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From: Michael Gronager <gronager@ceptacle.com>
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To: Mike Hearn <mike@plan99.net>
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Cc: Bitcoin Dev <bitcoin-development@lists.sourceforge.net>
Subject: Re: [Bitcoin-development] Warning: many 0.7 nodes break on large
	number of tx/block; fork risk
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Well a reversed upgrade is an upgrade that went wrong ;)

Anyway, the incident makes it even more important for people to upgrade, =
well except, perhaps, for miners...

Forks are caused by rejection criteria, hence:=20
1. If you introduce new rejection criteria in an upgrade miners should =
upgrade _first_.
2. If you loosen some rejection criteria miners should upgrade _last_.
3. If you keep the same criteria assume 2.

/M

On 12/03/2013, at 13:11, Mike Hearn <mike@plan99.net> wrote:

> I'm not even sure I'd say the upgrade "went wrong". The problem if
> anything is the upgrade didn't happen fast enough. If we had run out
> of block space a few months from now, or if miners/merchants/exchanges
> had upgraded faster, it'd have made more sense to just roll forward
> and tolerate the loss of the older clients.
>=20
> This really reinforces the importance of keeping nodes up to date.
>=20
> On Tue, Mar 12, 2013 at 12:44 PM, 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.
>>=20
>> 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.
>>=20
>> 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...
>>=20
>>> 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:
>>>=20
>>> 1. if they gets to old >24hr
>>> 2. if the client is running out of space, then the oldest should =
probably be pruned
>>>=20
>>> 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).
>>=20
>> Right now, mempools are relatively small in memory usage, but with =
small block sizes,
>> it indeed risks going up. In 0.8, conflicting (=3Ddouble 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.
>>=20
>> 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.
>>=20
>> However, the presence of this bug, and the fact that a full solution =
is available (0.8),
>> probably helps achieving consensus fixing it (=3Da hardfork) is =
needed, and we should take
>> advantage of that. But please, let's not rush things...
>>=20
>> --
>> Piter
>=20
> =
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Forrester =20
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