SV: SV: Help with getting Key range with some column limitations

[Thorvaldsson Justus]

I think you should try to do it some other way than iterate, it sounds super 
suboptimal to me. Also the plugin option he was thinking of I think is changing 
Cassandra sourcecode, kind of hard when Cassandra is changing so fast but very 
possible. I think you should look at http://blip.tv/file/4015273 and perhaps my 
blog post about the same thing at www.Justus.st<http://www.Justus.st> Cassandra 
post 4 more on Data model

Exampel code in java, start and end key, next iteration the end should be the 
last key that you collected, depends how you made you model
//Keyrange is for what row key, you can specify what row startkey,endkey and 
how many rows
KeyRange keyRange = new KeyRange(700);
keyRange.setStart_key(rowId);
keyRange.setEnd_key(rowId);

 //Specify what supercolumns you want to get
SliceRange sliceRange = new SliceRange();
sliceRange.setStart(new byte[] {});
sliceRange.setFinish(new byte[] {});

/J

Från: Jone Lura [mailto:jone.l...@ecc.no]
Skickat: den 20 augusti 2010 08:53
Till: user@cassandra.apache.org
Ämne: Re: SV: Help with getting Key range with some column limitations

Thanks for you suggestions.

I tried to iterate them, however I could not get it to work (pretty sure its my 
code). Im still not to familiar with Cassandra, so could you provide a small 
example?

The key count could be up to atleast 20k and maybe more, and users should not 
wait for more than 10 seconds for their map, so I also want to investigate the 
plugin suggestion. Does the plugin exist? or do I have to develop it myself? 
Are there any documentation on plugin development for Cassandra?

Best regards

Jone


On 19/08/2010 08:42, Thorvaldsson Justus wrote:
You should iterate through them, get 200 then go get the next 200 and so on.
Also if checking a bounding box to another.. perhaps try sorting them so you 
could start looking at both ends, perhaps make the iteration smaller until 
match somehow?
Just my simple coins, also upgrading will probably be needed to iterate through 
RP because of bugs. But that should be simple enough to 6.4
/Justus

Från: Jone Lura [mailto:jone.l...@ecc.no]
Skickat: den 18 augusti 2010 20:32
Till: user@cassandra.apache.org<mailto:user@cassandra.apache.org>
Ämne: Help with getting Key range with some column limitations

Hi,

We are trying to implement Cassandra to replace one of our biggest SQL tables, 
and so far we got it working.

However, for testing I'm using Cassandra 0.6.2, Java and Pelops. (Pelops not 
that important for my question) and need suggestions on how to solve a problem 
retrieving a key range based on the following.

<Keyspace Name="AIS">
        <ColumnFamily Name="Location"
        ColumnType="Super"
        CompareWith="LongType"
        KeysCached="100%"
        CompareSubcolumnsWith="UTF8Type" />
     ...
    </Keyspace>

The super column got columns for longitude and latitude.

 1. Need to get get max long number for key
 2. The key should also have supercolumns latitude and longitude column 
intersecting (inside) with a given boundingbox.

Currently I'm doing like this


        KeyRange keyRange = new KeyRange();
        keyRange.setStart_key("");
        keyRange.setEnd_key("");
        keyRange.setCount(700);

And checking every row in db if it match my bounding box.

But there are a lot more than 700 keys.. and if i set a higher count, the 
get_range_slice get a Timeout Exception.

Any ideas?

Best Regards
Jone