Constant ACCESS_TRACE_DEFAULT_MAX_BYTES 

pub const ACCESS_TRACE_DEFAULT_MAX_BYTES: u64 = _; // 1_073_741_824u64

The bytes of header and records a trace holds at most when --access-trace-max-bytes is not given: 1 GiB. A record takes about 350 bytes, so this is some three million records; a run with more stops its trace there, without the end line, rather than fill the disk.