dgraph-io/dgraph · error

while dumping table %s

Error message

while dumping table %s

What it means

dumpTables first phase calls dumpTable for every table in m.tableInfos, which reads all SQL rows and emits RDF data to the data writer. If any per-table dump fails (SQL query error, scan error, getValue error), it is wrapped with "while dumping table <name>" so the offending table is identified.

Source

Thrown at dgraph/cmd/migrate/dump.go:74

		tableInfo := m.tableInfos[table]
		for _, index := range createDgraphSchema(tableInfo) {
			_, err := m.schemaWriter.WriteString(index)
			if err != nil {
				return errors.Wrapf(err, "while writing schema")
			}
		}
	}
	return m.schemaWriter.Flush()
}

// dumpTables goes through all the tables twice. In the first time it generates RDF entries for the
// column values. In the second time, it follows the foreign key constraints in SQL tables, and
// generate the corresponding Dgraph edges.
func (m *dumpMeta) dumpTables() error {
	for table := range m.tableInfos {
		fmt.Printf("Dumping table %s\n", table)
		if err := m.dumpTable(table); err != nil {
			return errors.Wrapf(err, "while dumping table %s", table)
		}
	}

	for table := range m.tableInfos {
		fmt.Printf("Dumping table constraints %s\n", table)
		if err := m.dumpTableConstraints(table); err != nil {
			return errors.Wrapf(err, "while dumping table %s", table)
		}
	}

	return m.dataWriter.Flush()
}

// dumpTable converts the cells in a SQL table into RDF entries,
// and sends entries to the m.dataWriter
func (m *dumpMeta) dumpTable(table string) error {
	tableGuide := m.tableGuides[table]
	tableInfo := m.tableInfos[table]

View on GitHub (pinned to 759e242be6)

Solutions

1. Identify the table name embedded in the wrapped message and run a manual SELECT on it to find the bad rows.
2. Fix NULL/invalid values in that table (or preprocess with COALESCE) before migrating.
3. Verify DB connectivity and grants for the migrate user on that table.
4. Rerun migrate; since it is a full dump, restart after fixing the data source.

Example fix

// before
SELECT * FROM orders; -- row with NULL cust_id crashes dumpTable
// after
SELECT id, COALESCE(cust_id, 0) AS cust_id, ... FROM orders; -- or clean NULLs before migrating

-- find problematic rows before migrating
SELECT COUNT(*) FROM orders WHERE cust_id IS NULL OR id IS NULL;

if err := migrate.Run(); err != nil {
	var tbl string
	if m := tableRe.FindStringSubmatch(err.Error()); m != nil {
		tbl = m[1] // parse table from "while dumping table X"
	}
	log.Printf("dump failed for table %s: %+v", tbl, err)
}

When it happens

Trigger: m.dumpTable(table) returns an error for any table: the SELECT of the table fails, rows.Next() hits an unexpected driver error, or a row cell fails conversion in getValue (nil value, invalid NullInt64/NullTime/NullFloat64).

Common situations: MySQL connection dropped mid-migration; a table contains NULLs the converter rejects; unsupported column type causes type assertion panic/error downstream; insufficient privileges to read a table.

Related errors

• while writing data file
• nil value found
• found invalid nullint
• found invalid nulltime
• while writing schema

AI-assisted analysis of dgraph-io/dgraph@759e242be6 (2026-09-01). Data as JSON: /api/errors/7844aea35e76f46f. Report an issue: GitHub.