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https://issues.apache.org/jira/browse/HIVE-18923?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Sankar Hariappan reassigned HIVE-18923:
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Assignee: Sushil Ks (was: Sankar Hariappan)
> ValidWriteIdList snapshot per table can be cached for multi-statement
> transactions.
> -----------------------------------------------------------------------------------
>
> Key: HIVE-18923
> URL: https://issues.apache.org/jira/browse/HIVE-18923
> Project: Hive
> Issue Type: Bug
> Components: Transactions
> Affects Versions: 3.0.0
> Reporter: Sankar Hariappan
> Assignee: Sushil Ks
> Priority: Minor
> Labels: ACID
> Fix For: 3.2.0
>
>
> Currently, for each query within a multi-statement transaction, it would
> request metastore/TxnHandler to build ValidWriteIdList snapshot for the given
> table. This is costly as it need to talk to metastore RDBMS. But, the
> snapshot won't change within the duration of transaction. So, it make sense
> to cache it within QueryTxnManager for better performance.
> However, each txn should be able to view their own written rows. So, when a
> transaction allocates writeId to write on a table, then the cached
> ValidWriteIdList on this table should be recalculated as follows.
> *Original ValidWriteIdList:* \{hwm=10, open/aborted=5,6} – (10 is allocated
> by txn < current txn_id).
> *Allocated writeId for this txn:* 13 – (11 and 12 are taken by some other txn
> > current txn_id)
> *New ValidWriteIdList:* \{hwm=12, open/aborted=5,6,11, 12} – (11, 12 are
> added to invalid list, so the snapshot remains same).
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