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

["Jialin Qiao (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/IOTDB-1997?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17443008#comment-17443008 ] 

Jialin Qiao commented on IOTDB-1997:
------------------------------------

https://github.com/apache/iotdb/pull/4373

> 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
>            Assignee: Eric Pai
>            Priority: Major
>             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
> 1. Fix FirstValueDescAggrResult implementation.
> 2. put the AggregationResult in an ascResultList and descResultList according to the method AggregationResult.isAscending().
> And we should add a comment to the abstract class AggregationResult interface.
>  
> What's more, 
>  



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