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From Todd Nine <t...@spidertracks.com>
Subject Re: Status of LT LTE without EQ op for 0.7 release
Date Wed, 13 Oct 2010 18:45:50 GMT
Hi Tyler,
  That was the original scheme I was describing in the original email.
Unfortunately, I can have more that one value per column, so I actually
have to use super columns.  This way I can write more that one row key
for any given indexed value.  I'm concerned that this may not scale well
(at least on version 0.6).  However after looking at the limitations
page.

http://wiki.apache.org/cassandra/CassandraLimitations

It appears that the "row must fit in memory" has been removed.  I'll
move back to this scheme for my querying.

todd 
SENIOR SOFTWARE ENGINEER

todd nine| spidertracks ltd |  117a the square 
po box 5203 | palmerston north 4441 | new zealand 
P: +64 6 353 3395 | M: +64 210 255 8576  
E: todd@spidertracks.co.nz W: www.spidertracks.com 





On Tue, 2010-10-12 at 23:01 -0500, Tyler Hobbs wrote:

> I'm not completely sure I follow your scheme, but it's fairly to
> support
> GT, LT, etc with your own index.
> 
> Use a row for your index where the columns names are the data values
> you want to index.  If you set the comparator type (in your example,
> this
> would be LongType), you can perform a LT or GT query just by getting a
> slice of the index columns.  Store the original data row keys as the
> column
> values, and you're there.
> 
> - Tyler
> 
> 
> On Tue, Oct 12, 2010 at 9:33 PM, Todd Nine <todd@spidertracks.com>
> wrote:
> 
>         Thanks Johnathan,
>         
>         A follow up question.  Will it be possible to migrate existing
>         indexes
>         in a future release as part of the upgrade path to support LT
>         and LTE
>         ops without equal?   In the meantime in my Datanucleus Plugin
>         I was
>         thinking I could do something like the following.  It's not
>         efficient
>         for space, but it will work and should hopefully be relatively
>         efficient
>         for querying.
>         
>         
>         LT and LTE ops can be though of as the distance from the MAX
>         value of
>         any given data type.  For instance, if I had a data
>         type :"ubershort",
>         which goes from -200 to 200, I could say that an expression of
>         <= 0 is
>         really >= (distance) 200 from the maximum.  I could use this
>         equation to
>         calculate the "distance" to persist a distance value in a
>         column named
>         "<colName>_reverse". Which would effectively give me a reverse
>         index.
>         
>         
>         Then the value would simply be
>         
>         storedValue = MAXVALUE-userVal.
>         
>         >From there, whenever the user issues a < <= query, I would
>         simply
>         translate the value via the above equation and < becomes > and
>         <=
>         becomes >=.  Aside from the space issue of storage, do you see
>         any other
>         problems with this approach for a 0.7 compatible version of my
>         plugin?
>         
>         Thanks,
>         Todd
>         
>         
>         
>         
>         
>         
>         
>         On Wed, 2010-10-13 at 14:00 +1300, Todd Nine wrote:
>         
>         > Fair enough!
>         >
>         >
>         > Thanks Jonathan.
>         >
>         >
>         > todd
>         > SENIOR SOFTWARE ENGINEER
>         >
>         > todd nine| spidertracks ltd |  117a the square
>         > po box 5203 | palmerston north 4441 | new zealand
>         > P: +64 6 353 3395 | M: +64 210 255 8576
>         > E: todd@spidertracks.co.nz W: www.spidertracks.com
>         >
>         >
>         >
>         >
>         >
>         >
>         >
>         > On Tue, 2010-10-12 at 18:47 -0500, Jonathan Ellis wrote:
>         >
>         > > On Tue, Oct 12, 2010 at 6:34 PM, Todd Nine
>         <todd@spidertracks.com> wrote:
>         > > > Currently there is only indexing for LT and LTE
>         expression when an EQ
>         > > > operator is present.  Will it be possible to use the LT
>         and LTE ops
>         > > > without an EQ by the 0.7.0 release?
>         > >
>         > > No.
>         > >
>         > > >  If not, which of the following
>         > > > would be more efficient?
>         > > >
>         > > > 1. Creating a dummy column of 1 byte that is indexed.
>         > >
>         > > This is basically the same as doing a full range scan,
>         only less efficient.
>         > >
>         > > > 2. Use my previous indexing scheme of 2 Super CF for
>         longs and strings
>         > > > to get my < <= operations.  Where I use the following
>         scheme.
>         > >
>         > > I'm not sure I follow but if it's better than doing a full
>         range scan
>         > > then it is better than 1. :)
>         > >
>         
> 
> 

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