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From Jonathan Ellis <jbel...@gmail.com>
Subject Re: bitmap slices
Date Mon, 01 Feb 2010 16:41:28 GMT
I don't think this is very useful for column names.  I could see it
being useful for values but if we're going to add predicate queries
then I'd rather do something more general.

2010/2/1 Ted Zlatanov <tzz@lifelogs.com>:
> On Mon, 1 Feb 2010 09:42:16 -0600 Jonathan Ellis <jbellis@gmail.com> wrote:
>
> JE> 2010/2/1 Ted Zlatanov <tzz@lifelogs.com>:
>>> On Fri, 29 Jan 2010 15:07:01 -0600 Ted Zlatanov <tzz@lifelogs.com> wrote:
>>>
> TZ> On Fri, 29 Jan 2010 12:06:28 -0600 Jonathan Ellis <jbellis@gmail.com> wrote:
> JE> On Fri, Jan 29, 2010 at 9:09 AM, Mehar Chaitanya
> JE> <meharchaitanya@gmail.com> wrote:
>>>>>>   1. This would lead to enourmous amount of duplication of data,
in short
>>>>>>   if I now want to view the data from IS_PUBLISHED dimenstion then
my database
>>>>>>   size would scale up tremendously.
>>>
> JE> Yes.  But disk space is so cheap it's worth using a lot of it to make
> JE> other things fast.
>>>
> TZ> IIUC, Mehar would be duplicating the article data for every article tag.
>>>
> TZ> I searched the bug tracker and wiki and didn't find anything on the
> TZ> topic of tag storage and search, so I don't think Cassandra supports
> TZ> tags without data duplication.
>>>
> TZ> Would it be possible to implement an optional byte[] bitmap field in
> TZ> SliceRange?  If you can specify the bitmap as an optional field it would
> TZ> not break current clients.  Then the search can return only the subset
> TZ> of the range that matches the bitmap.  This would make sense for
> TZ> BytesType and LongType, at least.
>>>
>>> I looked at the source code and it seems that
>>> StorageProxy::getSliceRange() is the focal point for reads and bitmap
>>> matching should be implemented there.  The bitmap could be applied as a
>>> filter before the other SliceRange parameters, especially the max number
>>> of return results.  It may be worth the effort to send the bitmap down
>>> to the ReadCommand/ColumnFamily level to reduce the number of potential
>>> matches.
>>>
>>> If this is not feasible for technical reasons I'd like to know.
>>> Otherwise I'll put it on my TODO list and produce a proposal (unless
>>> someone more knowledgeable is interested, of course).
>
> JE> how would this be different then the byte[] column name you can
> JE> already match on?
>
> Given byte columns
>
> A 0110
> B 0111
> C 0101
>
> the bitmask approach would let you specify a bitmask of "0011" and get
> only B.  It's just an AND that looks for a non-zero value.  So you can
> say "0111" and get A, B, and C.  Or "0010" to get A and B.  "1000" gets
> nothing.
>
> Cassandra could support OR-ed multiples for better queries, so you could
> ask for (0001,0010) to get A, B, and C.
>
> Ted
>
>

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