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https://issues.apache.org/jira/browse/HIVE-26150?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17527968#comment-17527968
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Peter Vary commented on HIVE-26150:
-----------------------------------
[~asolimando]: I am trying to find out if fixing this issue would cause
performance improvements when reading tables where we have delete deltas
present.
We have two ways to read the delete deltas:
- [SortMergedDeleteEventRegistry
|https://github.com/apache/hive/blob/a29810ce97a726fc70aecb53ebd648c3237106c4/ql/src/java/org/apache/hadoop/hive/ql/io/orc/VectorizedOrcAcidRowBatchReader.java#L1228]
- [ColumnizedDeleteEventRegistry
|https://github.com/apache/hive/blob/a29810ce97a726fc70aecb53ebd648c3237106c4/ql/src/java/org/apache/hadoop/hive/ql/io/orc/VectorizedOrcAcidRowBatchReader.java#L1383]
IIRC the ColumnizedDeleteEventRegistry creates its own readers and
SortMergedDeleteEventRegistry uses OrcRawRecordMerger, so I would guess that
the normal reads would be effected with this inefficiency when
SortMergedDeleteEventRegistry is used, but I would like this to be confirmed.
Thanks,
Peter
> OrcRawRecordMerger reads each row twice
> ---------------------------------------
>
> Key: HIVE-26150
> URL: https://issues.apache.org/jira/browse/HIVE-26150
> Project: Hive
> Issue Type: Bug
> Components: ORC, Transactions
> Affects Versions: 4.0.0-alpha-2
> Reporter: Alessandro Solimando
> Priority: Major
>
> OrcRawRecordMerger reads each row twice, the issue does not surface since the
> merger is only used with the parameter "collapseEvents" as true, which
> filters out one of the two rows.
> collapseEvents true and false should produce the same result, since in
> current acid implementation, each event has a distinct rowid, so two
> identical rows cannot be there, this is the case only for the bug.
> In order to reproduce the issue, it is sufficient to set the second parameter
> to false
> [here|https://github.com/apache/hive/blob/61d4ff2be48b20df9fd24692c372ee9c2606babe/ql/src/java/org/apache/hadoop/hive/ql/io/orc/OrcInputFormat.java#L2103-L2106],
> and run tests in TestOrcRawRecordMerger and observe two tests failing:
> {code:bash}
> mvn test -Dtest=TestOrcRawRecordMerger -pl ql
> {code}
> {noformat}
> [INFO] Results:
> [INFO]
> [ERROR] Failures:
> [ERROR] TestOrcRawRecordMerger.testRecordReaderNewBaseAndDelta:1332 Found
> unexpected row: (0,ignore.1)
> [ERROR] TestOrcRawRecordMerger.testRecordReaderOldBaseAndDelta:1208 Found
> unexpected row: (0,ignore.1)
> {noformat}
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