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https://issues.apache.org/jira/browse/HIVE-18747?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Eugene Koifman updated HIVE-18747:
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Summary: Cleaner for TXN_TO_WRITE_ID table entries/MIN_HISTORY_LEVEL.
(was: Cleaner for TXN_TO_WRITE_ID table entries.)
> Cleaner for TXN_TO_WRITE_ID table entries/MIN_HISTORY_LEVEL.
> ------------------------------------------------------------
>
> Key: HIVE-18747
> URL: https://issues.apache.org/jira/browse/HIVE-18747
> Project: Hive
> Issue Type: Sub-task
> Components: Transactions
> Affects Versions: 3.0.0
> Reporter: Sankar Hariappan
> Assignee: Sankar Hariappan
> Priority: Minor
> Labels: ACID
> 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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