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https://issues.apache.org/jira/browse/BEAM-6427?focusedWorklogId=185385&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-185385
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ASF GitHub Bot logged work on BEAM-6427:
----------------------------------------
Author: ASF GitHub Bot
Created on: 15/Jan/19 18:54
Start Date: 15/Jan/19 18:54
Worklog Time Spent: 10m
Work Description: amaliujia commented on pull request #7504: [BEAM-6427]
INTERSECT ALL is not compatible with SQL standard.
URL: https://github.com/apache/beam/pull/7504#discussion_r248019302
##########
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:
If we cannot avoid shuffle, passing around value or counts will sometime not
really impact performance. It really depends. I remember one problem faced by
shuffle is too many small files. Because by the nature of shuffle, there will
might be m * n connections where m is the number of mappers, n is the number of
keys/small files on each mapper. Some optimization on shuffle that might be
done is compact files into larger files, or pipeline might enable external
shuffle service.
Basically I think one solution is not always be optimal all the time.
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Issue Time Tracking
-------------------
Worklog Id: (was: 185385)
Time Spent: 2h 20m (was: 2h 10m)
> 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
> Fix For: Not applicable
>
> Time Spent: 2h 20m
> 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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