Re: [Bitcoin-development] Warning: many 0.7 nodes break on large number of tx/block; fork risk

["\ Jorge Timón" <jtimonmv@gmail.com>]

A related question...some people mentioned yesterday on #bitcoin-dev
that 0.5 appeared to be compatible with 0.8.
Was that only for the "fatal block" and would have forked 0.8 later
too or is it something else?
I'm having a hard time understanding this 0.5 thing, if someone can
bring some light to it I would appreciate it.

Thanks in advance

On 3/12/13, Pieter Wuille <pieter.wuille@gmail.com> wrote:
> On Tue, Mar 12, 2013 at 11:13:09AM +0100, Michael Gronager wrote:
>> Yes, 0.7 (yes 0.7!) was not sufficiently tested it had an undocumented and
>> unknown criteria for block rejection, hence the upgrade went wrong.
>
> We're using "0.7" as a short moniker for all clients, but this was a
> limitation that all
> BDB-based bitcoins ever had. The bug is simply a limit in the number of lock
> objects
> that was reached.
>
> It's ironic that 0.8 was supposed to solve all problems we had due to BDB
> (except the
> wallet...), but now it seems it's still coming back to haunt us. I really
> hated telling
> miners to go back to 0.7, given all efforts to make 0.8 signficantly more
> tolerable...
>
>> More space in the block is needed indeed, but the real problem you are
>> describing is actually not missing space in the block, but proper handling
>> of mem-pool transactions. They should be pruned on two criteria:
>>
>> 1. if they gets to old >24hr
>> 2. if the client is running out of space, then the oldest should probably
>> be pruned
>>
>> clients are anyway keeping, and re-relaying, their own transactions and
>> hence it would mean only little, and only little for clients. Dropping
>> free / old transaction is a much a better behavior than dying... Even a
>> scheme where the client dropped all or random mempool txes would be a
>> tolerable way of handling things (dropping all is similar to a restart,
>> except for no user intervention).
>
> Right now, mempools are relatively small in memory usage, but with small
> block sizes,
> it indeed risks going up. In 0.8, conflicting (=double spending)
> transactions in the
> chain cause clearing the mempool of conflicts, so at least the mempool is
> bounded by
> the size of the UTXO subset being spent. Dropping transactions from the
> memory pool
> when they run out of space seems a correct solution. I'm less convinced
> about a
> deterministic time-based rule, as that creates a double spending incentive
> at that
> time, and a counter incentive to spam the network with your
> risking-to-be-cleared
> transaction as well.
>
> Regarding the block space, we've seen the pct% of one single block chain
> space consumer
> grow simultaneously with the introduction of larger blocks, so I'm not
> actually convinced
> there is right now a big need for larger blocks (note: right now). The
> competition for
> block chain space is mostly an issue for client software which doesn't deal
> correctly
> with non-confirming transactions, and misleading users. It's mostly a
> usability problem
> now, but increasing block sizes isn't guaranteed to fix that; it may just
> make more
> space for spam.
>
> However, the presence of this bug, and the fact that a full solution is
> available (0.8),
> probably helps achieving consensus fixing it (=a hardfork) is needed, and we
> should take
> advantage of that. But please, let's not rush things...
>
> --
> Piter
>
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-- 
Jorge Timón

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