@gmaxwell was asking about testing. This was tested successfully with a one-line pynode patch (pynode HEAD deb07f51435cd0d18596bddfee28e337a5a6454e). pynode issues 'mempool' at startup, and fills its own mempool with the returned results.

--- a/node.py
+++ b/node.py
@@ -238,6 +238,7 @@ class NodeConn(asyncore.dispatcher):
                        self.send_message(msg_verack(self.ver_send))
                        if self.ver_send >= CADDR_TIME_VERSION:
                                self.send_message(msg_getaddr(self.ver_send))
+                       self.send_message(msg_mempool())
                        self.send_getblocks()

Random thought: miners may want this, to "prime the pump" after restarting their bitcoind. There is the incentive to capture every fee-paying transactions, after all.

Automatic sanity-testing: PASSED, see http://jenkins.bluematt.me/pull-tester/05a85b2b38d516a8701f684fcd2ab99f3e5b462d for binaries and test log.

ACK on the changes, but maybe there must at least be some discussion about adding this, and the protocol version change involved. An alternative would be using a service bit (I don't personally think that is preferable), but people may have other opinions.

I would expect the startup sequence to also send a mempool command to another node, in case it reports protocol version 60002 or higher?

Automatic sanity-testing: PASSED, see http://jenkins.bluematt.me/pull-tester/05f891636199c36e1639fb95f5e92445eea9e97f for binaries and test log.

Specification: https://en.bitcoin.it/wiki/BIP_0035

ACK