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https://issues.apache.org/jira/browse/HIVE-14427?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15435409#comment-15435409
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Barna Zsombor Klara commented on HIVE-14427:
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Here is my take at it:
https://reviews.apache.org/r/51381/
> CompactionTxnHandler.markCleaned() can delete aborted txns
> ----------------------------------------------------------
>
> Key: HIVE-14427
> URL: https://issues.apache.org/jira/browse/HIVE-14427
> Project: Hive
> Issue Type: Improvement
> Components: Transactions
> Reporter: Eugene Koifman
>
> We can modify
> {noformat}
> s = "select distinct txn_id from TXNS, TXN_COMPONENTS where txn_id = tc_txnid
> and txn_state = '" +
> TXN_ABORTED + "' and tc_database = '" + info.dbname + "' and
> tc_table = '" +
> info.tableName + "'" + (info.highestTxnId == 0 ? "" : " and txn_id
> <= " + info.highestTxnId);
> {noformat}
> to use select txn_id, count(*) ... group by txn_id so that we know the number
> of components in a TXN.
> Then when running "delete from TXN_COMPONENTS where..." we know how many rows
> were deleted.
> If the sum of all values from 1st query matched total number of rows deleted,
> we know that all Aborted txns in this set are empty and thus can be deleted
> here.
> This means we clean up aborted txns from TXNS table quicker and avoid a large
> join in _cleanEmptyAbortedTxns()_. Also, doing delete on TXNS here will have
> PKs in WHERE clause so it should be cheap.
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