[jira] [Commented] (HIVE-18570) ACID IOW implemented using base may delete too much data

["Sergey Shelukhin (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HIVE-18570?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16424659#comment-16424659 ] 

Sergey Shelukhin commented on HIVE-18570:
-----------------------------------------

[~hagleitn] [~ashutoshc] [~ekoifman] I think this is another thing that needs to be addressed for ACID; although I guess current ACID behavior is still better than regular Hive tables.

> ACID IOW implemented using base may delete too much data
> --------------------------------------------------------
>
>                 Key: HIVE-18570
>                 URL: https://issues.apache.org/jira/browse/HIVE-18570
>             Project: Hive
>          Issue Type: Bug
>          Components: Transactions
>            Reporter: Sergey Shelukhin
>            Priority: Blocker
>             Fix For: 3.0.0
>
>
> Suppose we have a table with delta_0 insert data.
> Txn 1 starts an insert into delta_1.
> Txn 2 starts an IOW into base_2.
> Txn 2 commits.
> Txn 1 commits after txn 2 but its results would be invisible.
> Txn 2 deletes rows committed by txn 1 that according to standard ACID semantics it could have never observed and affected.
> If we treat IOW foo like DELETE FROM foo (to reason about it w.r.t. ACID semantics), it seems to me this sequence of events is only possible under read-uncommitted isolation level (so, 2 deletes rows written by 1).
> If 1 ran an update on rows instead of an insert, and 2 still ran an IOW/delete, row lock conflict (or equivalent) should cause one of them to fail.



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