ISTAT: verify recurring HTTP 500 / constraint timeout on 121_331 and 41_269_DF_DCIS_INCIDENTISTR1_1

[aborruso]

Context

Investigating an external report claiming broken dimension codelists on ISTAT. That specific claim was debunked (CL_TIPO_DATO7 does contain the air transport codes FLIGHT/PASS/PAX/PDI/PEM/PATR — the report misread a shared codelist). But two real ISTAT-side issues showed up while verifying, on the same day (2026-07-06):

Observed

1. 121_331 (Trasporto aereo, datastructure DCSC_INDTRAEREO, 8 dimensions)

   • opensdmx info 121_331 --provider istat → Could not fetch bulk constraints at catalog time: The read operation timed out
   • Every opensdmx get 121_331 ... attempt → HTTP 500, even filtered to DATA_TYPE=PASS + REF_AREA=IT + explicit period. Likely the remaining wildcard cross-product (airports × service type × nation vector × country) is still too large for ISTAT to serve.

2. 41_269_DF_DCIS_INCIDENTISTR1_1 (road accidents — the known-good dataflow used in scripts/monitor_latency.py)

   • opensdmx get 41_269_DF_DCIS_INCIDENTISTR1_1 --start-period 2022 --end-period 2023 --last-n 1 -y → HTTP 500 on datastructure/ALL/DCIS_INCIDENTISTR1
   • This dataflow is normally reliable (it's our latency-monitor canary), so this may indicate general ISTAT-side degradation that day rather than something specific to 121_331.

Why it matters

availableconstraint timeouts on ISTAT are already known (see 09f9009 fix(monitor): skip constraints for istat), but this is the first time we've seen the data endpoint itself return 500 on a previously-reliable dataflow.

To verify

• Re-run both queries on a different day to check if it's transient ISTAT degradation vs. a 121_331-specific issue (query too broad).
• If 121_331 reproducibly 500s even on narrow queries, check whether a minimal single-series query (single airport + single service type) succeeds — to confirm it's a cross-product size issue and not a dataflow-specific server bug.
• If 41_269_DF_DCIS_INCIDENTISTR1_1 keeps failing, check output/latency.jsonl for a pattern before opening a report to ISTAT.
• Consider whether opensdmx should surface a clearer message than raw HTTP 500 when a query's cross-product is likely too large for ISTAT to serve.