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From Himanshu Vashishtha <hvash...@cs.ualberta.ca>
Subject Re: Scan.addFamiliy reduces results
Date Thu, 15 Mar 2012 18:42:45 GMT
" Let's also say there are 1000 rows with A,B,C and 500 rows with only B and C.

If I add families A, B and C and scan with no filter will I get 1500,
1000 or 500 results?"

In this case, you will get 1000 rows. In case you add only B, you will
get 500 rows.

It's not like if you add families A, B and C, it will give you _only_
those rows that have _all_ three families; rather it will give all
rows that contain _any_ of these families.

Hope this helps.

Experts are welcome to chime in if I am missing something :)

Thanks,
Himanshu


On Thu, Mar 15, 2012 at 11:48 AM, Peter Wolf <opus111@gmail.com> wrote:
> Hi Lars, still confused...
>
> My table *should* have values for families A, B and C.  Let's say I have a
> bug, and some rows only have values for B and C.  Let's also say there are
> 1000 rows with A,B,C and 500 rows with only B and C.
>
> If I add families A, B and C and scan with no filter will I get 1500, 1000
> or 500 results?
>
> Many thanks
> P
>
>
>
>
> On 3/15/12 1:17 PM, lars hofhansl wrote:
>>
>> Hi haijia,
>>
>> In that case HBase will still return the data for columns in family B and
>> C.But if you only added family A then HBase would only return "rows" for
>> which family A has any columns.
>>
>> -- Lars
>> ________________________________
>>
>> From: Haijia Zhou<leonster@gmail.com>
>> To: user@hbase.apache.org; lars hofhansl<lhofhansl@yahoo.com>
>> Sent: Thursday, March 15, 2012 10:12 AM
>> Subject: Re: Scan.addFamiliy reduces results
>>
>>
>> I have the same confusion. Say if I added three column families A, B anc C
>> to the scan, now if a row has data for column family B and C but no data for
>> A, then it won't be returned  in the next() method?
>> What if the requirement is to get row data regardless of whether there's
>> data for a specific column family or not?
>>
>>
>> On Thu, Mar 15, 2012 at 1:04 PM, lars hofhansl<lhofhansl@yahoo.com>
>>  wrote:
>>
>> Hi Peter,
>>>
>>> for HBase you have keep in mind that it is a sparse columnar (or
>>> KeyValue) store: (rowkey, columnfamily, column, TS) ->  value
>>>
>>> A scan only returns those KeyValues that match the scan. So when you set
>>> families on your scan you'll only get those rows for which the scan found
>>> any columns.
>>>
>>> Makes sense?
>>>
>>> -- Lars
>>>
>>>
>>>
>>> ________________________________
>>>  From: Peter Wolf<opus111@gmail.com>
>>> To: user@hbase.apache.org
>>> Sent: Thursday, March 15, 2012 9:52 AM
>>> Subject: Re: Scan.addFamiliy reduces results
>>>
>>>
>>> Thanks Doug,
>>>
>>> I had read that, and I just read it again.  But I am missing something...
>>>
>>> Why does adding a family reduce the number of results?  Is there an
>>> implied filter of some form?  Does addFamily add some constraint on
>>> which rows are returned?
>>>
>>> Note that all my rows *ought* to have values in all the families.
>>>
>>> Thanks
>>> Peter
>>>
>>> On 3/15/12 12:39 PM, Doug Meil wrote:
>>>>
>>>> re:  "However, I am getting different number of results, depending on
>>>> which families are added"
>>>>
>>>> Yes.
>>>>
>>>> I'd suggest you read this in the RefGuide.
>>>>
>>>> http://hbase.apache.org/book.html#datamodel
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> On 3/15/12 12:08 PM, "Peter Wolf"<opus111@gmail.com>   wrote:
>>>>
>>>>> Hi all,
>>>>>
>>>>> I am doing a scan on a table with multiple families.  My code looks
>>>>> like
>>>>> this...
>>>>>
>>>>>           Scan scan = new Scan(calculateStartRowKey(a),
>>>>> calculateEndRowKey(b));
>>>>>
>>>>>           scan.setCaching(10000);
>>>>>           Filter filter = new SingleColumnValueFilter(xFamily, xColumn,
>>>>> CompareFilter.CompareOp.EQUAL, Bytes.toBytes(x));
>>>>>           scan.setFilter(filter);
>>>>>           scan
>>>>>                   .addFamily(xFamily)
>>>>>                   .addFamily(yFamily)
>>>>>                   .addFamily(zFamily);
>>>>>
>>>>>           ResultScanner scanner = hTable.getScanner(scan);
>>>>>
>>>>>           Iterator<Result>   it = scanner.iterator();
>>>>>           int resultCount = 0;
>>>>>           while (it.hasNext()) {
>>>>>                 Result result = it.next();
>>>>>
>>>>>                 resultCount++;
>>>>>           }
>>>>>
>>>>> However, I am getting different number of results, depending on which
>>>>> families are added.  For example these give different result counts
>>>>>
>>>>>           scan
>>>>>                   //.addFamily(xFamily)
>>>>>                   .addFamily(yFamily)
>>>>>                   .addFamily(zFamily);
>>>>> and
>>>>>           scan
>>>>>                   .addFamily(xFamily)
>>>>>                   .addFamily(yFamily)
>>>>>                   .addFamily(zFamily);
>>>>>
>>>>>
>>>>> There is no error message, and I don't see anything in the Scan
>>>>> documentation.  Does anyone know what is going on?
>>>>>
>>>>> Thanks
>>>>> Peter
>>>>>
>>>>>
>>>>>
>

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