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https://issues.apache.org/jira/browse/HIVE-18747?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16402028#comment-16402028
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ASF GitHub Bot commented on HIVE-18747:
---------------------------------------
GitHub user sankarh opened a pull request:
https://github.com/apache/hive/pull/321
HIVE-18747: Cleaner for TXN_TO_WRITE_ID table entries/MIN_HISTORY_LEVEL.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/sankarh/hive HIVE-18747
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/hive/pull/321.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #321
----
commit 3cba53bbf711dd6ea17c271c38c7fb6aefb17925
Author: Sankar Hariappan <mailtosankarh@...>
Date: 2018-03-12T20:58:53Z
HIVE-18747: Cleaner for TXN_TO_WRITE_ID table entries/MIN_HISTORY_LEVEL.
----
> 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, pull-request-available
> 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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