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Date: Sat, 28 Dec 2013 14:46:05 +0000
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From: Mike Hearn <mike@plan99.net>
To: Jeremy Spilman <jeremy@taplink.co>
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Cc: "bitcoin-development@lists.sourceforge.net"
	<bitcoin-development@lists.sourceforge.net>
Subject: Re: [Bitcoin-development] Access to Mempool
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>
> I was reading there are some commands to access a peer's mempool state.
> The purpose being to allow miners to recover faster after a reboot, I
> think?
>

The "mempool" command allows nodes to request the contents of a peers
memory pool, yes.

It is currently used by SPV clients to find transactions that were
broadcast before they were started up (but not yet confirmed).


> Reading peer mempool definitely allows recovering faster after a reboot.
> So does persisting mempool in a database locally.


0.9 has code to save the mempool to disk.


> But what can you learn about a node from its mempool? Basically, are there
> distinguishing
> features in the mempool, or could there be?
>

Er, you mean, distinguishing features beyond the nodes IP address?

The contents of the mempool may vary depending on when the node was started
and what it saw at what times. I guess it's distinguishing in a way, but
not in any important way. Nodes are not intended to be completely
indistinguishable, just indistinguishable enough that it doesn't matter
which you connect to.


> Are there transactions you can receive which go into your own mempool but
> which you don't forward?


I don't think so, unless there are quirks to do with sendrawtransaction
RPCs or strangely crafted wallet spends. Normally if a tx is in the mempool
it will be relayed.


> By the way, are there recommended places to go to compare features
> implemented by different wallet software?
>

I don't know of any such place, but I'm sure people have compiled tables
somewhere.

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<div dir=3D"ltr"><div class=3D"gmail_extra"><div class=3D"gmail_quote"><blo=
ckquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #c=
cc solid;padding-left:1ex">I was reading there are some commands to access =
a peer&#39;s mempool state.<br>

The purpose being to allow miners to recover faster after a reboot, I<br>
think?<br></blockquote><div><br></div><div>The &quot;mempool&quot; command =
allows nodes to request the contents of a peers memory pool, yes.</div><div=
><br></div><div>It is currently used by SPV clients to find transactions th=
at were broadcast before they were started up (but not yet confirmed).=C2=
=A0</div>
<div>=C2=A0</div><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8=
ex;border-left:1px #ccc solid;padding-left:1ex">Reading peer mempool defini=
tely allows recovering faster after a reboot.<br>
So does persisting mempool in a database locally.</blockquote><div><br></di=
v><div>0.9 has code to save the mempool to disk.</div><div>=C2=A0</div><blo=
ckquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #c=
cc solid;padding-left:1ex">
 But what can you learn=C2=A0about a node from its mempool? Basically, are =
there distinguishing<br>
features in the mempool, or could there be?<br></blockquote><div><br></div>=
<div>Er, you mean, distinguishing features beyond the nodes IP address?=C2=
=A0</div><div><br></div><div>The contents of the mempool may vary depending=
 on when the node was started and what it saw at what times. I guess it&#39=
;s distinguishing in a way, but not in any important way. Nodes are not int=
ended to be completely indistinguishable, just indistinguishable enough tha=
t it doesn&#39;t matter which you connect to.</div>
<div>=C2=A0</div><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8=
ex;border-left:1px #ccc solid;padding-left:1ex">Are there transactions you =
can receive which go into your own mempool but<br>
which you don&#39;t forward?</blockquote><div><br></div><div>I don&#39;t th=
ink so, unless there are quirks to do with sendrawtransaction RPCs or stran=
gely crafted wallet spends. Normally if a tx is in the mempool it will be r=
elayed.</div>
<div>=C2=A0</div><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8=
ex;border-left:1px #ccc solid;padding-left:1ex">By the way, are there recom=
mended places to go to compare features<br>
implemented by different wallet software?<br></blockquote><div><br></div><d=
iv>I don&#39;t know of any such place, but I&#39;m sure people have compile=
d tables somewhere.</div></div></div></div>

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