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: d...@reactive.org
On Saturday, 19 February 2011 at 8:16 AM, cbert...@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
