If Postgres logical replication is enabled via pglogical extension, below query can be used to check the size WAL Folder. select sum(size) from pg_ls_waldir(); (Response to the query is in Bytes)

This is the folder where the WAL logs are stored, which is utilized for postgres data replication from master to slave. In case there is any lag or problems with replication the logs will get accumulating in the folder, spiking the disk storage and can cause downtime of the database it self.