[jira] [Created] (IOTDB-1997) Fix incorrect AggregationResult generation in cluster DESC query

["Eric Pai (Jira)" <ji...@apache.org>]

Eric Pai created IOTDB-1997:
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             Summary: Fix incorrect AggregationResult generation in cluster DESC query
                 Key: IOTDB-1997
                 URL: https://issues.apache.org/jira/browse/IOTDB-1997
             Project: Apache IoTDB
          Issue Type: Bug
            Reporter: Eric Pai
             Fix For: master branch, 0.12.3


This bug can reappear by replaying the test case IoTDBAggregationIT.firstTest in a 3 nodes with 2 replicas cluster.

The main reason:

Consider this query in the above IT

 
{code:java}
"SELECT first_value(s0),first_value(s1),first_value(s2),first_value(s3) "
    + "FROM root.vehicle.d0 WHERE time >= 1500 AND time <= 9000 order by time desc" {code}
And see the codes in [https://github.com/apache/iotdb/blob/e08525072a88e6a99ee2026352fb133f40e7c3ee/cluster/src/main/java/org/apache/iotdb/cluster/query/LocalQueryExecutor.java#L693-L738]

 

If we query by DESC, the ascending == false, and we get the AggregationResult is FirstValueDescAggrResult, which should read data in decending order and calculate result.

Howerver, in the AggregationExecutor.aggregateOneSeries, the reader generated is also a decending one, it will return a descending read BatchData when calling AggregationResult.updateResultFromPageData(). 

Now let's investigate the implementation of FirstValueDescAggrResult.updateResultFromPageData(BatchData). It 'treats' the input BatchData as an ascending read sequence one(it will return the first data without any loop), which is a contradiction with the reader generated, thus the bug occurs.

Here is a brief explain:

The page data in order: 1,2,3

The generated decending reader page data with the read sequence: 3,2,1

And the FirstValueDescAggrResult will return the first one data, '3', which is different from our expected '1'

So I think the best solution is to put the AggregationResult in an ascResultList and descResultList according to the method AggregationResult.isAscending().

And we should add a comment to isAscending() interface.

 



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