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From "Sankar Hariappan (JIRA)" <>
Subject [jira] [Updated] (HIVE-18747) Cleaner for TXN_TO_WRITE_ID table entries.
Date Tue, 20 Feb 2018 08:28:00 GMT


Sankar Hariappan updated HIVE-18747:
    Summary: Cleaner for TXN_TO_WRITE_ID table entries.  (was: Cleaner for TXNS_TO_WRITE_ID
table entries.)

> Cleaner for TXN_TO_WRITE_ID table entries.
> ------------------------------------------
>                 Key: HIVE-18747
>                 URL:
>             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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