[jira] [Assigned] (HIVE-25113) Connection starvation in TxnHandler.getValidWriteIds

["Yu-Wen Lai (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HIVE-25113?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Yu-Wen Lai reassigned HIVE-25113:
---------------------------------


> Connection starvation in TxnHandler.getValidWriteIds
> ----------------------------------------------------
>
>                 Key: HIVE-25113
>                 URL: https://issues.apache.org/jira/browse/HIVE-25113
>             Project: Hive
>          Issue Type: Bug
>          Components: Transactions
>            Reporter: Yu-Wen Lai
>            Assignee: Yu-Wen Lai
>            Priority: Major
>
>  
> The current code looks like below.
> {code:java}
> dbConn = getDbConn(Connection.TRANSACTION_READ_COMMITTED);
> validTxnList = TxnUtils.createValidReadTxnList(getOpenTxns(), 0);
> {code}
> In the function getOpenTxns, it will request another connection from pool. That is, this thread already held a connection, however, it would request for another connection. When there are more than 10 (default connection pool size) simultaneous getValidWriteIds requests, it can cause a starvation problem. In that situation, each thread holds a connection and waits for another connection. Then, we will see the following exception after timeout.
> {code:java}
> metastore.RetryingHMSHandler: MetaException(message:Unable to select from transaction database, java.sql.SQLTransientConnectionException: HikariPool-3 - Connection is not available, request timed out after 30000ms.{code}
>  



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