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From "Kevin Wilfong (JIRA)" <>
Subject [jira] [Created] (HIVE-3826) Rollbacks and retries of drops cause org.datanucleus.exceptions.NucleusObjectNotFoundException: No such database row)
Date Thu, 20 Dec 2012 21:41:12 GMT
Kevin Wilfong created HIVE-3826:

             Summary: Rollbacks and retries of drops cause org.datanucleus.exceptions.NucleusObjectNotFoundException:
No such database row)
                 Key: HIVE-3826
             Project: Hive
          Issue Type: Bug
          Components: Metastore
    Affects Versions: 0.11
            Reporter: Kevin Wilfong
            Assignee: Kevin Wilfong

I'm not sure if this is the only cause of the exception "org.datanucleus.exceptions.NucleusObjectNotFoundException:
No such database row)" from the metastore, but one cause seems to be related to a drop command
failing, and being retried by the client.

Based on focusing on a single thread in the metastore with DEBUG level logging, I was seeing
the objects that were intended to be dropped remaining in the PersistenceManager cache even
after a rollback.  The steps seemed to be as follows:

1) First attempt to drop the table, the table is pulled into the PersistenceManager cache
for the purposes of dropping
2) The drop fails, e.g. due to a lock wait timeout on the SQL backend, this causes a rollback
of the transaction
3) The drop is retried using a different thread on the metastore Thrift server or a different
server and succeeds
4) Back on the original thread of the original Thrift server someone tries to perform some
write operation which produces a commit.  This causes those detached objects related to the
dropped table to attempt to reattach, causing JDO to query the SQL backend for those objects
which it can't find.  This causes the exception.

I was able to reproduce this regularly using the following sequence of commands:
Hive client 1 (Hive1): connected to a metastore Thrift server running a single thread, I hard
coded a RuntimeException into the code to drop a table in the ObjectStore, specifically right
before the commit in preDropStorageDescriptor, to induce a rollback
Hive client 2 (Hive2): connected to a separate metastore Thrift server running with standard
configs and code

1: On Hive1, CREATE TABLE t1 (c STRING);
2: On Hive1, DROP TABLE t1; // This failed due to the hard coded exception
3: On Hive2, DROP TABLE t1; // Succeeds
4: On Hive1, CREATE DATABASE d1; // This database already existed, I'm not sure why this was
necessary, but it didn't work without it, it seemed to have an affect on the order objects
were committed in the next step
5: On Hive1, CREATE DATABASE d2; // This database didn't exist, it would fail with the NucleusObjectNotFoundException

The object that would cause the exception varied, I saw the MTable, the MSerDeInfo, and MTablePrivilege
from the table that attempted to be dropped.

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