GraphQL DataLoader fails with 400 when batching many IDs

I'm running a GraphQL server using postgraphile and dataloader to batch and load data from a backend microservice. When the number of IDs passed to the loader grows large (~100+), the request fails with a 400 Bad Request error.

Here's the relevant code:

Data loader:

import DataLoader from "dataloader";
import { OptMetricsServiceApi } from "../integrations/OptMetricsService";

export const createDefaultAnalyticsLoader = (
  optMetricService: OptMetricsServiceApi
) =>
  new DataLoader(async (opportunityIds: Array<string>) => {
    const opportunityDefaultAnalytics =
      await optMetricService.getDefaultAnalyticForOpportunities({
        requestBody: opportunityIds,
      });
    return opportunityIds.map((id) =>
      opportunityDefaultAnalytics.find(
        ({ opportunityId }) => opportunityId === id
      )
    );
  });

And the resolver that uses it:

const loadReductionData = async (data: any, args: any, context: any) => {
  try {
    const defaultAnalytic: OpportunityAnalyticModel =
      await context.defaultAnalyticsLoader.load(data.runId);

    const reductionRawValue = getReductionRawValue(defaultAnalytic);
    return {
      reductionRawValue,
      ...defaultAnalytic,
    };
  } catch (error) {
    logger.warn(
      `Failed to load defaultAnalytic for ${
        data.runId
      }. Error: ${error}. Error Info: ${JSON.stringify(error)}`
    );
    return null;
  }
};

On many IDs(~100+) in the request, the request would fail with:

AxiosError: Request failed with status code 400

Versions:

dataloader: ^2.1.0
postgraphile: 4.12.9

Answer

We changed the backend API to accept the IDs in the POST body instead of as URL query params. Once that happened, the DataLoader worked correctly even with a large batch of IDs.