Constant MAX_ROW_GROUPS_PER_FILE 

pub(crate) const MAX_ROW_GROUPS_PER_FILE: usize = 30_000;

Maximum row groups in one file before it is rotated.

Parquet’s hard limit is 32,767 row groups per file. With ROWS_PER_ROW_GROUP rows per group a normal rotation window never comes close; this is a safety limit that starts a new file well before the hard limit.