Hive queries were getting stuck/hang on both mr and tez engines while selecting from a table containing few csv files.
While the query was working fine for few csv files, for others it just hangs. Nothing in the logs also.
I was using Hive 1.2.1 on HDP 18.104.22.168
After some investigation, I found out that those files have some empty values '' in the fields where an rpad function was getting used.
You can easily reproduce the issue by firing:
You will see that the query just hangs.
The reason is it goes to an infinite loop.
More details here: HIVE-15792
nvl will not work in this case.
select nvl('','D'); --will return ''
I resolved using a query like this:
SELECT rpad(CASE WHEN LENGTH(nvl(COLUMN_NAME,null)) > 0 THEN COLUMN_NAME ELSE null END, 1, '');
In this case the query will return null for both null and empty string values occurring in COLUMN_NAME.
Hope this helps.