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Date: Mon, 25 Jan 2016 15:44:08 +0100
Message-ID: <CAKJqnrGq41ZvGByfH53n1=wJtPZghk+zyNOwZX8RXbJWcr=Xog@mail.gmail.com>
From: Marco Falke <falke.marco@gmail.com>
Cc: bitcoin-dev@lists.linuxfoundation.org
Content-Type: text/plain; charset=UTF-8
Subject: Re: [bitcoin-dev] Bitcoin Core 0.12.0 release candidate 1 available
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All of this is already implemented in the bitcoind and bitcoin gui.

The theoretic minimum for the prune target would be 0 (just the header
of the current best block) as Bitcoin Core already stores the
chainstate (about 2 GiB) regardless of what you set for -prune=<N>.

In practice, the minimum is 510, so reorgs and small rescans (may not
be implemented in 0.12) are still possible.

The clients won't let you set it below that target:
"Prune configured below the minimum of 550 MiB. Please use a higher number."

Also, keep in mind Bitcoin Core comes with a help message explaining
-prune and other command line options

--Marco

2016-01-25 13:27 GMT+01:00 xor--- via bitcoin-dev
<bitcoin-dev@lists.linuxfoundation.org>:
> On Monday, January 25, 2016 01:03:17 PM Wladimir J. van der Laan wrote:
>> > If yes, I would highly recommend advertising it in the new release notes -
>> > as said, the disk space reduction is a big deal.
>>
>> Good idea, has been added by Marco Falke in commit fa31133,
>
> Thanks. The RC2 changelog now says:
>
>> To enable block pruning set prune=<N> on the command line or in
>> bitcoin.conf, where N is the number of MiB to allot for raw block & undo
>> data.
>
> From having read the Bitcoin whitepaper quite a few months ago ago, I have the
> very very basic understanding that pruning is meant to:
> - delete old transaction data which merely "moves coins around"
> - instead only store the "origin" (= block where coins were mined) and
> "current location" of the coins, i.e. the unspent transactions. Notably, I
> understood it as "this is as secure as storing everything, since we know where
> the coins were created, and where they are".
>
> So from that point of view, I would assume that there is a "natural" amount of
> megabytes which a fully pruned blockchain consists of: It would be defined by
> the final amount of unspent coins.
> I thereby am confused why it is possible to configure a number of megabytes
> "to allot for raw block & undo data". I would rather expect pruning just to be
> a boolean on/off flag, and the number of megabytes to be an automatically
> computed result from the natural size of the dataset.
> And especially, I fear that I could set N too low, and as a result, it would
> delete "too much". I mean could this result in even security relevant
> transaction data being deleted?
>
> Thus, it would be nice if you could yet once more edit the release notes to:
> - explain why a N must be given
> - what a "safe" value of N is. I.e. how large must N be at least to not delete
> security-relevant stuff?
> - maybe mention if there is a "auto" setting for N to ensure that it choses a
> safe value on its own?
>
> Sorry if my descriptions are from a layman's point of view. I intentionally
> did *not* re-read the Bitcoin whitepaper to have a better understanding:
> I think having a layman's understanding is a good usability test for such
> stuff.
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