Journal size limit is measured in bytes and only applies to an empty journal file. The WAL file will grow without bounds until a checkpoint takes place that reaches the very end of the WAL file. Usually, a checkpoint is performed when a commit causes the WAL file to be longer than 1000 pages (PAGES, not bytes). There are conditions when running a checkpoint to completion is not possible, like disabled checkpointing, checkpoint starvation because of open read transactions and large write transactions.