[HIVE-18864] ValidWriteIdList snapshot seems incorrect if obtained after allocating writeId by current transaction.

• Type: Sub-task
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 3.0.0
• Fix Version/s: 3.0.0
• Component/s: Transactions
• Labels: ACID pull-request-available
• Assignee: Sankar Hariappan
• Reporter: Sankar Hariappan
• Created: 05/Mar/18 19:50
• Updated: 22/May/18 23:13
• Resolved: 13/Mar/18 20:26

Description

For multi-statement txns, it is possible that write on a table happens after a read. Let's see the below scenario.

1. Committed txn=9 writes on table T1 with writeId=5.
2. Open txn=10. ValidTxnList(open:null, txn_HWM=10),
3. Read table T1 from txn=10. ValidWriteIdList(open:null, write_HWM=5).
4. Open txn=11, writes on table T1 with writeid=6.
5. Read table T1 from txn=10. ValidWriteIdList(open:null, write_HWM=5).
6. Write table T1 from txn=10 with writeId=7.
7. Read table T1 from txn=10. ValidWriteIdList(open:null, write_HWM=7). – This read will able to see rows added by txn=11 which is still open.

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.

cc ekoifman, thejas

Issue Links

• is related to: HIVE-18192 Introduce WriteID per table rather than using global transaction ID
• links to: GitHub Pull Request #316