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Sankar Hariappan commented on HIVE-18864: ----------------------------------------- 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] -- This message was sent by Atlassian JIRA (v7.6.3#76005)