>
> 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.