From: Bob McElrath <bob_bitcoin@mcelrath•org>
To: bfd@cock•lu
Cc: bitcoin-dev@lists•linuxfoundation.org
Subject: Re: [bitcoin-dev] Committed bloom filters for improved wallet performance and SPV security
Date: Wed, 11 May 2016 20:06:48 +0000 [thread overview]
Message-ID: <20160511200648.GQ20063@mcelrath.org> (raw)
In-Reply-To: <71d822e413ac457a530e1c367811cc24@cock.lu>
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I like this idea, but let's run some numbers...
bfd--- via bitcoin-dev [bitcoin-dev@lists•linuxfoundation.org] wrote:
> A Bloom Filter Digest is deterministically created of every block
Bloom filters completely obfuscate the required size of the filter for a desired
false-positive rate. But, an optimal filter is linear in the number of elements
it contains for fixed false-positive rate, and logarithmic in the false-positive
rate. (This comment applies to a RLL encoded Bloom filter Greg mentioned, but
that's not the only way) That is for N elements and false positive rate
\epsilon:
filter size = - N \log_2 \epsilon
Given that the data that would be put into this particular filter is *already*
hashed, it makes more sense and is faster to use a Cuckoo[1] filter, choosing a
fixed false-positive rate, given expected wallet sizes. For Bloom filters,
multiply the above formula by 1.44.
To prevent light clients from downloading more blocks than necessary, the
false-positive rate should be roughly less than 1/(block height). If we take
the false positive rate to be 1e-6 for today's block height ~ 410000, this is
about 20 bits per element. So for todays block's, this is a 30kb filter, for a
3% increase in block size, if blocks commit to the filter. Thus the required
size of the filter commitment is roughly:
filter size = N \log_2 H
where H is the block height. If bitcoin had these filters from the beginning, a
light client today would have to download about 12MB of data in filters. My
personal SPV wallet is using 31MB currently. It's not clear this is a bandwidth
win, though it's definitely a win for computing load on full nodes.
[1] https://www.cs.cmu.edu/~dga/papers/cuckoo-conext2014.pdf
--
Cheers, Bob McElrath
"For every complex problem, there is a solution that is simple, neat, and wrong."
-- H. L. Mencken
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next prev parent reply other threads:[~2016-05-11 20:17 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-09 8:26 bfd
2016-05-09 8:57 ` Gregory Maxwell
2016-05-11 20:06 ` Bob McElrath [this message]
2016-05-11 20:29 ` Bob McElrath
2016-07-28 21:07 ` Leo Wandersleb
2017-01-06 22:07 ` Erik Aronesty
2017-01-03 20:24 ` bfd
[not found] ` <77b6dd25-0603-a0bd-6a9e-38098e5cb19d@jonasschnelli.ch>
2017-01-03 20:18 ` bfd
2017-01-03 22:18 ` Aaron Voisine
2017-01-03 22:28 ` bfd
2017-01-03 23:06 ` adiabat
2017-01-03 23:46 ` Aaron Voisine
2017-01-04 0:10 ` bfd
2017-01-04 0:36 ` Aaron Voisine
2017-01-04 6:06 ` Eric Voskuil
2017-01-04 16:13 ` Leo Wandersleb
2017-01-04 7:47 ` Jonas Schnelli
2017-01-04 8:56 ` Aaron Voisine
2017-01-04 10:13 ` Jorge Timón
2017-01-04 11:00 ` Adam Back
2017-01-06 2:15 ` bfd
2017-01-06 7:07 ` Aaron Voisine
2017-01-05 7:06 ` Chris Priest
2017-01-05 7:45 ` Eric Voskuil
2017-01-05 14:48 ` Christian Decker
2017-01-06 20:15 ` Chris Priest
2017-01-06 21:35 ` James MacWhyte
2017-01-06 21:50 ` Eric Voskuil
2017-01-06 2:04 ` bfd
2017-03-15 22:36 ` Tom Harding
2017-03-16 0:25 ` bfd
2017-03-16 15:05 ` Tom Harding
2017-02-17 0:28 ` Chris Belcher
2017-04-01 23:49 ` bfd
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