This commit fixes the following potential deadlock situation:
* Pathfinding holds a database lock and tries to obtain a mission control lock
via GetProbability
* ReportPaymentSuccess/ReportPaymentFail holds a mission control lock
and tries to obtain a database lock to store the payment result.
All of the other mission control exported functions acquire their locks
immediately, and do not lock in the subsequent unexported functions.
This commit moves the lock up for the report payment functions so that
mission control's config values are covered by this lock, in preparation
for allowing config to be updated at runtime. Moving this lock means
that we will hold the lock for the additional time it takes to store a
single result, AddResult, to the store.
We are going to use the config struct to allow getting and setting
of the mission control config in the commits that follow. Self node
is not something we want to change, so we move it out for better
separation.
Previously we only penalized the outgoing connections of a failing node.
This turned out not to be sufficient, because the next route sometimes
went into the same failing node again to try a different outgoing
connection that wasn't yet known to mission control and therefore not
penalized before.
Previously we used the a priori probability also for our own untried
channels. This led to local channels that had seen a success already
being prioritized over untried local channels. In some cases, depending
on the configured payment attempt cost, this could lead to the payment
taking a two hop route while a direct payment was also possible.
Probabilities are no longer returned for querymc calls. To still provide
some insight into the mission control internals, this commit adds a new
rpc that calculates a success probability estimate for a specific node
pair and amount.
This prepares for decoupling the result interpretation of a single
payment attempt from the information stored in mission control memory
on the history of a node pair. A planned follow-up where we store both
the last success and last failure requires this decoupling.
This commit changes mission control to partially base the estimated
probability for untried connections on historical results obtained in
previous payment attempts. This incentivizes routing nodes to keep all
of their channels in good shape.
Probability estimates are amount dependent. Previously we assumed an
amount, but that starts to make less sense when we make probability more
dependent on amounts in the future.
This commit changes the in-memory structure of the mission control
state. It prepares for calculation of a node probability. For this we
need to be able to efficiently look up the last results for all channels
of a node.
This commit modifies paymentLifecycle so that it not only feeds
failures into mission control, but successes as well.
This allows for more accurate probability estimates. Previously,
the success probability for a successful pair and a pair with
no history was equal. There was no force that pushed towards
previously successful routes.
This commit moves the payment outcome interpretation logic into a
separate file. Also, mission control isn't updated directly anymore, but
results are stored in an interpretedResult struct. This allows the
mission control state to be locked for a minimum amount of time and
makes it easier to unit test the result interpretation.
This commit converts several functions from returning a bool and a
failure reason to a nillable failure reason as return parameter. This
will take away confusion about the interpretation of the two separate
values.
Previously mission control tracked failures on a per node, per channel basis.
This commit changes this to tracking on the level of directed node pairs. The goal
of moving to this coarser-grained level is to reduce the number of required
payment attempts without compromising payment reliability.
Align naming better with the lightning spec. Not the full name of the
failure (FailIncorrectOrUnknownPaymentDetails) is used, because this
would cause too many long lines in the code.
If nodes return a channel policy related failure, they may get a second
chance. Our graph may not be up to date. Previously this logic was
contained in the payment session.
This commit moves that into global mission control and thereby removes
the last mission control state that was kept on the payment level.
Because mission control is not aware of the relation between payment
attempts and payments, the second chance logic is no longer based
tracking second chances given per payment.
Instead a time based approach is used. If a node reports a policy
failure that prevents forwarding to its peer, it will get a second
chance. But it will get it only if the previous second chance was
long enough ago.
Also those second chances are no longer dependent on whether an
associated channel update is valid. It will get the second chance
regardless, to prevent creating a dependency between mission control and
the graph. This would interfer with (future) replay of history, because
the graph may not be the same anymore at that point.
This commit exposes the three main parameters that influence mission
control and path finding to the user as command line or config file
flags. It allows for fine-tuning for optimal results.
Previously every payment had its own local mission control state which
was in effect only for that payment. In this commit most of the local
state is removed and payments all tap into the global mission control
probability estimator.
Furthermore the decay time of pruned edges and nodes is extended, so
that observations about the network can better benefit future payment
processes.
Last, the probability function is transformed from a binary output to a
gradual curve, allowing for a better trade off between candidate routes.
