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From "cbertu81@libero.it" <cbert...@libero.it>
Subject R: Re: Are row-keys sorted by the compareWith?
Date Mon, 21 Feb 2011 22:08:02 GMT
Sorry Dan, I just noticed I answer you and not to the group!Didn't want to bother, just mistake.
Best Regards
Carlo


----Messaggio originale----

Da: dan@reactive.org

Data: 21/02/2011 4.23

A: <user@cassandra.apache.org>, "cbertu81@libero.it"<cbertu81@libero.it>

Ogg: Re: Are row-keys sorted by the compareWith?




            
                Hi Carlo,As Jonathan mentions the compareWith on a column family def. is defines
the order for the columns *within* a row... In order to control the ordering of rows you'll
need to use the OrderPreservingPartitioner (http://www.datastax.com/docs/0.7/operations/clustering#tokens-partitioners-ring).
As for getColumnsFromRows; it should be returning you a map of lists.  The map is insertion-order-preserving
and populated based on the provided list of row keys (so if you iterate over the entries in
the map they should be in the same order as the list of row keys).  The list for each row
entry are definitely in the order that Cassandra provides them, take a look at org.scale7.cassandra.pelops.Selector#toColumnList
if you need more info.
Cheers,Dan
                
-- 
Dan Washusen
Sent with Sparrow

                
                On Saturday, 19 February 2011 at 8:16 AM, cbertu81@libero.it wrote:
                
                    Hi all,
I created a CF in which i need to get, sorted by time, the Rows inside. Each 
Row represents a comment.

<ColumnFamily name="Comments" compareWith="TimeUUIDType" / >

I've created a few rows using as Row Key a generated TimeUUID but when I call 
the Pelops method "GetColumnsFromRows" I don't get the data back as I expect: 
rows are not sorted by TimeUUID.
I though it was probably cause of the random-part of the TimeUUID so I create 
a new CF ...

<ColumnFamily name="Comments2" compareWith="LongType" / >

This time I created a few rows using the java System.CurrentTimeMillis() that 
retrieve a long. I call again the "GetColumnsFromRows" and again the same 
results: data are not sorted!
I've read many times that Rows are sorted as specified in the compareWith but 
I can't see it. 
To solve this problem for the moment I've used a SuperColumnFamily with an 
UNIQUE ROW ... but I think this is just a workaround and not the solution.

<ColumnFamily name="Comments" type="Super" compareWith="TimeUUIDType"  
CompareSubcolumnsWith="BytesType"/ >

Now when I call the "GetSuperColumnsFromRow" I get all the SuperColumns as I 
expected: sorted by TimeUUID. Why it does not happen the same with the Rows? 
I'm confused.

TIA for any help.

Best Regards

Carlo

                
                
                
                
                
                
                
                    

                
            
        




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