Sankar Hariappan created HIVE-18747:
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Summary: Cleaner for TXNS_TO_WRITE_ID table entries.
Key: HIVE-18747
URL: https://issues.apache.org/jira/browse/HIVE-18747
Project: Hive
Issue Type: Sub-task
Components: repl, Transactions
Affects Versions: 3.0.0
Reporter: Sankar Hariappan
Assignee: Sankar Hariappan
Fix For: 3.0.0
Per table write ID implementation (HIVE-18192) maintains a map between txn ID
and table write ID in TXN_TO_WRITE_ID meta table.
The entries in this table is used to generate ValidWriteIdList for the given
ValidTxnList to ensure snapshot isolation.
When table or database is dropped, then these entries are cleaned-up. But, it
is necessary to clean-up for active tables too for better performance.
Need to have another table MIN_HISTORY_LEVEL to maintain the least txn which is
referred by any active ValidTxnList snapshot as open/aborted txn. If no
references found in this table for any txn, then it is eligible for cleanup.
After clean-up, need to maintain just one entry per table to mark as LWM (low
water mark).
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