fix(clickhouse): writable_events doesn't exist on DATA

[orian]

Problem

migration cannot be applied

Changes

remove DATA node as a target for alter table on writable_events

[greptile-apps]

Comments Outside Diff (1)

1. posthog/clickhouse/migrations/0267_wire_up_existing_dmat_string_columns.py, line 108-119 (link)

   The comment still says "writable_events lives on DATA in every install" but the fix establishes the opposite for cloud: on cloud, writable_events only exists on INGESTION_EVENTS, not DATA. A reader following the comment will be confused about why DATA was removed from the cloud case.

   Prompt To Fix With AI

   This is a comment left during a code review.
   Path: posthog/clickhouse/migrations/0267_wire_up_existing_dmat_string_columns.py
   Line: 108-119
   
   Comment:
   The comment still says "writable_events lives on DATA in every install" but the fix establishes the opposite for cloud: on cloud, `writable_events` only exists on `INGESTION_EVENTS`, not `DATA`. A reader following the comment will be confused about why `DATA` was removed from the cloud case.
   
   
   
   How can I resolve this? If you propose a fix, please make it concise.

   Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!

Prompt To Fix All With AI

Fix the following 1 code review issue. Work through them one at a time, proposing concise fixes.

---

### Issue 1 of 1
posthog/clickhouse/migrations/0267_wire_up_existing_dmat_string_columns.py:108-119
The comment still says "writable_events lives on DATA in every install" but the fix establishes the opposite for cloud: on cloud, `writable_events` only exists on `INGESTION_EVENTS`, not `DATA`. A reader following the comment will be confused about why `DATA` was removed from the cloud case.

```suggestion
# writable_events lives on INGESTION_EVENTS on cloud (added by migration 0232) and on
# DATA on non-cloud installs. The two are mutually exclusive: DATA does not host
# writable_events on cloud, so we target only the role that actually has the table.
# It is a Distributed engine table (not sharded, not replicated), so neither flag
# applies — explicit False is required to satisfy the migration convention check.
operations += [
    run_sql_with_exceptions(
        ALTER_TABLE_ADD_DMAT_STRING_COLUMNS(
            table="writable_events",
            start=_STRING_RANGE_START,
            end_exclusive=_STRING_RANGE_END,
        ),
        node_roles=([NodeRole.INGESTION_EVENTS] if _is_cloud else [NodeRole.DATA]),
```

_{Reviews (1): Last reviewed commit: "writable_events doesn't exist on DATA" | Re-trigger Greptile}

[github-actions]

🎭 Playwright report

❌ 2 failed tests:

• create experiment via wizard, add metrics, and launch (chromium)
• Deleting a dashboard navigates to the dashboards list (chromium)

These issues are not necessarily caused by your changes.
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[deployment-status-posthog]

Deploy status

Environment	Status	Deployed At	Workflow
dev	✅ Deployed	2026-06-01 23:34 UTC	Run
prod-us	✅ Deployed	2026-06-02 10:18 UTC	Run
prod-eu	✅ Deployed	2026-06-02 10:20 UTC	Run