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From "Mass Dosage (JIRA)" <>
Subject [jira] [Created] (HIVE-15965) Metastore incorrectly re-uses a broken database connection
Date Fri, 17 Feb 2017 11:09:41 GMT
Mass Dosage created HIVE-15965:

             Summary: Metastore incorrectly re-uses a broken database connection
                 Key: HIVE-15965
             Project: Hive
          Issue Type: Bug
          Components: Metastore
    Affects Versions: storage-2.2.0
            Reporter: Mass Dosage

In our setup we have a shared standalone MetaStore server running on EMR that is accessed
by various clients (Hive CLI, HiveServer2, Spark etc.) and connects to an external MariaDB
database for the MetaStore DB. It came to our attention that MetaStore (or rather the underlying
DataNucleus / BoneCP combo) will keep re-using the same DB connections even when those get
suddenly closed for a reason that renders them unusable.

For instance, due to a bug in the MariaDB JDBC driver v1.3.6 (see,
a huge query including over 8 thousand parameter placeholders (e.g. partition IDs in case
of a {{get_partitions_by_expr}} function call)
will yield a {{java.nio.BufferOverflowException}} and cause the SQL connection be closed by
the driver itself.

This will ultimately result in the abortion of all further MetaStore Thrift calls due to the
failure of {{bonecp.ConnectionHandle.prepareStatement()}}.

Such scenarios will be then caught by DataNucleus and translated to an appropriate {{JDOException}},
only to be "ignored" by the MetaStore.{{RetryingHMSHandler}} will, of course, continue retrying
the failing operation, but this is already pointless by that time since they will invariably
fail as long as the SQL connection remains closed. Please see the attached MetaStore log [^hive.log]
for details

(captured from Hive 2.1.1 running on Windows in Eclipse IDE).

 *Proposed behavior*

We suggest that MetaStore should automatically renew the DB connection whenever:

* The connection gets closed by one of the underlying frameworks (DataNucleus, BoneCP, JDBC
driver); or
* Query timeout is detected.

This feature should be optional and configurable (disabled by default for backward compatibility).
Reconnection failures could probably be treated as fatal errors and cause the immediate termination
of MetaStore.

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