Constant CACHE_FLUSH_BYTES 

pub const CACHE_FLUSH_BYTES: u64 = _; // 4_194_304u64

The lazy pool buffers this much before it writes. Far under crate::exploded_arrow::FLUSH_BYTES on purpose: that 64 MiB buffer is sized for an indexer draining a pack, and a reader’s write-back holding 64 MiB per store is memory the box did not agree to spend.