Destructive protection

Blocked operations

These operations are blocked by default and require --allow-destructive:

• drop_table — dropping entire tables
• drop_column — dropping columns
• drop_index — dropping indexes
• drop_foreign_key — dropping foreign key constraints
• drop_check — dropping check constraints
• drop_unique_constraint — dropping unique constraints
• drop_view — dropping views
• drop_materialized_view — dropping materialized views
• drop_extension — dropping extensions
• disable_rls — disabling row-level security
• drop_policy — dropping RLS policies
• drop_trigger — dropping triggers
• Column type narrowing (e.g., text -> varchar(50))
• Enum value removal (remove_enum_value)

Behavior

When a blocked operation is encountered:

1. It is reported as “blocked” in the plan output
2. The rest of the migration proceeds normally
3. No data is lost

# See what would be blocked
npx @smplcty/schema-flow plan

# Allow destructive operations
npx @smplcty/schema-flow run --allow-destructive

Advisory locking

Before running migrations, schema-flow acquires a PostgreSQL advisory lock. This prevents concurrent migration processes from conflicting. The lock is released after migration completes or on error.

Transactional execution

DDL runs within transactions. If any statement fails, the entire transaction rolls back. No partial migrations.

Timeouts

Setting	Default	Purpose
Lock timeout	5000ms	Prevents blocking other queries while waiting for table locks
Statement timeout	30000ms	Prevents long-running DDL from holding locks indefinitely

Automatic retry

Transient errors are retried up to 3 times with exponential backoff:

Error code	Meaning
55P03	Lock timeout
57014	Statement timeout / query cancellation
40001	Serialization failure
40P01	Deadlock detected

Interrupted migrations

If a migration is interrupted:

• Re-running picks up where it left off (file hash tracking)
• Transactional phases either fully commit or fully roll back
• Failed CONCURRENTLY operations leave invalid indexes that can be detected and retried