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https://issues.apache.org/jira/browse/HIVE-18825?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16382548#comment-16382548
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Eugene Koifman commented on HIVE-18825:
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this assumption is not valid. For one thing if you open the txn after you get
the list, you won't be able to read your writes, .i.e. your own txn will be
above the HWM that is set for you txn. The txn is currently opened right after
parsing - do you need ValidTxnList earlier than that?
> 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.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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