The Inflights type has limits on the message size and the number of inflight
messages. However, a single large entry that exceeds the size limit can still
be sent. In combination with the max messages count limit, many large messages
can be sent in a row and overflow the receiver. In effect, the "max" values act
as "target" rather than hard limits.
This commit adds an additional soft limit on the total size of inflight
messages, which catches such situations and prevents the receiver overflow.
Signed-off-by: Pavel Kalinnikov <pavel@cockroachlabs.com>
Recent refactoring to the String() method of `Progress` hit an NPE
because we return nil Inflights as part of the Raft status. Just
fix this at the source and properly populate the Raft status instead
of teaching String() to ignore nil. A real Progress always has a
non-nil Inflights.
Mechanically extract `progressTracker`, `Progress`, and `inflights`
to their own package named `tracker`. Add lots of comments in the
progress, and take the opportunity to rename and clarify various
fields.
