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From: Jeff Garzik <jgarzik@bitpay.com>
Date: Tue, 5 Aug 2014 13:48:18 -0400
Message-ID: <CAJHLa0O2wFq2Vs5Bes_8x1q_j0VC+U4DQkx=6GqT8w5e8Lh5Qg@mail.gmail.com>
To: Kaz Wesley <keziahw@gmail.com>
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Cc: Bitcoin Dev <bitcoin-development@lists.sourceforge.net>
Subject: Re: [Bitcoin-development] deterministic transaction expiration
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Glad this was brought up.

Transaction expiration is something that I have wanted to see happen in
bitcoin for a long, long time.  The user experience of unconfirming
transactions setting around in limbo is just horrible.  Bitcoin software by
necessity has gotten better about attaching fees so this sort of behavior
is uncommon, but that does not eliminate the problem.

Of course, we cannot presume that a transaction will truly disappear -- The
Internet Never Forgets -- but given a bit of mempool adjusting, we can
achieve the next best thing:  the majority of the network "forgets" the
transaction and becomes willing to relay a respend of some or all of the
inputs.  This uses existing client logic where the client must rebroadcast
a transaction until it is confirmed.

In general, if a transaction has not made it into a block within 144*X
blocks, there is _some_ reason it is getting rejected by the miners.

The mempool janitor is a garbage collector design.  This is inferior to the
"superblock" model described at
https://github.com/bitcoin/bitcoin/issues/3723   Other models can also
achieve similar results.

There are a lot of issues tied together here:  transaction expiration, the
desire to cap the mempool ram usage, scalability, DoS prevention, ...
mempool ties a lot together.

-- 
Jeff Garzik
Bitcoin core developer and open source evangelist
BitPay, Inc.      https://bitpay.com/

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<div dir=3D"ltr"><div><div><div><div>Glad this was brought up.<br><br></div=
>Transaction expiration is something that I have wanted to see happen in bi=
tcoin for a long, long time.=C2=A0 The user experience of unconfirming tran=
sactions setting around in limbo is just horrible.=C2=A0 Bitcoin software b=
y necessity has gotten better about attaching fees so this sort of behavior=
 is uncommon, but that does not eliminate the problem.<br>

<br></div>Of course, we cannot presume that a transaction will truly disapp=
ear -- The Internet Never Forgets -- but given a bit of mempool adjusting, =
we can achieve the next best thing:=C2=A0 the majority of the network &quot=
;forgets&quot; the transaction and becomes willing to relay a respend of so=
me or all of the inputs.=C2=A0 This uses existing client logic where the cl=
ient must rebroadcast a transaction until it is confirmed.<br>

<br></div>In general, if a transaction has not made it into a block within =
144*X blocks, there is _some_ reason it is getting rejected by the miners.<=
br><br></div>The mempool janitor is a garbage collector design.=C2=A0 This =
is inferior to the &quot;superblock&quot; model described at <a href=3D"htt=
ps://github.com/bitcoin/bitcoin/issues/3723">https://github.com/bitcoin/bit=
coin/issues/3723</a>=C2=A0=C2=A0 Other models can also achieve similar resu=
lts.<br>

<div><div class=3D"gmail_extra"><br></div><div class=3D"gmail_extra">There =
are a lot of issues tied together here:=C2=A0 transaction expiration, the d=
esire to cap the mempool ram usage, scalability, DoS prevention, ...=C2=A0=
=C2=A0 mempool ties a lot together.<br clear=3D"all">

<br>-- <br>Jeff Garzik<br>Bitcoin core developer and open source evangelist=
<br>BitPay, Inc. =C2=A0 =C2=A0 =C2=A0<a href=3D"https://bitpay.com/" target=
=3D"_blank">https://bitpay.com/</a>
</div></div></div>

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