Sqoop ExportTool to Oracle NullPointer Exception - oracle

Question

Using command like:
sqoop export \
--connect jdbc:oracle:thin:'#somehostname.com:1521/prod1_adhoc' \
--username fbaggins \
--P \
--table MIDDLEEARTH \
--hcatalog-database MORDOR \
--hcatalog-table MORDOR \
--columns IS_DWARF,IS_ELF \
--verbose
Results in this error:
16/08/25 10:08:31 INFO hive.metastore: Trying to connect to metastore with URI thrift://somehostname.com:1521
16/08/25 10:08:31 INFO hive.metastore: Connected to metastore.
16/08/25 10:08:31 DEBUG util.ClassLoaderStack: Restoring classloader: sun.misc.Launcher$AppClassLoader#56aac163
16/08/25 10:08:31 ERROR tool.ExportTool: Encountered IOException running export job: java.io.IOException: java.lang.NullPointerException
16/08/25 10:08:31 DEBUG manager.OracleManager$ConnCache: Caching released connection for jdbc:oracle:thin:#somehostname.com:1521/prod1_adhoc/fbaggins
Not sure where the null is coming from as there are no nulls in the Hive table.
For reference, from hive:
hive> describe MORDOR;
OK
IS_DWARF bigint
IS_ELF string
From Oracle:
describe MORDOR
Name Null Type
----------------------- ---- -----------
IS_DWARF NUMBER(12)
IS_ELF VARCHAR2(3)

Answer 1

Is MORDOR a Hive view and not actually a table?
I have exactly the same problem when an object specified for sqoop --table is a view. DESCRIBE commands just prints columns of that view - so it does not show if it's a view or not. You could run SHOW CREATE TABLE MORDOR to confirm that's a view or table ("show create table" works for a view too as there is no separate command like "show create view").
SQOOP documentation explicitly states that sqoop import from a view is supported, but sqoop documentation on sqoop export for a view is silent - it's not stated if it's supported or not - it might be a SQOOP or HMS bug. Sqoop might not like what HMS returns for a view. So not exluding it might be an HMS bug.

Answer 2

Look at the logs again: don't you see anything absurd?
Trying to connect to metastore with URI thrift://$HOSTNAME:$PORT
Caching released connection for jdbc:oracle:thin:#$HOST:$PORT/$ALIAS/$SCHEMA
Yes. The bloody environment variables (or shell variables) have not been resolved by the shell. Although I'm not sure what happened to the Metastore URI (it's defined in a Hadoop conf file, no shell/env variables there...)
That's because you have enclosed them in SINGLE QUOTES.
--connect jdbc:oracle:thin:'#$HOST:$PORT/$ALIAS'
So you have a 3-step solution:
use double quotes whenever you want the shell to resolve variables inside
learn script shell
learn about pointers, Null pointers, and what happens when some buggy code fails to check whether an Object variable has been properly initialized (i.e. NullPointerException in Java)