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From Dan Washusen <...@reactive.org>
Subject Re: I: Re: Are row-keys sorted by the compareWith?
Date Wed, 23 Feb 2011 21:44:10 GMT
Hi Matthew,
As you mention the map returned from multiget_slice is not order preserving, Pelops is doing
this on the client side...

Cheers,
Dan

-- 
Dan Washusen
Sent with Sparrow
On Wednesday, 23 February 2011 at 8:38 PM, Matthew Dennis wrote: 
> The map returned by multiget_slice (what I suspect is the underlying thrift call for
getColumnsFromRows) is not a order preserving map, it's a HashMap so the order of the returned
results cannot be depended on.  Even if it was a order preserving map, not all languages would
be able to make use of the results since not all languages have ordered maps (though many,
including Java, certainly do).
> 
> That being said, it would be fairly easy to change this on the C* side to preserve the
order the keys were requested in, though as mentioned not all clients could take advantage
of it.
> 
>  On Mon, Feb 21, 2011 at 4:09 PM, cbertu81@libero.it <cbertu81@libero.it> wrote:
> > > 
> > > 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).
> > > 
> > > Thanks for your answer and for your time, I will take a look at this.
> > > 
> > > 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). 
> > > 
> > > mmm ... well it didn't happen like this. In my code I had a CF named comments
and also a CF called usercomments. UserComments use an uuid as row-key to keep, TimeUUID sorted,
the "pointers" to the comments of the user. When I get the sorted list of keys from the UserComments
and I use this list as row-keys-list in the GetColumnsFromRows I don't get back the data sorted
as I expect them to be. 
> > > It looks like if Cassandra/Pelops does not care on how I provide the row-keys-list.
I am sure about that cause I did something different: I iterate over my row-keys-list and
made many GetColumnFromRow instead of one GetColumnsFromRows and when I iterate data are correctly
sorted. But this can not be a solution ...
> > > 
> > > I am using Cassandra 0.6.9
> > > 
> > > I profit of your knownledge of Pelops to ask you something: I am evaluating
the migration to Cassandra 0.7 ... as far as you know, in terms of written code, is it an
heavy job? 
> > > 
> > > Best Regards
> > > 
> > > Carlo
> > > 
> > > >  ----Messaggio originale----
> > > >  Da: dan@reactive.org
> > > > 
> > > > 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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