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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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Sankar Hariappan updated HIVE-18747:
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Description:
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 (highest txn <=
min_uncommitted_txn) per table to mark as LWM (low water mark).
was:
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 (highest committed txn) per
table to mark as LWM (low water mark).
> Cleaner for TXN_TO_WRITE_ID table entries using 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
>
> Attachments: HIVE-18747.01.patch
>
>
> 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 (highest txn <=
> min_uncommitted_txn) per table to mark as LWM (low water mark).
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