What causes "conn: %v, db: %v" in golang-migrate/migrate?

Close the migrate instance once and let it own the connection lifecycle

conn: %v, db: %v

Error message

conn: %v, db: %v

What it means

In Firebird.Close, both the raw connection and sql.DB are closed; if either returns an error, the driver wraps both with fmt.Errorf("conn: %v, db: %v", ...). It reports that cleanup of the Firebird connection pool failed, possibly on both handles simultaneously. Note the wrapping discards error identity, so you must string-match to classify it.

Source

Thrown at database/firebird/firebird.go:104

	}

	px, err := WithInstance(db, &Config{
		MigrationsTable: purl.Query().Get("x-migrations-table"),
		DatabaseName:    purl.Path,
	})

	if err != nil {
		return nil, err
	}

	return px, nil
}

func (f *Firebird) Close() error {
	connErr := f.conn.Close()
	dbErr := f.db.Close()
	if connErr != nil || dbErr != nil {
		return fmt.Errorf("conn: %v, db: %v", connErr, dbErr)
	}
	return nil
}

func (f *Firebird) Lock() error {
	if !f.isLocked.CompareAndSwap(false, true) {
		return database.ErrLocked
	}
	return nil
}

func (f *Firebird) Unlock() error {
	if !f.isLocked.CompareAndSwap(true, false) {
		return database.ErrNotLocked
	}
	return nil
}

View on GitHub (pinned to 01a9643f14)

Solutions

Close the migrate instance once and let it own the connection lifecycle
Check network/DB availability and retry Close
Treat Close errors as non-fatal cleanup warnings if migration already succeeded
If you own the *sql.DB, close it only after migrate.Close() returns

Defensive patterns

Strategy: try-catch

Validate before calling

if sqlDB == nil || conn == nil {
    return fmt.Errorf("firebird handles already closed; skip migrate.Close")
}

Try / catch

if err := m.Close(); err != nil {
    // wrapped as "conn: %v, db: %v" — log and continue on shutdown
    log.Printf("firebird close (non-fatal): %v", err)
}

Prevention

Let migrate own the connection; do not close the *sql.DB separately
Call Close exactly once per migrate instance (use sync.Once in wrappers)
Treat Close errors during shutdown as warnings unless migrations are in flight

When it happens

Trigger: Calling migrate.Close() (which calls Firebird.Close) when the underlying sql.DB was already closed, the TCP connection to Firebird dropped, or the conn handle was closed elsewhere concurrently.

Common situations: Double-closing a migrate instance, network interruption before shutdown, closing the *sql.DB yourself before migrate.Close(), app shutdown with a stale Firebird connection.

Related errors

AI-assisted analysis of golang-migrate/migrate@01a9643f14 (2026-09-02). Data as JSON: /api/errors/e7de2ba3d0162fcd. Report an issue: GitHub.