Constant MAX_SEALED_BATCHES 

const MAX_SEALED_BATCHES: usize = _; // 8usize

Number of sealed batches that may wait to be created or indexed. One admission can seal two batches, the open batch before an append that would exhaust its positions and the append’s own batch, so the actor takes an append from its channel only while two more fit: a stalled object store holds callers back instead of growing the backlog.