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From "Jim Kellerman (JIRA)" <j...@apache.org>
Subject [jira] Created: (HBASE-1774) HTable$ClientScanner modifies its input parameters
Date Tue, 18 Aug 2009 02:39:14 GMT
HTable$ClientScanner modifies its input parameters

                 Key: HBASE-1774
                 URL: https://issues.apache.org/jira/browse/HBASE-1774
             Project: Hadoop HBase
          Issue Type: Bug
          Components: client
    Affects Versions: 0.20.0
            Reporter: Jim Kellerman
            Assignee: Jim Kellerman
            Priority: Critical

HTable$ClientScanner modifies the Scan that is passed to it on construction.

I would consider this to be bad programming practice because if I wanted to use the same Scan
object to scan multiple tables, I would not expect one table scan to effect the other, but
it does.

If input parameters are going to be modified either now or later it should be called out *loudly*
in the javadoc. The only way I found this behavior was by creating an application that did
scan multiple tables using the same Scan object and having 'wierd stuff' happen.

In my opinion, if you want to modify a field in an input parameter, you should:
- make a copy of the original object
- optionally return a reference to the copy.

There is no javadoc about this behavior. The only thing I found was a comment in HTable$ClientScanner:
    // HEADSUP: The scan internal start row can change as we move through table.

Is there a use case that requires this behavior? If so, I would recommend that ResultScanner
 (and the classes that implement it) provide an accessor to the mutable copy of the input
Scan and leave the input argument alone.

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