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Posted to issues@hive.apache.org by "Sankar Hariappan (JIRA)" <ji...@apache.org> on 2018/03/06 17:30:00 UTC
[jira] [Commented] (HIVE-18864) ValidWriteIdList snapshot seems
incorrect if obtained after allocating writeId by current transaction.
[ https://issues.apache.org/jira/browse/HIVE-18864?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16388144#comment-16388144 ]
Sankar Hariappan commented on HIVE-18864:
-----------------------------------------
Attached 01.patch with changes in logic to build ValidWriteIdList.
# First find writeIdHwm based on txnHwm. This could be the writeId allocated by txnHwm itself or max(writeId) allocated by txnId<txnHwm.
# Now, get all txns with write Ids <= writeIdHwm.
## If any txnId >txnHwm, then move them to open/invalid list.
## If any txnId is marked open/aborted in ValidtxnList, then move them also to open/invalid list.
Request [~ekoifman] to take a look!
> 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
> Fix For: 3.0.0
>
> Attachments: HIVE-18864.01.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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