HIVE-28549: Limit the maximum number of operators merged by SharedWorkOptimizer #5492
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okumin
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deniskuzZ
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Oct 23, 2024
| final List<TableScanOperator> scans = tableNameToOps.get(tableName); | ||
| if (batchSize == -1) { | ||
| batches.add(scans); | ||
| continue; |
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using continue keyword is a bad practice
ngsg
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Nov 7, 2024
ql/src/java/org/apache/hadoop/hive/ql/optimizer/SharedWorkOptimizer.java
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ngsg
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Nov 12, 2024
| ArrayListMultimap<String, TableScanOperator> tableNameToOps, int batchSize) { | ||
| if (batchSize == -1) { | ||
| return Collections.singletonList(sortedTables.stream().map(Entry::getKey) | ||
| .flatMap(tableName -> tableNameToOps.get(tableName).stream()).collect(Collectors.toList())); |
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This puts all TS ops into a single List, regardless of their source. Maybe you intend the following code?
if (batchSize == -1) {
return sortedTables.stream()
.map(entry -> tableNameToOps.get(entry.getKey()))
.collect(Collectors.toList());
}
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You're right. I was just confused when I wrote the line. I modified it and ran some qtests which failed
e574161
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What changes were proposed in this pull request?
This PR would limit the maximum number of table scan operators which SWO tries to merge.
https://issues.apache.org/jira/browse/HIVE-28549
Why are the changes needed?
We observed SWO makes a negative impact when it merges too many, e.g. 50, operators. If operators are memory intensive, they might throw OOM or might slow down.
I believe we can resolve OOM with the following patch, but we still want an upper limit so that we can tune concurrency or RAM per operator reasonably.
#5478
Does this PR introduce any user-facing change?
No.
Is the change a dependency upgrade?
No.
How was this patch tested?
I added a qtest