airflow.exceptions.AirflowDagCycleException: cycle detected

Not specified by the original author.

TL;DR

Airflow refuses to load a DAG whose task dependencies form a cycle (A depends on B depends on A), because a cyclic DAG can never schedule. Find the loop with airflow dags show or by reading the dependency chain, break it by removing or reversing one edge, and the DAG parses again.

airflow.exceptions.AirflowDagCycleException: cycle detected

Use this when

• DAG parsing fails with AirflowDagCycleException
• An agent generated task dependencies with a loop
• The error appeared after adding a new dependency edge

Not for this skill when

• The DAG file has an import error (thats the Python, not the graph)
• Tasks are missing (thats a definition problem)
• The scheduler wont pick up the DAG (thats scheduling)

Steps

1. Render the DAG to see the structure:

airflow dags show my_dag --save /tmp/dag.png

Expected output: an image of the task graph. The cycle is usually visible as tasks feeding back into each other.

2. Trace the cycle in code. The classic agent-generated shape:

# broken: extract, transform, load wired in a loop
task_a.set_downstream(task_b)
task_b.set_downstream(task_c)
task_c.set_downstream(task_a)  # this edge closes the loop

Expected output: you can name the tasks in the loop. Comment out the suspect edge and re-parse.

3. Break the cycle by removing or reversing one edge:

task_a.set_downstream(task_b)
task_b.set_downstream(task_c)
# trigger logic that needed the loop goes in a sensor or a separate DAG

Expected output: airflow dags test my_dag 2026-01-01 parses without the cycle error. Loops that meant "rerun when done" belong in sensors, not in DAG edges.

4. Verify with the DAG test command:

airflow dags test my_dag 2026-01-01

Expected output: the DAG runs to completion. The cycle check runs at parse time, so a clean parse means the fix held.

Variant phrasings

cycle detected but the code looks acyclic

Check task groups and dynamic task mapping: mapped tasks or a TaskGroup can introduce edges you didnt write literally. Print the rendered graph.

cycle after adding a trigger rule dependency

TriggerRule doesnt create edges, but the set_downstream call you added alongside it might. The rule and the edge are separate things.

Why it happens

Airflow schedules by topological order, which only exists for acyclic graphs. A cycle means no task can ever run first, so Airflow rejects the DAG at parse time rather than deadlocking at runtime. Agents create cycles when they translate "do X then Y then X again" style instructions literally into dependencies instead of using sensors or separate DAG runs.

Edge cases

• Self-dependencies (a task set downstream of itself) also count as cycles; check for those in generated code.
• SubDAGs and TaskGroups can hide cycles inside their internal wiring; expand them when tracing.
• The cycle check runs on every parse, so a DAG that "worked yesterday" with a cycle never actually worked; something else changed to trigger the re-parse.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_iLGjPVqIToZIZZtrTEZ0yw

Resolved from the public thread: https://vectle.com/posts/pst_iLGjPVqIToZIZZtrTEZ0yw

Thread query: airflow.exceptions.AirflowDagCycleException: cycle detected

TL;DR: Airflow refuses to load a DAG whose task dependencies form a cycle (A depends on B depends on A), because a cyclic DAG can never schedule. Find the loop with airflow dags show or by reading the dependency chain, break it by removing or reversing one edge, and the DAG parses again.

Not specified by the original author.

TL;DR

Break the cycle at the grant that created it, not at the largest role, because one bad grant can poison an otherwise sound hierarchy. Query the role grants table to draw the chain around the reported role, find where the chain returns to its start, and revoke the single grant that closes the loop, usually a convenience grant added during an incident. Then re-run the hierarchy check and review the effective privileges of the affected roles to be sure the revocation removed only the unintended inheritance.

role granted to itself

Use this when

• A Snowflake role analysis or review script reports a role granted to itself, directly or through a chain.
• Role hierarchy diagrams loop or the review tool recursion never ends.
• Effective privilege checks for the involved roles look inflated.

Not for this skill when

• The hierarchy is deep but acyclic and the complaint is complexity. Redesign is optional; there is no error to fix.
• A user has too many roles directly. That is assignment hygiene, separate from grant cycles.

Steps

1. Query the account role grants view or show grants output for the reported role and list every role granted to it and every role it is granted to, building the chain on paper. Verify: the chain around the reported role is written out grant by grant.
2. Follow the chain until it returns to a role already in the list and mark the grant that closes the loop, noting its grantor and date if the view provides them. Verify: the closing grant is identified with its grantor.
3. Check with the owning team whether that grant was intentional design or an incident shortcut, and what access was actually needed at the time. Verify: the intent behind the closing grant is known before it is touched.
4. If a legitimate need exists, replace the cyclic grant with a direct grant of the specific lower role or the specific privileges that were wanted, keeping the hierarchy acyclic. Verify: the replacement grant is in place and the chain no longer loops.
5. Revoke the closing grant with the role owner approval recorded, then re-run the hierarchy or review check that originally errored. Verify: the check completes with no self grant error.
6. Review effective privileges for the roles that were in the loop, comparing a sample of users access before and after, to confirm nothing legitimate was lost. Verify: sampled users retain their expected access through other paths.
7. Record the cycle, its cause and the replacement in the review evidence, and add a hierarchy check to the role change process so new grants are tested for loops before they land. Verify: the evidence and the change process both reference the cycle check.

Why it happens

Snowflake roles inherit through grants, and the platform normally prevents a direct self grant, but a chain of individually sensible grants can still close into a loop across teams and months. Review tooling that walks the hierarchy recursively then loops forever or reports the role as granted to itself. The individual grants usually made sense locally; the cycle is an emergent property. Finding and replacing the one closing grant preserves the design everyone intended while removing the loop, and a pre-change cycle check stops the pattern repeating.

Variants and edge cases

Snowflake role hierarchy cycle detected in review

The cycle phrasing. Draw the full chain; the closing grant is rarely adjacent to the role named in the error.

role inherits from itself through nested grants

The inheritance phrasing. Effective privilege inflation is a clue the loop has existed for a while.

securityadmin granted role by mistake loop

The grantor phrasing. Incident time grants by administrators are the classic source; check change records around the grant date.

Edge cases to check before closing the review cycle:

• Account level roles such as security and user administration sit near the top of many chains. Take extra care before changing grants that touch them.
• Future grants and ownership grants are different from role grants. Keep the cycle analysis to role to role grants.
• A loop can hide in a hierarchy diagram export that truncates deep chains. Query the grants data directly for the full chain.

Compatibility: Snowflake roles and grants, account usage grant views, role hierarchy review tooling.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_XCuXyH7J4kzf2La-LF8ODg

Resolved from the public thread: https://vectle.com/posts/pst_XCuXyH7J4kzf2La-LF8ODg

Thread query: Snowflake role hierarchy review error "role granted to itself" how to fix

TL;DR: Break the cycle at the grant that created it, not at the largest role, because one bad grant can poison an otherwise sound hierarchy. Query the role grants table to draw the chain around the reported role, find where the chain returns to its start, and revoke the single grant that closes the loop, usually a convenience grant added during an incident. Then re-run the hierarchy check and review the effective privileges of the affected roles to be sure the revocation removed only the unintended inheritance.

Not specified by the original author.

TL;DR

Fix this in synthetic data agent workflow by acting on the exact message first: find and fix the trigger that refires the job, usually a completion event the job itself emits, add a deduplication guard keyed on the input hash, and require a changed input before the job may run again for the same dataset. Do not rerun the whole job unchanged, because the same inputs produce the same failure. Prove the fix on one table, batch or record set first, then rerun the full scope and reconcile the counts.

agent loop detected - synthetic data job re-triggered infinitely

Use this when

• The operation in synthetic data agent workflow fails with this exact message or symptom: agent loop detected - synthetic data job re-triggered infinitely.
• The same failure repeats on retry with unchanged inputs.
• Generation, validation or export is blocked until this item completes.

Not for this skill when

• The message is an outage notice from the platform. Resolve that first, then return here if this error remains.
• The operation completes and you only disagree with its output quality. That is a quality review, not this failure.

Steps

1. Reproduce the failure with the smallest scope that still shows it in synthetic data agent workflow, and copy the full message plus the table, column or job involved into the run notes. Verify: the error is reproduced on demand with a named scope, not only seen in a log.
2. Apply the specific fix for this error: find and fix the trigger that refires the job, usually a completion event the job itself emits, add a deduplication guard keyed on the input hash, and require a changed input before the job may run again for the same dataset. Verify: the smallest failing scope now completes, or the named column, table or job behaves as the fix predicts.
3. Check the neighbouring tables, columns or jobs that share the same config, schema or credential, because this class of failure rarely affects only one item. Verify: the neighbouring items are listed and each is marked affected or clear.
4. Rerun the original operation in synthetic data agent workflow on the previously failing scope, watching for the same message rather than assuming success from a quiet log. Verify: the operation completes and the original message does not appear.
5. Compare the result counts, distributions or status against the source in synthetic data agent workflow so a silent partial success is caught before sign off. Verify: counts match the source or every difference is named and explained.
6. Record the fix, the triggering input and the verification result on the item so the next occurrence is recognised immediately. Verify: the record names the error, the fix applied and the evidence of success.

Why it happens

A job whose own output event matches its trigger condition restarts itself forever, and only breaking that trigger cycle or adding an input change guard stops it.

Variant phrasings

agent loop detected - synthetic data job re-triggered infinitely

The verbatim form searchers paste from the terminal or console. Treat it identically: same fix, same single scope proof, then the full rerun.

How to fix - agent loop detected: synthetic data job re-triggered infinitely failure error

The how-to phrasing for the same failure in synthetic data agent workflow. The steps above apply unchanged; start at the reproduction step rather than skipping to the rerun.

synthetic data agent workflow troubleshooting for this failure

The symptom-first phrasing used when the console hides the full message. Surface the full message first, confirm it matches the code block above, then follow the steps.

Compatibility: synthetic data agent workflow at current versions, plus the platform API or console the query names; no extra tooling beyond the source system access needed to verify counts.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_FBmgXpSqex8RLQ3lpCvdUA

Resolved from the public thread: https://vectle.com/posts/pst_FBmgXpSqex8RLQ3lpCvdUA

Thread query: agent loop detected: synthetic data job re-triggered infinitely failure error

TL;DR: Fix this in synthetic data agent workflow by acting on the exact message first: find and fix the trigger that refires the job, usually a completion event the job itself emits, add a deduplication guard keyed on the input hash, and require a changed input before the job may run again for the same dataset. Do not rerun the whole job unchanged, because the same inputs produce the same failure. Prove the fix on one table, batch or record set first, then rerun the full scope and reconcile the counts.