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Date: Thu, 23 Feb 2012 15:04:26 -0500
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Subject: Re: Definition of Column Qualifier in User Manual
From: Keith Turner <keith@deenlo.com>
To: accumulo-user@incubator.apache.org
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One thing to consider when deciding if you want to use a column family
or qualifier is locality groups.  Column families can be placed in
locality groups.

On Thu, Feb 23, 2012 at 2:37 PM, David Medinets
<david.medinets@gmail.com> wrote:
> In this kind of situation, I've seen marker classes used so the intent
> of the parameter is clear. Marker classes also make it feasible to
> overload method signatures to allow for missing parameters.
>
> While you have explained using the empty string as a column qualifier,
> you haven't explained the column qualifier itself. I won't be
> misdirected so easily :)
>
> On Thu, Feb 23, 2012 at 11:55 AM, Adam Fuchs <adam.p.fuchs@ugov.gov> wrot=
e:
>> When we don't have an entry for an element of the key or the value we
>> typically use the empty string (or zero-length byte array). This is
>> technically different from null, but it seems to work well for all the u=
se
>> cases we've encountered so far. Here are some examples:
>>
>> =A0 =A0 Mutation m =3D new Mutation("david");
>> =A0 =A0 m.put("age","","23, no, really");
>>
>> =A0 =A0 Mutation m =3D new Mutation("david");
>> =A0 =A0 m.put("age","23, honest", "");
>>
>> =A0 =A0 byte[] empty =3D new byte[0];
>> =A0 =A0 Mutation m =3D new Mutation(new Text("david"));
>> =A0 =A0 m.put("age","23, honest",new Value(empty));
>>
>> The first example uses a zero-length column qualifier and populates the
>> value. The second and third examples result in exactly the same entries =
in
>> Accumulo, with a populated column qualifier and a zero-length value.
>>
>> Cheers,
>> Adam
>>
>>
>> On Wed, Feb 22, 2012 at 10:17 PM, David Medinets <david.medinets@gmail.c=
om>
>> wrote:
>>>
>>> Perhaps I've overlooked it, but I don't see a definition of Column
>>> Qualifier in the User Manual. Is there a best practice recommendation
>>> when the data is simply row,column,value (i.e., david,age,23). Can the
>>> qualifier or value be null?
>>
>>