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https://issues.apache.org/jira/browse/HIVE-18825?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16391880#comment-16391880
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Eugene Koifman commented on HIVE-18825:
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The Lock manger is entirely based on Read/WriteEntities created by compiler.
If you move lock acquisition to some place before they are available, you
basically need to rewrite the entire logic in the LM that is used to figure out
what to lock. It may be possible but it's an unpredictably large amount of
work which makes pessimistic locking an impractically expensive feature.
Incremental refresh is not prevented by this, though I understand that there
are some possible performance optimizations that are difficult w/o this.
> Define ValidTxnList before starting query optimization
> ------------------------------------------------------
>
> Key: HIVE-18825
> URL: https://issues.apache.org/jira/browse/HIVE-18825
> Project: Hive
> Issue Type: Improvement
> Components: Transactions
> Affects Versions: 3.0.0
> Reporter: Jesus Camacho Rodriguez
> Assignee: Jesus Camacho Rodriguez
> Priority: Major
> Attachments: HIVE-18825.01.patch, HIVE-18825.02.patch,
> HIVE-18825.03.patch, HIVE-18825.04.patch, HIVE-18825.patch
>
>
> Consider a set of tables used by a materialized view where inserts happened
> after the materialization was created. To compute incremental view
> maintenance, we need to be able to filter only new rows from those base
> tables. That can be done by inserting a filter operator with condition e.g.
> {{ROW\_\_ID.transactionId < highwatermark and ROW\_\_ID.transactionId NOT
> IN(<open txns>)}} on top of the MVs query definition and triggering the
> rewriting (which should in turn produce a partial rewriting). However, to do
> that, we need to have a value for {{ValidTxnList}} during query compilation
> so we know the snapshot that we are querying.
> This patch aims to generate {{ValidTxnList}} before query optimization. There
> should not be any visible changes for end user.
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