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From Ted Zlatanov <...@lifelogs.com>
Subject Re: bitmap slices
Date Thu, 04 Feb 2010 15:14:04 GMT
On Wed, 3 Feb 2010 17:06:32 -0600 Jonathan Ellis <jbellis@gmail.com> wrote: 

JE> It seems to me that the bitmask is only really useful for the
JE> SliceRange predicate.  Doing a predicate of "fetch these column names,
JE> but only if they match this mask" seems strange.

You're right, I put it at the wrong level.

JE> The mask check needs to be done in the Slice Filter, not SP.

Sorry, I don't know what you mean.  Are you referring to
o.a.c.db.filter.SliceQueryFilter?  So I'd just add an extra parameter to
the constructor and change the matching logic?  Or should I derive a new
class for backwards compatibility?

I also realized I should have just used a BitSet to do the matching
logic for me.

JE> Is this actually powerful enough to solve a real problem for you?

Yes!  OR+AND are exactly what I need.

One specific situation: a supercolumn holds byte[] keys representing
network addresses (IPv4, IPv6, and Infiniband).  I want to do efficient
queries across them by various netmasks; the netmasks are not trivial
and need the OR+AND structure.  Right now I do it all on the client
side.  I can't break things down by key or by supercolumn further
because I already use the supercolumn as a time (Long) index and the key
represents the specific colo.

I have other examples but they'd require too much explanation of my
company's infrastructure.

I've seen at least 4 real examples in the last 2 weeks on the dev and
user Cassandra mailing lists where some kind of data tagging could be
useful instead of just the range query.  The original article example
that started this thread, for instance, could have used that approach to
tag the articles and reduce the need for data duplication.

Thanks
Ted


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