Schema Evolution

Production databases change. Columns get added, renamed, or dropped. Schema Evolution is Zwiron’s system for detecting these changes and giving you control over how they are applied to the destination.

How it works

Every time a pipeline runs, Zwiron compares the current source schema (columns and types) to the schema it last saw. If anything changed, it creates a Schema Proposal — a record of exactly what changed and whether it’s safe to apply automatically. You review and act on proposals from the job detail page → Schema tab.

Types of changes

Change type	Description	Auto-safe?
`add_column`	A new column appeared at the source	✅ Yes — adds the column at the destination
`drop_column`	A column was removed from the source	⚠️ No — needs your review
`modify_column`	A column’s type changed	⚠️ Depends — widening is safe, narrowing is not

Safe vs. unsafe changes

Safe (auto-applicable)

Zwiron can apply these automatically without risk of data loss:

Adding a new column
Widening a column type (e.g. int32 → int64, varchar(50) → varchar(255))

Unsafe (require your review)

These require a human decision because they can cause data loss or breaks:

Dropping a column — the destination keeps the column with NULLs, or you can approve dropping it
Narrowing a type — e.g. int64 → int32 may truncate values
Modifying a primary key column — could break upsert logic

Proposal statuses

Status	Meaning
Pending	Change detected, waiting for your review
Applied	You approved — change was applied to the destination
Rejected	You rejected — change is ignored, pipeline continues as-is
Resynced	You triggered a full re-sync for this table after the schema change
Auto-applied	Zwiron applied the change automatically (safe changes only)

Reviewing a proposal

Go to Jobs → select a job
Click the Schema tab
Review the pending proposal — you’ll see the old schema, the new schema, and each specific change
Choose an action:
- Apply — alter the destination table and resume syncing with the new schema
- Reject — ignore the change and continue syncing with the old schema
- Re-sync — drop and reload the full table with the new schema

Automatic application

By default, Zwiron auto-applies safe changes (new columns, widening) immediately without creating a pending proposal. You’ll see these in the proposal list with status auto_applied. Unsafe changes always require manual review.

Notifications

When a schema proposal is created and needs your review, Zwiron sends a notification. Configure in-app/email under Notifications (schema_pending_review / schema.proposal) or push to Slack/HTTP via Webhooks. When a safe change is auto-applied, you receive a schema_auto_applied notification.