The current logic for syncing headers may lead to lots of duplicate
getheaders requests being sent: If a new block arrives while the node
is in headers sync, it will send getheaders in response to the block
announcement. When the headers arrive, the message will be of maximum
size and so a follow-up request will be sent---all of that in addition
to the existing headers syncing. This will create a second "chain" of
getheaders requests. If more blocks arrive, this may even lead to
arbitrarily many parallel chains of redundant requests.
This patch changes the behaviour to only request more headers after a
maximum-sized message when it contained at least one unknown header.
This avoids sustaining parallel chains of redundant requests.
Note that this patch avoids the issues raised in the discussion of
https://github.com/bitcoin/bitcoin/pull/6821: There is no risk of the
node being permanently blocked. At the latest when a new block arrives
this will trigger a new getheaders request and restart syncing.
ActivateBestChain uses chainActive after releasing the lock; reorder operations
to move all access to synchronized object into existing LOCK(cs_main) block.
This will avoid sending more pointless INVs around updates, and
prevents using filter updates to timetag transactions.
Also adds locking for fRelayTxes.
By eliminating queued entries from the mempool response and responding only at
trickle time, this makes the mempool no longer leak transaction arrival order
information (as the mempool itself is also sorted)-- at least no more than
relay itself leaks it.
Previously we would assert that if every block in vBlockHashesToAnnounce is in
chainActive, then the blocks to be announced must connect. However, there are
edge cases where this assumption could be violated (eg using invalidateblock /
reconsiderblock), so just check for this case and revert to inv-announcement
instead.
Previously Bitcoin would send 1/4 of transactions out to all peers
instantly. This causes high overhead because it makes >80% of
INVs size 1. Doing so harms privacy, because it limits the
amount of source obscurity a transaction can receive.
These randomized broadcasts also disobeyed transaction dependencies
and required use of the orphan pool. Because the orphan pool is
so small this leads to poor propagation for dependent transactions.
When the bypass wasn't in effect, transactions were sent in the
order they were received. This avoided creating orphans but
undermines privacy fairly significantly.
This commit:
Eliminates the bypass. The bypass is replaced by halving the
average delay for outbound peers.
Sorts candidate transactions for INV by their topological
depth then by their feerate (then hash); removing the
information leakage and providing priority service to
higher fee transactions.
Limits the amount of transactions sent in a single INV to
7tx/sec (and twice that for outbound); this limits the
harm of low fee transaction floods, gives faster relay
service to higher fee transactions. The 7 sounds lower
than it really is because received advertisements need
not be sent, and because the aggregate rate is multipled
by the number of peers.
Break the circular dependency between main and txdb by:
- Moving `CBlockFileInfo` from `main.h` to `chain.h`. I think this makes
sense, as the other block-file stuff is there too.
- Moving `CDiskTxPos` from `main.h` to `txdb.h`. This type seems
specific to txdb.
- Pass a functor `insertBlockIndex` to `LoadBlockIndexGuts`. This leaves
it up to the caller how to insert block indices.
Previously we used the CInv that would be sent to the peer announcing the
transaction as the key, but using the txid instead allows us to decouple the
p2p layer from the application logic (which relies on this map to avoid
duplicate tx requests).
Currently, we're keeping a timeout for each requested block, starting
from when it is requested, with a correction factor for the number of
blocks in the queue.
That's unnecessarily complicated and inaccurate.
As peers process block requests in order, we can make the timeout for each
block start counting only when all previous ones have been received, and
have a correction based on the number of peers, rather than the total number
of blocks.
Two-line patch to make it possible to shut down bitcoind cleanly during
the initial ActivateBestChain.
Fixes#6459 (among other complaints).
To reproduce:
- shutdown bitcoind
- copy chainstate
- start bitcoind
- let the chain sync a bit
- shutdown bitcoind
- copy back old chainstate
- start bitcoind
- bitcoind will catch up with all blocks during Init()
(the `boost::this_thread::interruption_point` / `ShutdownRequested()`
dance is ugly, this should be refactored all over bitcoind at some point
when moving from boost::threads to c++11 threads, but it works...)
The "feefilter" p2p message is used to inform other nodes of your mempool min fee which is the feerate that any new transaction must meet to be accepted to your mempool. This will allow them to filter invs to you according to this feerate.
Peter Todd