mongodb/node-mongodb-native · error · MongoInvalidArgumentError

Cannot request unacknowledged write concern and verbose…

Error message

Cannot request unacknowledged write concern and verbose results

What it means

Thrown when bulk write options request writeConcern w:0 (unacknowledged) together with verboseResults: true. Unacknowledged writes do not return per-operation results, so requesting verbose detail is contradictory and the driver rejects it up front rather than silently dropping data.

Solutions

If you need verbose results, use an acknowledged write concern (omit w:0 or set w:1/majority).
If you need fire-and-forget throughput, drop verboseResults: false (or omit it).
Audit writeConcern inheritance — connection-string w=0 propagates to all bulkWrite calls unless overridden.

Example fix

// before
await client.bulkWrite(models, {
  writeConcern: { w: 0 },
  verboseResults: true
});

// after
await client.bulkWrite(models, {
  writeConcern: { w: 1 },
  verboseResults: true
});

Defensive patterns

Strategy: validation

Validate before calling

if (options?.writeConcern?.w === 0 && options?.verboseResults) {
  throw new Error('Cannot combine w:0 with verboseResults');
}
await client.bulkWrite(models, options);

Prevention

Treat w:0 as fire-and-forget — never pair it with options that expect results.
Document the writeConcern contract for any global default you set.

When it happens

Trigger: Calling client.bulkWrite(models, { writeConcern: { w: 0 }, verboseResults: true }). Also when w:0 is inherited from the connection string or client options and verboseResults is explicitly enabled on the call.

Common situations: Performance tuning that sets w:0 globally and then turns on verboseResults for debugging; copy-pasting options between calls without reconciling them.

Related errors

AI-assisted analysis of mongodb/node-mongodb-native@dce7939f86 (2026-08-11). Data as JSON: /api/errors/69fb5d3348057d0b. Report an issue: GitHub.

Appendix: source

Thrown at src/operations/client_bulk_write/executor.ts:64

    }

    this.client = client;
    this.operations = operations;
    this.options = {
      ordered: true,
      bypassDocumentValidation: false,
      verboseResults: false,
      ...options
    };

    // If no write concern was provided, we inherit one from the client.
    if (!this.options.writeConcern) {
      this.options.writeConcern = WriteConcern.fromOptions(this.client.s.options);
    }

    if (this.options.writeConcern?.w === 0) {
      if (this.options.verboseResults) {
        throw new MongoInvalidArgumentError(
          'Cannot request unacknowledged write concern and verbose results'
        );
      }

      if (this.options.ordered) {
        throw new MongoInvalidArgumentError(
          'Cannot request unacknowledged write concern and ordered writes'
        );
      }
    }
  }

  /**
   * Execute the client bulk write. Will split commands into batches and exhaust the cursors
   * for each, then merge the results into one.
   * @returns The result.
   */
  async execute(): Promise<ClientBulkWriteResult> {

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