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https://issues.apache.org/jira/browse/HIVE-16669?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16405648#comment-16405648
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Eugene Koifman commented on HIVE-16669:
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if compactor runs in a txn, it must write to min_history. Suppose txnid:7 is
A, txnid:70 is Compactor. 71 starts and sees 7 as A and 70 as O. If 70 makes
7 empty we need to make sure {{cleanEmptyAbortedTxns()}} doesn't remove 7's
entry from TXNS since files produced by 70 are not visible to 71 and if 70
reads older files, it will treat 7's data as committed (if
{{cleanEmptyAbortedTxns()}} runs).
> Fine tune Compaction to take advantage of Acid 2.0
> --------------------------------------------------
>
> Key: HIVE-16669
> URL: https://issues.apache.org/jira/browse/HIVE-16669
> Project: Hive
> Issue Type: Bug
> Components: Transactions
> Reporter: Eugene Koifman
> Assignee: Eugene Koifman
> Priority: Critical
> Attachments: HIVE-16669.wip.patch
>
>
> * There is little point using 2.0 vectorized reader since there is no
> operator pipeline in compaction
> * If minor compaction just concats delete_delta files together, then the 2
> stage compaction should always ensure that we have a limited number of Orc
> readers to do the merging and current OrcRawRecordMerger should be fine
> * ...
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