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Issue Time Tracking
-------------------
Worklog Id: (was: 185146)
Time Spent: 2h (was: 1h 50m)
> INTERSECT ALL is not compatible with SQL standard
> -------------------------------------------------
>
> Key: BEAM-6427
> URL: https://issues.apache.org/jira/browse/BEAM-6427
> Project: Beam
> Issue Type: Improvement
> Components: dsl-sql
> Reporter: Rui Wang
> Assignee: Rui Wang
> Priority: Major
> Time Spent: 2h
> Remaining Estimate: 0h
>
> say Row R appears m times on one side and n times on another side.
> Beam's INTERSECT ALL is implemented to return MAX(m, n).
> And SQL1999 standard says INTERSECT ALL should return MIN(m, n).
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