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Posted to issues@hive.apache.org by "Sankar Hariappan (JIRA)" <ji...@apache.org> on 2018/02/20 08:22:00 UTC

[jira] [Assigned] (HIVE-18747) Cleaner for TXNS_TO_WRITE_ID table entries.

     [ https://issues.apache.org/jira/browse/HIVE-18747?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Sankar Hariappan reassigned HIVE-18747:
---------------------------------------


> 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
>            Priority: Minor
>              Labels: ACID, replication
>             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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