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https://issues.apache.org/jira/browse/HIVE-20901?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16810472#comment-16810472
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Abhishek Somani commented on HIVE-20901:
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Right. The patch I have uploaded will avoid the duplicate compaction in the
first place.
I also think it is worth fixing this in the 3.1 branch where we do not have
visibility ids.
> running compactor when there is nothing to do produces duplicate data
> ---------------------------------------------------------------------
>
> Key: HIVE-20901
> URL: https://issues.apache.org/jira/browse/HIVE-20901
> Project: Hive
> Issue Type: Bug
> Components: Transactions
> Affects Versions: 4.0.0
> Reporter: Eugene Koifman
> Assignee: Abhishek Somani
> Priority: Major
> Attachments: HIVE-20901.1.patch
>
>
> suppose we run minor compaction 2 times, via alter table
> The 2nd request to compaction should have nothing to do but I don't think
> there is a check for that. It's visible in the context of HIVE-20823, where
> each compactor run produces a delta with new visibility suffix so we end up
> with something like
> {noformat}
> target/tmp/org.apache.hadoop.hive.ql.TestTxnCommands3-1541810844849/warehouse/t/
> ├── delete_delta_0000001_0000002_v0000019
> │ ├── _orc_acid_version
> │ └── bucket_00000
> ├── delete_delta_0000001_0000002_v0000021
> │ ├── _orc_acid_version
> │ └── bucket_00000
> ├── delta_0000001_0000001_0000
> │ ├── _orc_acid_version
> │ └── bucket_00000
> ├── delta_0000001_0000002_v0000019
> │ ├── _orc_acid_version
> │ └── bucket_00000
> ├── delta_0000001_0000002_v0000021
> │ ├── _orc_acid_version
> │ └── bucket_00000
> └── delta_0000002_0000002_0000
> ├── _orc_acid_version
> └── bucket_00000{noformat}
> i.e. 2 deltas with the same write ID range
> this is bad. Probably happens today as well but new run produces a delta
> with the same name and clobbers the previous one, which may interfere with
> writers
>
> need to investigate
>
> -The issue (I think) is that {{AcidUtils.getAcidState()}} then returns both
> deltas as if they were distinct and it effectively duplicates data.- There
> is no data duplication - {{getAcidState()}} will not use 2 deltas with the
> same {{writeid}} range
>
>
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