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https://issues.apache.org/jira/browse/HIVE-21114?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16954482#comment-16954482
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Denys Kuzmenko commented on HIVE-21114:
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Currently we support only single stmt transactions and allocate transaction id
per stmt, supported isolation level is SHAPSHOT.
Scenario when we might misclassify the transaction could be when using
some_func() with DML operation inside, however I am not sure if procedural
language support was introduced in Hive.
We also introduced an assertion based on writeTables to verify that we haven't
misclassified the transaction.
Having read-only attr would be beneficial for a number of transaction
optimisations like HIVE-21226.
> 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: Denys Kuzmenko
> Priority: Major
> Attachments: HIVE-21114.1.patch, HIVE-21114.2.patch,
> HIVE-21114.3.patch, HIVE-21114.4.patch, HIVE-21114.5.patch,
> HIVE-21114.6.patch, HIVE-21114.7.patch
>
>
> 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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