const SUBSCRIBE_MESSAGE_OVERHEAD_BYTES: usize = 1024;Expand description
Overhead charged to every queued message on top of its payload.
A frontier-only advance carries no rows, so its payload is zero bytes. It
still costs real memory: a node in the unbounded channel and an entry in
footprints. Charging payload alone would leave the backlog flat while
those two grow without bound, so the retire check would never trip on a
stalled client that only receives progress messages. The fixed charge makes
the budget bound message count as well as payload bytes.