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pgmold

Safety Rules

Destructive operation blocking

Section titled “Destructive operation blocking”

By default, pgmold blocks destructive operations:

  • DROP TABLE, DROP COLUMN, DROP ENUM require --allow-destructive
  • Type narrowing and SET NOT NULL produce warnings
Terminal window
# This will fail if the plan includes any drops
pgmold apply -s sql:schema.sql -d postgres://localhost/mydb


# Explicitly opt in to destructive operations
pgmold apply -s sql:schema.sql -d postgres://localhost/mydb --allow-destructive

Production mode

Section titled “Production mode”

Set PGMOLD_PROD=1 for production mode, which blocks table drops entirely — even with --allow-destructive.

Terminal window
PGMOLD_PROD=1 pgmold apply -s sql:schema.sql -d postgres://localhost/prod

Lock hazard warnings

Section titled “Lock hazard warnings”

pgmold warns about operations that acquire heavy locks, such as:

  • Adding a column with a default value (rewrites the table in older PostgreSQL versions)
  • Adding a NOT NULL constraint without a default
  • Creating an index without CONCURRENTLY

These warnings help prevent downtime during migrations on large tables.