cassandra-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From David Boxenhorn <da...@lookin2.com>
Subject Re: Re: Range search on keys not working?
Date Wed, 09 Jun 2010 11:29:32 GMT
To use start and finish parameters at all, you need to use OPP. Start and
finish parameters don't work if you don't use OPP, i.e. the result set won't
be:  start =< resultSet < finish

2010/6/9 Ben Browning <ben324@gmail.com>

> 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 <ywf2008@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 <david@lookin2.com>
> wrote:
> >> So why do the "start" and "finish" range parameters exist?
> >>
> >> On Wed, Jun 2, 2010 at 3:53 PM, Ben Browning <ben324@gmail.com> wrote:
> >>>
> >>> Martin,
> >>>
> >>> On Wed, Jun 2, 2010 at 8:34 AM, Dr. Martin Grabmüller
> >>> <Martin.Grabmueller@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:david@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.Grabmueller@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:david@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 <david@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 <tcurdt@vafer.org>
> >>> >>> wrote:
> >>> >>>>
> >>> >>>> Sounds like you are not using an order preserving partitioner?
> >>> >>>>
> >>> >>>> On Wed, Jun 2, 2010 at 13:48, David Boxenhorn <david@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
>

Mime
View raw message