With few exceptions, servers will typically receive multiple copies
of any given message from its directly connected peers. For servers
with several peers this can impact the processing latency and force
it to do redundant work. Proposal and validation messages are often
relayed with extremely high redundancy.
This commit, if merged, introduces experimental code that attempts
to optimize the relaying of proposals and validations by allowing
servers to instruct their peers to "squelch" delivery of selected
proposals and validations. Servers making squelching decisions by
a process that evaluates the fitness and performance of a given
server and randomly selecting a subset of the best candidates.
The experimental code is presently disabled and must be explicitly
enabled by server operators that wish to test it.
Do not process a transaction received from a peer if it has
been processed within the past ten seconds.
Increase the number of transaction handlers that can be in
flight in the job queue and decrease the relative cost for
peers to share transaction and ledger data.
Additionally, make better use of resources by adjusting the
number of threads we initialize, by reverting commit
68b8ffdb63.
Performance counter modifications:
* Create and display counters to track:
1) Pending transaction limit overruns.
2) Total peer disconnections.
3) Peers disconnections due to resource consumption.
Avoid a potential double-free in Json library.
* If the transaction can't be queued, recover to the open ledger once,
and drop it on the next attempt.
* New result codes for transactions that can not queue.
* Add minimum queue size.
* Remove the obsolete and incorrect SF_RETRY flag.
* fix#2215
