Defer inserting into maprelay until just before relaying.

[gmaxwell]

This reduces the rate of not founds by better matching the far
end expectations, it also improves privacy by removing the
ability to use getdata to probe for a node having a txn before
it has been relayed.

[sipa]

More efficient:

auto ret = mapRelay.insert(std::make_pair(inv.hash, tx));
if (ret.second) {
    vRelayExpiration.push_back(std::make_pair(GetTime() + 16 * 60, inv.hash));
}

[gmaxwell]

Done.

[MarcoFalke]

Looks like comparison tool triggers a POTENTIAL DEADLOCK DETECTED

[gmaxwell]

@MarcoFalke Yep. It was an actual inversion with the vSend lock, it's fixed.

[laanwj]

Concept ACK

Nit: After this mapRelay is no longer used in net at all. It could become local to main.

[gmaxwell]

@laanwj good catch with the nit, I've removed it from net.cpp/net.h.

[sipa]

utACK d9d1f2e

[theuni]

ut ACK d9d1f2e

[paveljanik]

@gmaxwell Can you please be more explicit in the commit message? In "This reduces the rate of not founds", "This" means "this PR" or you mean the 15-> 16 minutes change (why not separate commit, BTW)?

What is the logic behind 15 -> 16 anyway?

[gmaxwell]

@paveljanik "better matching far end expectations"-- the far end retries on a two minute interval; 15 minutes is dead between counts-- starting the counter before the transaction has been offered to anyone also makes it more likely to time out first.

[arowser]

Can one of the admins verify this patch?

[sipa]

@gmaxwell I guess that can use some comment in the code?

[gmaxwell]

I changed it back to 15 minutes, -- I think the time there should be adjusted but it can be done in another pull that reworks the mapaskfor handling a bit.

[gmaxwell]

Rebased.

[sipa]

Lightly tested ACK. Setup: two mainnet full nodes with this patch (A publicly reachable, B -connect'ed to A) and a lightweight node C (connected to the public network). Tested block synchronization/relay of B from A, relay of transactions to from A to B, relay of newly created transactions by B and C through A. Nothing unusual.