when turning on logical replication postgres keeps all wal files until they are also applied to the downstream consumer. if you don't use logical replication they get cleaned up by setting wal_keep_segments and max_wal_size (which have a sane value so there is nothing to bother)

btw. a good idea is to keep these wal files or at least archive them with a basebackup, because it enables PITR recovery (https://www.postgresql.org/docs/9.3/continuous-archiving.htm...) via wal-g or wal-e.

btw. the bigger mistake here is that a lot of people do not monitor their database size, which is a huge problem.

edit: ah and wal files are always 16mb (unless compiled differently)

> There will always be at least one WAL segment file, and will normally not be more than (2 + checkpoint_completion_target) * checkpoint_segments + 1 or checkpoint_segments + wal_keep_segments + 1 files. Each segment file is normally 16 MB (though this size can be altered when building the server). You can use this to estimate space requirements for WAL. Ordinarily, when old log segment files are no longer needed, they are recycled (renamed to become the next segments in the numbered sequence). If, due to a short-term peak of log output rate, there are more than 3 * checkpoint_segments + 1 segment files, the unneeded segment files will be deleted instead of recycled until the system gets back under this limit.