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https://issues.apache.org/jira/browse/HIVE-19985?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16565600#comment-16565600
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Eugene Koifman commented on HIVE-19985:
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The logic whether to pass ROW_ID up or not is not changed by this patch.
Previously, we decoded the values from storage unconditionally and then the
acid reader simply dropped them. Now it takes it one step further and doesn't
decode them if they are not needed. In short, this should have no functional
impact above the reader.
> ACID: Skip decoding the ROW__ID sections for read-only queries
> ---------------------------------------------------------------
>
> Key: HIVE-19985
> URL: https://issues.apache.org/jira/browse/HIVE-19985
> Project: Hive
> Issue Type: Improvement
> Components: Transactions
> Reporter: Gopal V
> Assignee: Eugene Koifman
> Priority: Major
> Labels: Branch3Candidate
> Attachments: HIVE-19985.01.patch
>
>
> For a base_n file there are no aborted transactions within the file and if
> there are no pending delete deltas, the entire ACID ROW__ID can be skipped
> for all read-only queries (i.e SELECT), though it still needs to be projected
> out for MERGE, UPDATE and DELETE queries.
> This patch tries to entirely ignore the ACID ROW__ID fields for all tables
> where there are no possible deletes or aborted transactions for an ACID split.
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