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Date: Thu, 26 Apr 2012 14:00:59 -0400
From: Alan Reiner <etotheipi@gmail.com>
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Subject: Re: [Bitcoin-development] Trusted identities
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On 04/26/2012 01:30 PM, Peter Todd wrote:
>
>> More difficulty shortens the safe time we can transact large volumes in,
>> which is good for the network.
>>
>> I'm not sure of the current implementation of replacement transactions, can
>> anyone on the core team speak to this? Can I replace transactions, or is
>> that part of the spec unimplemented or deprecated right now?
> My understanding is it's completely disabled.

Went on a scavenger hunt with Gavin a couple weeks concerning tx 
replacement.  The conclusion was that if,
(1) Transaction has lock-time in the future  AND
(2) Transaction has non-maximum sequence number

Then the transaction will both propagate and be accepted into nodes' 
memory pools, but will not go into any block until locktime expires.  If 
the lock-time is in the past OR sequence number on all TxIns is 
0xffffffff, then it will be immediately valid and included in the 
blockchain.

But the actual "replacement" mechanism is disabled.  Therefore, the 
nodes accept the tx as if it's replaceable, but don't allow it to be 
replaced.  This means that it is effectively replaceable *once*, but 
only if you inject a final transaction into the blockchain.   You can't 
broadcast a final version of the same tx, because it will conflict with 
the non-final one sitting in all the other nodes' memory pools.  You 
need a miner to agree to remove the non-final tx from their memory pool 
and specifically include your replacement.

-Alan


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    On 04/26/2012 01:30 PM, Peter Todd wrote:
    <blockquote cite="mid:20120426173000.GB16099@savin.lan" type="cite"><br>
      <blockquote type="cite">
        <pre wrap="">More difficulty shortens the safe time we can transact large volumes in,
which is good for the network.

I'm not sure of the current implementation of replacement transactions, can
anyone on the core team speak to this? Can I replace transactions, or is
that part of the spec unimplemented or deprecated right now?
</pre>
      </blockquote>
      <pre wrap="">
My understanding is it's completely disabled.
</pre>
    </blockquote>
    <br>
    Went on a scavenger hunt with Gavin a couple weeks concerning tx
    replacement.&nbsp; The conclusion was that if,<br>
    (1) Transaction has lock-time in the future&nbsp; AND<br>
    (2) Transaction has non-maximum sequence number<br>
    <br>
    Then the transaction will both propagate and be accepted into nodes'
    memory pools, but will not go into any block until locktime
    expires.&nbsp; If the lock-time is in the past OR sequence number on all
    TxIns is 0xffffffff, then it will be immediately valid and included
    in the blockchain.<br>
    <br>
    But the actual "replacement" mechanism is disabled.&nbsp; Therefore, the
    nodes accept the tx as if it's replaceable, but don't allow it to be
    replaced.&nbsp; This means that it is effectively replaceable <b>once</b>,
    but only if you inject a final transaction into the blockchain. &nbsp;
    You can't broadcast a final version of the same tx, because it will
    conflict with the non-final one sitting in all the other nodes'
    memory pools.&nbsp; You need a miner to agree to remove the non-final tx
    from their memory pool and specifically include your replacement.<br>
    <br>
    -Alan<br>
    <br>
    <br>
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