OPP stands for Order-Preserving Partitioner. For more information on partitioners, look here:
http://wiki.apache.org/cassandra/StorageConfiguration#Partitioner To do key range slices that use both start and finish parameters and retrieve keys in-order, you need to use an ordered partitioner - either the built-in OPP or your own custom one. Ben On Tue, Jun 8, 2010 at 10:26 PM, sina <ywf2...@sina.com> wrote: > what's the mean of opp? And How can i make the "start" and "finish" useful > and make sense? > > > 2010-06-09 > ________________________________ > 9527 > ________________________________ > 发件人： Ben Browning > 发送时间： 2010-06-02 21:08:57 > 收件人： user > 抄送： > 主题： Re: Range search on keys not working? > They exist because when using OPP they are useful and make sense. > On Wed, Jun 2, 2010 at 8:59 AM, David Boxenhorn <da...@lookin2.com> wrote: >> So why do the "start" and "finish" range parameters exist? >> >> On Wed, Jun 2, 2010 at 3:53 PM, Ben Browning <ben...@gmail.com> wrote: >>> >>> Martin, >>> >>> On Wed, Jun 2, 2010 at 8:34 AM, Dr. Martin Grabmüller >>> <martin.grabmuel...@eleven.de> wrote: >>> > I think you can specify an end key, but it should be a key which does >>> > exist >>> > in your column family. >>> >>> >>> Logically, it doesn't make sense to ever specify an end key with >>> random partitioner. If you specified a start key of "aaa" and and end >>> key of "aac" you might get back as results "aaa", "zfc", "hik", etc. >>> And, even if you have a key of "aab" it might not show up. Key ranges >>> only make sense with order-preserving partitioner. The only time to >>> ever use a key range with random partitioner is when you want to >>> iterate over all keys in the CF. >>> >>> Ben >>> >>> >>> > But maybe I'm off the track here and someone else here knows more about >>> > this >>> > key range stuff. >>> > >>> > Martin >>> > >>> > ________________________________ >>> > From: David Boxenhorn [mailto:da...@lookin2.com] >>> > Sent: Wednesday, June 02, 2010 2:30 PM >>> > To: user@cassandra.apache.org >>> > Subject: Re: Range search on keys not working? >>> > >>> > In other words, I should check the values as I iterate, and stop >>> > iterating >>> > when I get out of range? >>> > >>> > I'll try that! >>> > >>> > On Wed, Jun 2, 2010 at 3:15 PM, Dr. Martin Grabmüller >>> > <martin.grabmuel...@eleven.de> wrote: >>> >> >>> >> When not using OOP, you should not use something like 'CATEGORY/' as >>> >> the >>> >> end key. >>> >> Use the empty string as the end key and limit the number of returned >>> >> keys, >>> >> as you did with >>> >> the 'max' value. >>> >> >>> >> If I understand correctly, the end key is used to generate an end token >>> >> by >>> >> hashing it, and >>> >> there is not the same correspondence between 'CATEGORY' and 'CATEGORY/' >>> >> as >>> >> for >>> >> hash('CATEGORY') and hash('CATEGORY/'). >>> >> >>> >> At least, this was the explanation I gave myself when I had the same >>> >> problem. >>> >> >>> >> The solution is to iterate through the keys by always using the last >>> >> key >>> >> returned as the >>> >> start key for the next call to get_range_slices, and the to drop the >>> >> first >>> >> element from >>> >> the result. >>> >> >>> >> HTH, >>> >> Martin >>> >> >>> >> ________________________________ >>> >> From: David Boxenhorn [mailto:da...@lookin2.com] >>> >> Sent: Wednesday, June 02, 2010 2:01 PM >>> >> To: user@cassandra.apache.org >>> >> Subject: Re: Range search on keys not working? >>> >> >>> >> The previous thread where we discussed this is called, "key is sorted?" >>> >> >>> >> >>> >> On Wed, Jun 2, 2010 at 2:56 PM, David Boxenhorn <da...@lookin2.com> >>> >> wrote: >>> >>> >>> >>> I'm not using OPP. But I was assured on earlier threads (I asked >>> >>> several >>> >>> times to be sure) that it would work as stated below: the results >>> >>> would not >>> >>> be ordered, but they would be correct. >>> >>> >>> >>> On Wed, Jun 2, 2010 at 2:51 PM, Torsten Curdt <tcu...@vafer.org> >>> >>> wrote: >>> >>>> >>> >>>> Sounds like you are not using an order preserving partitioner? >>> >>>> >>> >>>> On Wed, Jun 2, 2010 at 13:48, David Boxenhorn <da...@lookin2.com> >>> >>>> wrote: >>> >>>> > Range search on keys is not working for me. I was assured in >>> >>>> > earlier >>> >>>> > threads >>> >>>> > that range search would work, but the results would not be ordered. >>> >>>> > >>> >>>> > I'm trying to get all the rows that start with "CATEGORY." >>> >>>> > >>> >>>> > I'm doing: >>> >>>> > >>> >>>> > String start = "CATEGORY."; >>> >>>> > . >>> >>>> > . >>> >>>> > . >>> >>>> > keyspace.getSuperRangeSlice(columnParent, slicePredicate, start, >>> >>>> > "CATEGORY/", max) >>> >>>> > . >>> >>>> > . >>> >>>> > . >>> >>>> > >>> >>>> > in a loop, setting start to the last key each time - but I'm >>> >>>> > getting >>> >>>> > rows >>> >>>> > that don't start with "CATEGORY."!! >>> >>>> > >>> >>>> > How do I get all rows that start with "CATEGORY."? >>> >>> >>> >> >>> > >>> > >> >> > __________ Information from ESET NOD32 Antivirus, version of virus signature > database 5164 (20100601) __________ > The message was checked by ESET NOD32 Antivirus. > http://www.eset.com
