From: Kaz Wesley <keziahw@gmail•com>
To: Gregory Maxwell <gmaxwell@gmail•com>
Cc: Bitcoin Dev <bitcoin-development@lists•sourceforge.net>
Subject: Re: [Bitcoin-development] Squashing redundant tx data in blocks on the wire
Date: Thu, 31 Jul 2014 15:27:59 -0700 [thread overview]
Message-ID: <CA+iPb=FV1_0SCzcqCz+2eeQW6L18c2O2aKW4zusgNKBYirqHcA@mail.gmail.com> (raw)
In-Reply-To: <CAAS2fgSObqk=rD1vtV6LZzxUuyQMh+nwGuatOq1hUaQz2od0sg@mail.gmail.com>
> the FEC still lets you fill in the missing transactions without knowing in advance all that will be missing.
I don't see why we need to solve that problem, since the protocol
already involves exchanging the information necessary to determine
(with some false positives) what a peer is missing, and needs to
continue doing so regardless of how blocks are transmitted.
Set reconciliation does have the benefit of eliminating a subset of
those false positives and offering a finer-grained mechanism for
defining what a node can choose to forget from its mempool than
remember-last-N, but if we implement it for block transmission I don't
see why we wouldn't also use it to synchronize mempool txes, and if
mempools are synchronized we don't actually need to do it as part of
block-transmission to get those benefits.
As far as I can tell, channel memory sparseblocks achieve most of the
possible bandwidth savings, and when FEC-based mempool synchronization
is implemented its benefits can be applied to the sparseblocks by
resetting the channel memory to the mutual mempool state each time
mempool differences are exchanged. Am I missing a benefit to doing FEC
at block forwarding time that can't be realized by FEC-based mempool
synchronization, implemented separately from channel-memory based
index-coding?
On Thu, Jul 31, 2014 at 2:51 PM, Gregory Maxwell <gmaxwell@gmail•com> wrote:
> On Thu, Jul 31, 2014 at 2:41 PM, Kaz Wesley <keziahw@gmail•com> wrote:
>>> the need to have transmitted the transaction list [..] first
>>
>> 32 bits per transaction is at least double the communication overhead
>> of the simple approach, and only offers a bound on the probability of
>> needing a round trip.
>
> "(e.g. from a reconciliation step first)" the list can be communicated
> in the space roughly equal to the size of the difference in sets plus
> coding the permutation from the permissible orderings. If you did
> have some "simple approach" that guaranteed that some transactions
> would be present, then you could code those with indexes... the FEC
> still lets you fill in the missing transactions without knowing in
> advance all that will be missing. (Also, the suggestion on the
> network block coding page of using part of a cryptographic permutation
> as the key means that for unknown transactions the transmission of the
> new unknown keys is always goodput— doesn't add overhead)
>
> It's "only a bound" but you can pick whatever bound you want,
> including— if you send data equal to the missing amount, then it'll be
> always successful, but no bandwidth savings. Though if the transport
> is unordered (e.g. UDP or non-blocking SCTP) even sending 100% of the
> missing amount can save time by eliminating a round trip that might
> otherwise be needed for a retransmission.
next prev parent reply other threads:[~2014-07-31 22:28 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-07-17 21:35 Kaz Wesley
2014-07-17 22:46 ` Gavin Andresen
2014-07-17 23:26 ` Kaz Wesley
2014-07-18 13:53 ` Jeff Garzik
2014-07-18 14:53 ` Gavin Andresen
2014-07-18 15:06 ` Jeff Garzik
2014-07-18 17:39 ` Kaz Wesley
2014-07-18 17:48 ` Jeff Garzik
2014-07-18 17:53 ` Kaz Wesley
2014-07-18 19:51 ` Kaz Wesley
2014-07-18 19:55 ` Jeff Garzik
2014-07-19 0:54 ` Emin Gün Sirer
2014-07-19 1:25 ` Gregory Maxwell
2014-07-19 3:06 ` Emin Gün Sirer
2014-07-19 6:48 ` Gregory Maxwell
2014-07-19 8:06 ` Wladimir
2014-07-17 23:34 ` Gregory Maxwell
[not found] ` <CABsx9T2PSa3MpfMMDCb8ACVF5vDOZOFLEK9zfP9PakgHA4U16w@mail.gmail.com>
[not found] ` <CAPkFh0vKFnKRE-sd-Z9t1zB73VLPsiaQ3o=OYgBqqtUE4_rTaw@mail.gmail.com>
2014-07-31 20:47 ` Kaz Wesley
2014-07-31 21:29 ` Gregory Maxwell
2014-07-31 21:41 ` Kaz Wesley
2014-07-31 21:51 ` Gregory Maxwell
2014-07-31 22:27 ` Kaz Wesley [this message]
2014-07-31 23:18 ` Gregory Maxwell
2014-08-01 1:00 ` Kaz Wesley
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