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https://issues.apache.org/jira/browse/HIVE-18864?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16397469#comment-16397469
 ] 

Sankar Hariappan edited comment on HIVE-18864 at 3/13/18 6:56 PM:
------------------------------------------------------------------

String s = "select t2w_txnid, t2w_writeid from TXN_TO_WRITE_ID where t2w_txnid 
<= " + txnHwm
               + " and t2w_database = " + quoteString(names[0])
               + " and t2w_table = " + quoteString(names[1])
               + " order by t2w_writeid asc";
 In this query, we fetch the list of write ids allocated by txns <= txnHwm...

In my example, writeId=7 is allocated by txnId=txnHwm, but 6 was allocated by 
txnId > txnHwm... So, it won't be listed by this query and hence writeId=6 will 
never make it to the open list


was (Author: sankarh):
String s = "select t2w_txnid, t2w_writeid from TXN_TO_WRITE_ID where t2w_txnid 
<= " + txnHwm
              + " and t2w_database = " + quoteString(names[0])
              + " and t2w_table = " + quoteString(names[1])
              + " order by t2w_writeid asc";
In this query, we fetch the list of write ids allocated by txns <= txnHwm... In 
my example, writeId=7 is allocated by txnId=txnHwm, but 6 was allocated by 
txnId > txnHwm... So, it won't be listed by this query and hence writeId=, 
never make it to the open list

> ValidWriteIdList snapshot seems incorrect if obtained after allocating 
> writeId by current transaction.
> ------------------------------------------------------------------------------------------------------
>
>                 Key: HIVE-18864
>                 URL: https://issues.apache.org/jira/browse/HIVE-18864
>             Project: Hive
>          Issue Type: Sub-task
>          Components: Transactions
>    Affects Versions: 3.0.0
>            Reporter: Sankar Hariappan
>            Assignee: Sankar Hariappan
>            Priority: Major
>              Labels: ACID, pull-request-available
>             Fix For: 3.0.0
>
>         Attachments: HIVE-18864.01.patch, HIVE-18864.02.patch
>
>
> For multi-statement txns, it is possible that write on a table happens after 
> a read. Let's see the below scenario.
>  # Committed txn=9 writes on table T1 with writeId=5.
>  # Open txn=10. ValidTxnList(open:null, txn_HWM=10),
>  # Read table T1 from txn=10. ValidWriteIdList(open:null, write_HWM=5).
>  # Open txn=11, writes on table T1 with writeid=6.
>  # Read table T1 from txn=10. ValidWriteIdList(open:null, write_HWM=5).
>  # Write table T1 from txn=10 with writeId=7.
>  # Read table T1 from txn=10. {color:#d04437}*ValidWriteIdList(open:null, 
> write_HWM=7)*. – This read will able to see rows added by txn=11 which is 
> still open.{color}
> {color:#d04437}So, it is needed to rebuild the open/aborted list of 
> ValidWriteIdList based on txn_HWM. Any writeId allocated by txnId > txn_HWM 
> should be marked as open. In this example, *ValidWriteIdList(open:6, 
> write_HWM=7)* should be generated.{color}
> {color:#333333}cc{color} [~ekoifman], [~thejas]



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