[jira] [Created] (HIVE-18923) ValidWriteIdList snapshot per table can be cached for multi-statement transactions.

["Sankar Hariappan (JIRA)" <ji...@apache.org>]

Sankar Hariappan created HIVE-18923:
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             Summary: 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: Sub-task
          Components: Transactions
    Affects Versions: 3.0.0
            Reporter: Sankar Hariappan
            Assignee: Sankar Hariappan
             Fix For: 3.0.0


Currently, for each query within a multi-statement transaction, it would request metastore/TxnHandler to build ValidWriteIdList snapshot for the given table. But, the snapshot won't change within the duration of transaction. So, it make sense to cache it within QueryTxnManager.

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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