Mailing-List: contact dev-help@cassandra.apache.org; run by ezmlm
Precedence: bulk
Reply-To: dev@cassandra.apache.org
Received-SPF: pass (nike.apache.org: domain of sahmed1020@gmail.com designates
 209.85.220.216 as permitted sender)
DomainKey-Signature: a=rsa-sha1; c=nofws;
        d=gmail.com; s=gamma;
        h=mime-version:date:message-id:subject:from:to:content-type;
        b=sRStkaEvBj+pwGH8LvZe5hgNsmoCaklzZedRZzJvP7mTdwQb0MRwBLMGWIs9m7LFEu
         H0c2m+YxlFdWZfD05izTIvsJcRO3XujNoU+Tu3WkPeKKUoca63T6KuwvnrDdabZgH5Ia
         adqlmjEXdWW0F5IJ9MS3zd33tYS+Naxksc798=
MIME-Version: 1.0
Date: Wed, 7 Apr 2010 16:27:25 -0400
Message-ID: <o2o5feb12801004071327i147a4fa5vbbd23fc1792a83f6@mail.gmail.com>
Subject: boonfilters
From: S Ahmed <sahmed1020@gmail.com>
To: dev@cassandra.apache.org
Content-Type: multipart/alternative; boundary=000e0cdfd990eca0310483ab6306

--000e0cdfd990eca0310483ab6306
Content-Type: text/plain; charset=ISO-8859-1

Just reading up on boonfilters, few questions.

Basically boonfilters let give you a true/false if a particular key exists,
and they *may* give you a false positive i.e. they key exists but never a
false negative i.e. the key doesn't exist.

The core of boonfilters is its hashing mechanism that marks the in-memory
matrix/map if the key exists.

1. Is the only place boonfilters are used in Cassandra is when you want to
see if a particular key exists in a particular node?

2. Are boonfilters a fixed size, or they adjust as to the # of keys?  any
example size?

3. Boonfilters don't give false negatives:
    So you hit a node, and perform a lookup in the boonfilter for a key.  It
says "yes", but when you do a lookup the object returned is null, so then
you flag that this node needs this particular key during replication.


Have I grasp this concept?

Really loving this project, learning allot from the code.  It would be great
if someone could do a walkthrough of common functionality in a detailed way
:)

--000e0cdfd990eca0310483ab6306--