@java.lang.Override
  public void writeTo(com.google.protobuf.CodedOutputStream output) throws java.io.IOException {
    if (((bitField0_ & 0x00000001) != 0)) {
      output.writeMessage(1, getStackFrames());
    }
    if (stackTraceHashId_ != 0L) {
      output.writeInt64(2, stackTraceHashId_);
    }
    getUnknownFields().writeTo(output);
  }
<pre>
The hash ID is used to conserve network bandwidth for duplicate
stack traces within a single trace.

Often multiple spans will have identical stack traces.
The first occurrence of a stack trace should contain both the
`stackFrame` content and a value in `stackTraceHashId`.

Subsequent spans within the same request can refer
to that stack trace by only setting `stackTraceHashId`.
</pre>

<code>int64 stack_trace_hash_id = 2;</code>

@return The stackTraceHashId.
java-trace/proto-google-cloud-trace-v2/src/main/java/com/google/devtools/cloudtrace/v2/StackTrace.java