Troubleshooting

Symptom-led diagnosis for a NYXDB node, with the system relation that explains each symptom.

Symptom	Where to look
Writes slow down	`pressure_stalled` and `accepting` in `system.tablets`; `rejected_mutations` in `system.storage`.
WAL keeps growing	`system.wal_reclamation_blockers`.
A derived table lags	`system.transformation_revisions` and `system.derived_lineage`.
A stream falls behind	`system.psi_streams`: demand, queued frames and lag per subscription.
A query runs long	`system.queries` and `system.query_stats`.
A federation source is not ready	`system.sources`.