[jira] [Commented] (HIVE-21114) Create read-only transactions

["Vaibhav Gumashta (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HIVE-21114?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16793407#comment-16793407 ] 

Vaibhav Gumashta commented on HIVE-21114:
-----------------------------------------

cc [~pvary]  [~anishek] 

This will also be useful for the Hive Replication effort to limit the overhead so that read only txns need not be replicated on the target.

> Create read-only transactions
> -----------------------------
>
>                 Key: HIVE-21114
>                 URL: https://issues.apache.org/jira/browse/HIVE-21114
>             Project: Hive
>          Issue Type: Bug
>          Components: Transactions
>    Affects Versions: 4.0.0
>            Reporter: Eugene Koifman
>            Assignee: Igor Kryvenko
>            Priority: Major
>
> With HIVE-21036 we have a way to indicate that a txn is read only.
> We should (at least in auto-commit mode) determine if the single stmt is a read and mark the txn accordingly.  
> Then we can optimize {{TxnHandler.commitTxn()}} so that it doesn't do any checks in write_set etc.
> {{TxnHandler.commitTxn()}} already starts with {{lockTransactionRecord(stmt, txnid, TXN_OPEN)}} so it can read the txn type in the same SQL stmt.
> HiveOperation only has QUERY, which includes Insert and Select, so this requires figuring out how to determine if a query is a SELECT.  By the time {{Driver.openTransaction();}} is called, we have already parsed the query so there should be a way to know if the statement only reads.
> For multi-stmt txns (once these are supported) we should allow user to indicate that a txn is read-only and then not allow any statements that can make modifications in this txn.  This should be a different jira.
> cc [~ikryvenko]



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