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From Thorvaldsson Justus <justus.thorvalds...@svenskaspel.se>
Subject SV: SV: SV: Help with getting Key range with some column limitations
Date Fri, 20 Aug 2010 08:48:13 GMT
If you only want to check the last 5 min, make time a part of your key
And make a customized sort and sort by the time. Remember sort is made when inserting data.
http://www.sodeso.nl/?p=421
Or make a range check that understands the time limit, should work I think from the top of
my head.

But you don't want a lot of small rows and also not to fat rows so..
Perhaps there is some time limit that could be rowed
And sc is long&lat and you can figure a way to make a range check on one of them if they
arnt to many perhaps It would work.
/J
There are so many opportunities to model that you probably want to make several and test them

Från: Jone Lura [mailto:jone.lura@ecc.no]
Skickat: den 20 augusti 2010 10:37
Till: user@cassandra.apache.org
Ämne: Re: SV: SV: Help with getting Key range with some column limitations

Thanks! Read your blog a few times, but it's hard to get rid of sql thinking.

So if I create a new standard ColumnFamily with a rowId and geohash a lat/lon into a UTF8Type,
I could geohash the boundingbox, and query for all matching columns. Or do I always need to
know the rowId to do a slicerange? I also need to only get the columns that are modified within
last 5 minutes.

Jone


On 20/08/2010 10:05, Thorvaldsson Justus wrote:
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.lura@ecc.no]
Skickat: den 20 augusti 2010 08:53
Till: user@cassandra.apache.org<mailto: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.lura@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">




        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



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