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Fix resultcache multiple postaggregation restore #15402

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merged 5 commits into from
Nov 21, 2023
Merged

Fix resultcache multiple postaggregation restore #15402

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660d156
Fix resultcache multiple postaggregation restore
kgyrtkirk Nov 20, 2023
f744dd0
updates
kgyrtkirk Nov 20, 2023
137e8b5
Revert "updates"
kgyrtkirk Nov 20, 2023
d63064b
add exception
kgyrtkirk Nov 20, 2023
b566997
use druidexception
kgyrtkirk Nov 21, 2023
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5 changes: 1 addition & 4 deletions processing/src/main/java/org/apache/druid/query/groupby/GroupByQueryQueryToolChest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -62,7 +62,6 @@
import org.apache.druid.query.aggregation.AggregatorFactory;
import org.apache.druid.query.aggregation.MetricManipulationFn;
import org.apache.druid.query.aggregation.MetricManipulatorFns;
import org.apache.druid.query.aggregation.PostAggregator;
import org.apache.druid.query.cache.CacheKeyBuilder;
import org.apache.druid.query.context.ResponseContext;
import org.apache.druid.query.dimension.DefaultDimensionSpec;
Expand Down Expand Up @@ -651,9 +650,7 @@ public ResultRow apply(Object input)
);

if (isResultLevelCache) {
Iterator<PostAggregator> postItr = query.getPostAggregatorSpecs().iterator();
int postPos = 0;
while (postItr.hasNext() && results.hasNext()) {
for (int postPos = 0; postPos < query.getPostAggregatorSpecs().size(); postPos++) {
resultRow.set(postAggregatorStart + postPos, results.next());
}
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I am not sure if this can happen but to be on the safe side?

Suggested change
for (int postPos = 0; postPos < query.getPostAggregatorSpecs().size(); postPos++) {
resultRow.set(postAggregatorStart + postPos, results.next());
}
for (int postPos = 0; postPos < query.getPostAggregatorSpecs().size(); postPos++) {
if (results.hasNext()) resultRow.set(postAggregatorStart + postPos, results.next());
}

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I think the contract around here should be to restore the same row that it have saved into the cache - if its not able to do so; I think it should fail with an exception - if it doesn't do that wouldn't that cause incorrect results - or not?

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@LakshSingla LakshSingla Nov 20, 2023 •
edited
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I was also going through this area for a different purpose, and indeed there's a check below this code that checks if both the iterators have been exhausted completely, so even with the above check, the code would fail below. However, the error message would be more descriptive, so I think we should add the check back, otherwise it would fail with a generic NoSuchElementException exception

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not sure about the case you were thinking - but I'm afraid that check might not be that usefull for these cases; consider the following:

  • lets have
    • a results with {1 dim}+{1 aggs}+{1 postagg} = 3
    • a resultRow with {1 dim}+{1 aggs}+{2 postagg} = 4 (for whatever reason ?)
    • since in these cases the system is already facing a serious error - I'm not sure what value a nicer error message will give - as such error could not be fixed easily for sure
  • I think a more reasonable check would be to ensure that results.size() == resultRow.size() - so that we can remove the checking of all these iterators - as they are trying to do the same in a more complicated way

I've added an if to throw an exception in case there are no next when there should be one; but all these conditionals are kinda redundant as the iterator was created for a list

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@LakshSingla LakshSingla Nov 21, 2023 •
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https://github.com/apache/druid/blob/master/processing/src/main/java/org/apache/druid/query/groupby/GroupByQueryQueryToolChest.java#L660
I was referring to this check. It should also handle the case that you mentioned above right? Perhaps adding the size check that you mentioned earlier is more legible. I am okay with the code either way.

}
Expand Down
9 changes: 5 additions & 4 deletions processing/src/test/java/org/apache/druid/query/groupby/GroupByQueryQueryToolChestTest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -986,7 +986,8 @@ private void doTestCacheStrategy(final ColumnType valueType, final Object dimVal
)
)
.setPostAggregatorSpecs(
ImmutableList.of(new ConstantPostAggregator("post", 10))
new ConstantPostAggregator("post", 10),
new ConstantPostAggregator("post2", 20)
)
.setGranularity(QueryRunnerTestHelper.DAY_GRAN)
.build();
Expand Down Expand Up @@ -1017,14 +1018,14 @@ private void doTestCacheStrategy(final ColumnType valueType, final Object dimVal
Assert.assertEquals(result1, fromCacheResult);

// test timestamps that result in integer size millis
final ResultRow result2 = ResultRow.of(123L, dimValue, 1, dimValue, 10);
final ResultRow result2 = ResultRow.of(123L, dimValue, 1, dimValue, 10, 20);

// Please see the comments on aggregator serde and type handling in CacheStrategy.fetchAggregatorsFromCache()
final ResultRow typeAdjustedResult2;
if (valueType.is(ValueType.FLOAT)) {
typeAdjustedResult2 = ResultRow.of(123L, dimValue, 1, 2.1d, 10);
typeAdjustedResult2 = ResultRow.of(123L, dimValue, 1, 2.1d, 10, 20);
} else if (valueType.is(ValueType.LONG)) {
typeAdjustedResult2 = ResultRow.of(123L, dimValue, 1, 2, 10);
typeAdjustedResult2 = ResultRow.of(123L, dimValue, 1, 2, 10, 20);
} else {
typeAdjustedResult2 = result2;
}
Expand Down