Add Comprehensive Guide to Snowflake Data Quality Monitoring

[sfc-gh-yostrinsky]

Summary

A new example-led guide to Data Quality Monitoring. Draft, opened for review.

• Shape: a small shared setup, then self-contained recipes. A reader can run any single example on its own without working through the others, so the guide works as a reference you return to rather than a walkthrough you complete once.
• Dataset: IoT sensor telemetry (DQ_EXAMPLES) with seven deliberately seeded defects, each named openly so every check is verifiable.
• Coverage: the system metric catalogue and a decision table, twelve failure-mode recipes, custom metrics, schema-wide monitoring, AI-suggested checks, anomaly detection, remediation, notifications, a circuit breaker, layer strategy, quality as code, and cost.
• SQL and UI in parallel. Snowsight paths sit alongside the SQL rather than being mentioned in passing.

Provenance

Every SQL block was run against a live Enterprise account and the result tables are real output, not illustrative. Three behaviours the guide calls out because they were found by running it:

• FRESHNESS can return a negative value when a future-dated row is the newest timestamp, so a freshness check alone can be defeated by one bad timestamp. The guide pairs it with the clock-skew check.
• SYSTEM$EVALUATE_DATA_QUALITY_EXPECTATIONS does not record its result; the _PERSIST_RESULT variant does. Anything reading monitoring history needs the latter.
• UNSET DATA_METRIC_SCHEDULE reverts to the default hourly cadence rather than suspending monitoring. The suspend is SET DATA_METRIC_SCHEDULE = ''.

The circuit breaker was proven end to end (alert TRIGGERED, downstream task suspended), and uses an ALERT object because the native notification settings have no action hook.

Known gaps before this leaves draft

• Screenshots — four TODO: screenshot placeholders mark what each image must show
• Final review pass by the Data Quality team
• The "Checks as Code" section describes the declarative path in prose; its SQL needs validating inside a real DCM project before it is added

Test plan

• Every SQL block executed against a live Enterprise account (10.31.101)
• All seven seeded defects confirmed detectable, one each
• Circuit breaker verified: alert fired, downstream task suspended
• Result tables in the guide match real query output
• Snowsight click paths walked against a live UI

[sfc-gh-yostrinsky]

Superseded by #3542 — moved from a fork branch to a branch in this repository so the staging preview workflow can run, and rebased onto current master. Preview is live there.