What causes "Error while processing the element" in apache/beam?

Inspect records emitted on the error output PCollection to identify the serialization failure.

Error while processing the element

Error message

Error while processing the element

What it means

TFRecordWriteSchemaTransformProvider's DoFn converts each input Row to bytes via toBytesFn before writing. If the conversion throws and error handling is enabled, the failure is logged at WARN and the element is emitted to the ERROR_TAG as an ErrorHandling record; if error handling is disabled, the exception becomes a RuntimeException that fails the pipeline.

Solutions

Inspect records emitted on the error output PCollection to identify the serialization failure.
Validate/normalize the Row schema before writing so it matches the toBytesFn expectation.
Enable error handling (withErrorHandling) to divert bad rows instead of failing the bundle.
Fix the upstream transform producing non-conforming Rows.

Example fix

// before (no error output configured)
.write() // throws on serialization failure
// after
.withErrorHandling()  // routes serialization failures to the error output

Defensive patterns

Strategy: try-catch

Validate before calling

// Verify a sample Row serializes before writing
byte[] bytes = toBytesFn.apply(sampleRow);
if (bytes == null || bytes.length == 0) {
  throw new IllegalStateException("toBytesFn produced empty output for sample row");
}

Try / catch

try {
  byte[] out = toBytesFn.apply(row);
} catch (Exception e) {
  errorOutput.emit(ErrorHandling.errorRecord(errorSchema, row, e));
}

Prevention

Validate the Row schema matches the serialization target before the write transform.
Reject or null-check fields that cannot be encoded (e.g. nulls in required proto fields) upstream.
Enable error handling when writing user-derived data.
Test toBytesFn against representative rows in unit tests.

When it happens

Trigger: Writing Rows to TFRecord files when toBytesFn throws on an element (null required field, incompatible type, serialization failure) — logged and routed to error output when handleErrors is true, rethrown as RuntimeException otherwise.

Common situations: Row schema not matching the expected serialization format (e.g. proto mismatch); nulls in non-nullable proto fields; rows produced upstream with the wrong schema.

Related errors

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/ea97208edcc74aa1. Report an issue: GitHub.

Appendix: source

Thrown at sdks/java/core/src/main/java/org/apache/beam/sdk/io/TFRecordWriteSchemaTransformProvider.java:233

        Schema errorSchema,
        boolean handleErrors) {
      this.toBytesFn = toBytesFn;
      this.errorCounter = Metrics.counter(TFRecordReadSchemaTransformProvider.class, name);
      this.handleErrors = handleErrors;
      this.errorSchema = errorSchema;
    }

    @ProcessElement
    public void process(@DoFn.Element Row row, MultiOutputReceiver receiver) {
      byte[] output = null;
      try {
        output = toBytesFn.apply(row);
      } catch (Exception e) {
        if (!handleErrors) {
          throw new RuntimeException(e);
        }
        errorsInBundle += 1;
        LOG.warn("Error while processing the element", e);
        receiver.get(ERROR_TAG).output(ErrorHandling.errorRecord(errorSchema, row, e));
      }
      if (output != null) {
        receiver.get(OUTPUT_TAG).output(output);
      }
    }

    @FinishBundle
    public void finish() {
      errorCounter.inc(errorsInBundle);
      errorsInBundle = 0L;
    }
  }
}

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