incubator-cassandra-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Aaron Morton <aa...@thelastpickle.com>
Subject Re: Range Queries in RP on SCF in 0.7 with UUID SCs
Date Wed, 01 Dec 2010 23:16:27 GMT
When you say "I want to get rows starting from a Super Column..." it's a bit confusing. Do
you want to get super columns from a single row, or multiple rows? I'm assuming you are talking
about getting columns from a single row / key as that's what your code does.

For the pelops code, it looks OK but I've not used Pelops. You can turn the logging up on
the server and check the command that is sent to it. I'm would guess there is something wrong
with the way you are transforming the start key. 

For your cli example what was the command you executed ? 

Aaron

On 02 Dec, 2010,at 11:03 AM, Frank LoVecchio <frank@isidorey.com> wrote:

Hey Aaron, 

Yes, in regards to SCF definition, you are correct:  

name: Sensor
      column_type: Super
      compare_with: TimeUUIDType
      gc_grace_seconds: 864000
      keys_cached: 10000.0
      read_repair_chance: 1.0
      rows_cached: 0.0

I'm not quite sure I follow you, though, as I think I'm doing what you specify.  The Pelops
code is below.  Basically, I want to get rows starting from a Super Column with a specific
UUID and limit the number, just as you inferred.  When I run this code I just get the last
N values (25 in this case) if non-reversed, and the first N values if reversed.  However,
regardless of what start param we use (Super Column UUID is String startKey below), we still
get the same values for the specified amount (e.g. the same 25).  

public void getSuperRowKeys(String rowKey, String columnFamily, int limit, String startKey) throws Exception
{
	
		byte[] byteArray = UuidHelper.timeUuidStringToBytes(startKey);
		ByteBuffer bb = ByteBuffer.wrap(byteArray);
		new UUID (bb.getLong(), bb.getLong());
		
		
		List<SuperColumn> cols = selector.getPageOfSuperColumnsFromRow(columnFamily, rowKey,
Bytes.fromByteBuffer(bb), false, limit, ConsistencyLevel.ONE);

	
		for (SuperColumn col : cols) {
			if (col.getName() != null) {

				System.out.println("NAME: " + UUID.nameUUIDFromBytes(col.getName()));

				for (Column c : col.columns) {
					System.out.println("\t\tName: " + Bytes.toUTF8(c.getName())
							+ " Value: " + Bytes.toUTF8(c.getValue())
							+ " timestamp: " + c.timestamp);

				}

			}
		}

	}

Here is some example data from the CLI.  If we specify 2f814d30-f758-11df-2f81-4d30f75811df
as the start param (second super column down), we still get 52e6540-f759-11df-952e-6540f75911df
(first super column) returned.

=> (super_column=952e6540-f759-11df-952e-6540f75911df,
     (column=64617465, value=323031302d31312d32332032333a32393a30332e303030, timestamp=1290554997141000)
     (column=65787472615f696e666f, value=6e6f6e65, timestamp=1290554997141000)
     (column=726561736f6e, value=6e6f6e65, timestamp=1290554997141000)
     (column=7365636f6e64735f746f5f6e657874, value=373530, timestamp=1290554997141000)
     (column=73657269616c, value=393135353032353731, timestamp=1290554997141000)
     (column=737461747573, value=5550, timestamp=1290554997141000)
     (column=74797065, value=486561727462656174, timestamp=1290554997141000))
=> (super_column=2f814d30-f758-11df-2f81-4d30f75811df,
     (column=64617465, value=323031302d31312d32332032333a31393a30332e303030, timestamp=1290554397060000)
     (column=65787472615f696e666f, value=6e6f6e65, timestamp=1290554397060000)
     (column=726561736f6e, value=6e6f6e65, timestamp=1290554397060000)
     (column=7365636f6e64735f746f5f6e657874, value=373530, timestamp=1290554397060000)
     (column=73657269616c, value=393135353032353731, timestamp=1290554397060000)
     (column=737461747573, value=5550, timestamp=1290554397060000)
     (column=74797065, value=486561727462656174, timestamp=1290554397060000))
=> (super_column=7c959f00-f757-11df-7c95-9f00f75711df,
     (column=64617465, value=323031302d31312d32332032333a31343a30332e303030, timestamp=1290554096881000)
     (column=65787472615f696e666f, value=6e6f6e65, timestamp=1290554096881000)
     (column=726561736f6e, value=6e6f6e65, timestamp=1290554096881000)
     (column=7365636f6e64735f746f5f6e657874, value=373530, timestamp=1290554096881000)
     (column=73657269616c, value=393135353032353731, timestamp=1290554096881000)
     (column=737461747573, value=5550, timestamp=1290554096881000)
     (column=74797065, value=486561727462656174, timestamp=1290554096881000))
=> (super_column=c9be6330-f756-11df-c9be-6330f75611df,
     (column=64617465, value=323031302d31312d32332032333a30393a30332e303030, timestamp=1290553796836000)
     (column=65787472615f696e666f, value=6e6f6e65, timestamp=1290553796836000)
     (column=726561736f6e, value=6e6f6e65, timestamp=1290553796836000)
     (column=7365636f6e64735f746f5f6e657874, value=373530, timestamp=1290553796836000)
     (column=73657269616c, value=393135353032353731, timestamp=1290553796836000)
     (column=737461747573, value=5550, timestamp=1290553796836000)
     (column=74797065, value=486561727462656174, timestamp=1290553796836000))
=> (super_column=17108150-f756-11df-1710-8150f75611df,
     (column=64617465, value=323031302d31312d32332032333a30343a30332e303030, timestamp=1290553497067000)
     (column=65787472615f696e666f, value=6e6f6e65, timestamp=1290553497067000)
     (column=726561736f6e, value=6e6f6e65, timestamp=1290553497067000)
     (column=7365636f6e64735f746f5f6e657874, value=373530, timestamp=1290553497067000)
     (column=73657269616c, value=393135353032353731, timestamp=1290553497067000)
     (column=737461747573, value=5550, timestamp=1290553497067000)
     (column=74797065, value=486561727462656174, timestamp=1290553497067000))
=> (super_column=641da730-f755-11df-641d-a730f75511df,
     (column=64617465, value=323031302d31312d32332032323a35393a30332e303030, timestamp=1290553196836000)
     (column=65787472615f696e666f, value=6e6f6e65, timestamp=1290553196836000)
     (column=726561736f6e, value=6e6f6e65, timestamp=1290553196836000)
     (column=7365636f6e64735f746f5f6e657874, value=373530, timestamp=1290553196836000)
     (column=73657269616c, value=393135353032353731, timestamp=1290553196836000)
     (column=737461747573, value=5550, timestamp=1290553196836000)
     (column=74797065, value=486561727462656174, timestamp=1290553196836000))
=> (super_column=4bce9420-f753-11df-4bce-9420f75311df,
     (column=64617465, value=323031302d31312d32332032323a34343a30332e303030, timestamp=1290552297060000)
     (column=65787472615f696e666f, value=6e6f6e65, timestamp=1290552297060000)
     (column=726561736f6e, value=6e6f6e65, timestamp=1290552297060000)
     (column=7365636f6e64735f746f5f6e657874, value=373530, timestamp=1290552297060000)
     (column=73657269616c, value=393135353032353731, timestamp=1290552297060000)
     (column=737461747573, value=5550, timestamp=1290552297060000)
     (column=74797065, value=486561727462656174, timestamp=1290552297060000))

On Wed, Dec 1, 2010 at 2:25 PM, Aaron Morton <aaron@thelastpickle.com> wrote:
The Partitioner applies to the row keys, not the columns. Their order is determined by the
compare_with and compare_subcolumns_with CF settings 

So where you say "get the last 25 inserts for a key" I'm translating that into "get the most
recent 25 super columns for a row, where the super column names are UUID's and the CF definition
has compare_with:  TimeUUIDType" 

You can send a get_slice where the SliceRange has count=25 and reversed=True. If you know
the 25th col name you can use it as the start param, and AFAIK the operation would go faster.
Not sure how this translates into calls against Pelops. 

This assumes you are using time / v1 UUID's that have an increasing order. 

Hope that helps. 

Aaron



On 02 Dec, 2010,at 09:19 AM, Frank LoVecchio <frank@isidorey.com> wrote:

Is it possible to perform paginated queries using Random Partitioner in 0.7 with Super Column
Families whose Super Columns are UUID's?  I don't believe it is, based on this article: http://ria101.wordpress.com/2010/02/22/cassandra-randompartitioner-vs-orderpreservingpartitioner,
and my attempts with Pelops.

Let's say I get the last 25 inserts for a key.  I now know the 25th Super Column UUID, and
I want to start from there and get the next 25 inserts.  Do I have to change over to Order
Preserving Partitioner?  I'd like to avoid this at all costs.

Thanks,

Frank


Mime
  • Unnamed multipart/alternative (inline, None, 0 bytes)
    • Unnamed multipart/related (inline, None, 0 bytes)
View raw message