[Bitcoin-development] Timed testing

[Bitcoin-development] Timed testing

[Jorge Timón]

I'm implementing a new testing mode that produces blocks
periodically. You can get what I have so far here:

https://github.com/jtimon/bitcoin/tree/timed

It depends on pull request #3824 with some improvements on
CChainParams, but after that the changes required to add this new
mode are very small:

https://github.com/jtimon/bitcoin/commit/445321928a143cb9a6f56777cbb7479dd32c3bcd

I guess I need a new genesis block, different magic numbers, etc. So
this is definitely not ready.
You can run it like this:

bitcoind -timedtest -gen=1 blocktime=2000

blocktime defaults to 1000 milliseconds for timedtest mode and 0 for
the rest of the modes.

What could this testing mode be useful for?

Basically, simulations.
For example, you could run several nodes implementing different mining
policies. Let's say I want to mine 50% of the blocks with standard policy,
25% with policy A and 25% with policy B. I can run 1 one for each of
one with block times 2000, 1000 and 1000 respectively.

Maybe I want to detect performance bottlenecks by stressing this mode
with as many transaction as can be processed, maybe removing the
block size limits in the simulations.

But this still doesn't serve for hardfork or double-spend attacks
simulations without calculating any pow, which would be another
interesting feature for a new testing mode.
I would like to implement the new mode following as the concept of
private chains described in freimarkets:

http://freico.in/docs/freimarkets.pdf
https://github.com/jtimon/freimarkets/blob/master/doc/freimarkets_specs.org#private-ledgers
https://github.com/jtimon/freimarkets/blob/master/doc/freimarkets_specs.org#off-chain-transactions

I know this could be considered a "non-bitcoinish" application and
therefore be controversial as discussed in PR 3824, so I want to keep
the conversation focused on testing use cases useful to bitcoin itself
only: additional changes can be implemented elsewhere.
One way I think you could support chain races simulations by using a
private mode could be the following:

1) The private mode works like the timed mode in how often it
   produces blocks.

2) In private mode you replace the pow-related fields with a
   blockPubkeyScript and a lastBlockSigScript fields. In the genesis
   block, lastBlockSigScript is empty and the initial
   blockPubkeyScript can be an optional parameter like blocktime. You
   can set any valid script, probably p2sh, maybe with multisig to
   allow different nodes to sign.

3) In this context, longer chains mean "more work". Another way to
   see it is that all blocks just contain work==1 in them.

So let's say we want to simulate an attack using 50% standard and 50%
attacker blocks. You set up the private mode script to be a 1 of 2
multisig and make each node sign always with the same private key
(maybe an additional parameter).
You make the attacker reject any blocks from height X that he hasn't
signed himself to get the result you wanted: the standard node will
produce blocks on top of the longest chain while the attacker will
only hash on top of his own blocks.

So my question to the community is, how invasive is this to bitcoin's
source code?
In my opinion, done properly could actually result (apart from getting
the new features) in more readable code, not less, since you will
probably need to make sure proof of work functionality is properly
encapsulated during the implementation process (see PR 3839 for a first
step on that direction).
But, should I push a private mode to the core or just the timed one
and implement the private mode elsewhere?

Of course other comments on the parameters, defaults or any other
design or implementation details are also welcomed.

-- 
Jorge Timón

http://freico.in/

Re: [Bitcoin-development] Timed testing

[Gavin Andresen]

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How is this different from just running in -regtest mode and asking the
nodes to generate a block after 1 or 2 seconds?

-- 
--
Gavin Andresen

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Re: [Bitcoin-development] Timed testing

[Jorge Timón]

On 4/17/14, Gavin Andresen <gavinandresen@gmail.com> wrote:
> How is this different from just running in -regtest mode and asking the
> nodes to generate a block after 1 or 2 seconds?

There's no difference, the -timedtest mode does exactly that. But
automatically instead of having to manually ask for a new block every
second.
I assume your position is that the difference is too small to justify
a new mode, or that you just don't see any value in it.

The -private mode, on the other hand, would allow you to simulate
proof of work attacks as described in the previous post, but maybe
there's a simpler way to do the same solely using regtest/timedtest.

Maybe I should have asked the following questions before proposing anything:

1) How does someone simulate a pow race situation without doing any
pow right now?
Does anybody try these things? How?

2) If I wanted to measure validation performance, to get the number of
peak tps that could be processed without taking block sides or network
latency into account, how would I do that? Has anybody tried this
before?

Re: [Bitcoin-development] Timed testing

[Mike Hearn]

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>
> 2) If I wanted to measure validation performance, to get the number of
> peak tps that could be processed without taking block sides or network
> latency into account, how would I do that? Has anybody tried this
> before?


You can just reindex/replay the chain. It's been done many times.

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Re: [Bitcoin-development] Timed testing

[Jorge Timón]

On 4/17/14, Mike Hearn <mike@plan99.net> wrote:
>>
>> 2) If I wanted to measure validation performance, to get the number of
>> peak tps that could be processed without taking block sides or network
>> latency into account, how would I do that? Has anybody tried this
>> before?
>
>
> You can just reindex/replay the chain. It's been done many times.

Yes, thank you. I guess that's what everybody is doing to measure
validation performance.
So I guess the timedtest mode doesn't make much sense, at most only as
the blocktime parameter defaulting to zero. If bool
MineBlocksOnDemand() gets refactored out of ChainParams into a
parameter (maybe just use genproclimit ?), you can have the periodic
block generation and the generation on demand reusing the same regtest
mode.

So it seems a new mode only makes sense if the -private mode makes
sense, which in turn only makes sense to include in bitcoind if it's
useful enough for the network attack simulations, which remains the
open question.

Re: [Bitcoin-development] Timed testing

[Gavin Andresen]

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On Thu, Apr 17, 2014 at 12:09 PM, Jorge Timón <jtimon@monetize.io> wrote:

> So it seems a new mode only makes sense if the -private mode makes
> sense, which in turn only makes sense to include in bitcoind if it's
> useful enough for the network attack simulations, which remains the
> open question.
>

Unless I misunderstood what your private mode does, you can get the same
effect with -regtest by just controlling nodes connectivity. For example:

Start 2 nodes, connected to each other. Mine a -regtest chain they both
agree on.

Restart them so they're not connected.  Have one mine normally,
have the other  mine... however you like to simulate some attack (deep
chain re-org, double-spend,
whatever).

To simulate launching the attack, connect them together again, let the two
chains compete and see
what happens.

-- 
--
Gavin Andresen

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Re: [Bitcoin-development] Timed testing

[Jorge Timón]

Thank you for all the explanations on how to use regtest to reproduce
the example scenarios.
It seems like a private mode wouldn't be particularly helpful for
testing so I won't create a pull request and will just work on the
private chains separately from bitcoind.

Going back to chainparam modes in general, I've heard Sipa complain
some times about regtest being too specific, arguing that some of the
behaviors should be specified as independent parameters instead of
chainparams attributes.
One example could be bool CChainPrams::MineBlocksOnDemand() (see
https://github.com/jtimon/bitcoin/commit/5bd4bc7f3694e46568c9276f0cb26402dfb99718
).
If that was an independent parameter that people set to true when
using regtest, the blocktime param I was proposing for -timedtest
could also be implemented as an independent parameter without any need
for a new mode.

It's not clear to me if the timedtest parameter would be useful for
bitcoind testing or not, but it's just something I've noticed while
playing with this part of the code.
Sipa, is this the kind of thing you refer to when you say regtest is
too specific?
Do you have any suggestion on how to solve the issue as part of PR 3824?

Well, any suggestions from anyone on how to improve PR 3824 are
welcomed, I was just asking specifically to sipa because as said it is
my understanding that he had some complaints about regtest and I think
this is something simple enough for me to start contributing to
bitcoind. Specially given that I was going to review all that part of
the code to externally write the private mode anyway.

-- 
Jorge Timón

http://freico.in/

Re: [Bitcoin-development] Timed testing

[Mark Friedenbach]

Not necessarily. Running a private server involves listening to the p2p
network for incoming transactions, performing validation on receipt and
organizing a mempool, performing transaction selection, and relaying
blocks to auditors - none of which is tested in a reindex.

A reindex would give you an optimistic upper bound though, if that's all
you care about.

On 04/17/2014 08:49 AM, Mike Hearn wrote:
>     2) If I wanted to measure validation performance, to get the number of
>     peak tps that could be processed without taking block sides or network
>     latency into account, how would I do that? Has anybody tried this
>     before?
> 
> You can just reindex/replay the chain. It's been done many times. 

Re: [Bitcoin-development] Timed testing

[Brian Hoffman]

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"So my question to the community is, how invasive is this to bitcoin's
source code?"

I'd say not very considering you have regression testing mode.


On Thu, Apr 17, 2014 at 8:25 AM, Jorge Timón <jtimon@monetize.io> wrote:

> I'm implementing a new testing mode that produces blocks
> periodically. You can get what I have so far here:
>
> https://github.com/jtimon/bitcoin/tree/timed
>
> It depends on pull request #3824 with some improvements on
> CChainParams, but after that the changes required to add this new
> mode are very small:
>
>
> https://github.com/jtimon/bitcoin/commit/445321928a143cb9a6f56777cbb7479dd32c3bcd
>
> I guess I need a new genesis block, different magic numbers, etc. So
> this is definitely not ready.
> You can run it like this:
>
> bitcoind -timedtest -gen=1 blocktime=2000
>
> blocktime defaults to 1000 milliseconds for timedtest mode and 0 for
> the rest of the modes.
>
> What could this testing mode be useful for?
>
> Basically, simulations.
> For example, you could run several nodes implementing different mining
> policies. Let's say I want to mine 50% of the blocks with standard policy,
> 25% with policy A and 25% with policy B. I can run 1 one for each of
> one with block times 2000, 1000 and 1000 respectively.
>
> Maybe I want to detect performance bottlenecks by stressing this mode
> with as many transaction as can be processed, maybe removing the
> block size limits in the simulations.
>
> But this still doesn't serve for hardfork or double-spend attacks
> simulations without calculating any pow, which would be another
> interesting feature for a new testing mode.
> I would like to implement the new mode following as the concept of
> private chains described in freimarkets:
>
> http://freico.in/docs/freimarkets.pdf
>
> https://github.com/jtimon/freimarkets/blob/master/doc/freimarkets_specs.org#private-ledgers
>
> https://github.com/jtimon/freimarkets/blob/master/doc/freimarkets_specs.org#off-chain-transactions
>
> I know this could be considered a "non-bitcoinish" application and
> therefore be controversial as discussed in PR 3824, so I want to keep
> the conversation focused on testing use cases useful to bitcoin itself
> only: additional changes can be implemented elsewhere.
> One way I think you could support chain races simulations by using a
> private mode could be the following:
>
> 1) The private mode works like the timed mode in how often it
>    produces blocks.
>
> 2) In private mode you replace the pow-related fields with a
>    blockPubkeyScript and a lastBlockSigScript fields. In the genesis
>    block, lastBlockSigScript is empty and the initial
>    blockPubkeyScript can be an optional parameter like blocktime. You
>    can set any valid script, probably p2sh, maybe with multisig to
>    allow different nodes to sign.
>
> 3) In this context, longer chains mean "more work". Another way to
>    see it is that all blocks just contain work==1 in them.
>
> So let's say we want to simulate an attack using 50% standard and 50%
> attacker blocks. You set up the private mode script to be a 1 of 2
> multisig and make each node sign always with the same private key
> (maybe an additional parameter).
> You make the attacker reject any blocks from height X that he hasn't
> signed himself to get the result you wanted: the standard node will
> produce blocks on top of the longest chain while the attacker will
> only hash on top of his own blocks.
>
> So my question to the community is, how invasive is this to bitcoin's
> source code?
> In my opinion, done properly could actually result (apart from getting
> the new features) in more readable code, not less, since you will
> probably need to make sure proof of work functionality is properly
> encapsulated during the implementation process (see PR 3839 for a first
> step on that direction).
> But, should I push a private mode to the core or just the timed one
> and implement the private mode elsewhere?
>
> Of course other comments on the parameters, defaults or any other
> design or implementation details are also welcomed.
>
> --
> Jorge Timón
>
> http://freico.in/
>
>
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