Excessive WAL file accumulation fills disk when replication lags or archiving fails

WAL directory grows excessively when many WAL files accumulate due to replication lag or archive process failures. Without limits, WAL files can fill the disk entirely.

Check WAL directory size with `du -sh /var/lib/postgresql/14/main/pg_wal/` and count files with `ls /var/lib/postgresql/14/main/pg_wal/ | wc -l`. Investigate replication lag or archive issues. Set `max_wal_size = 2GB` and `min_wal_size = 1GB` to limit retention. Reduce checkpoint timeout with `checkpoint_timeout = 10min` for more frequent checkpoints. For non-replicated servers, set `wal_keep_size = 1GB` (PostgreSQL 13+) or `wal_keep_segments = 64` (PostgreSQL 12).