public Builder mergeTaskTtl(com.google.protobuf.Duration value) {
      if (taskTtlBuilder_ == null) {
        if (((bitField0_ & 0x00000100) != 0)
            && taskTtl_ != null
            && taskTtl_ != com.google.protobuf.Duration.getDefaultInstance()) {
          getTaskTtlBuilder().mergeFrom(value);
        } else {
          taskTtl_ = value;
        }
      } else {
        taskTtlBuilder_.mergeFrom(value);
      }
      if (taskTtl_ != null) {
        bitField0_ |= 0x00000100;
        onChanged();
      }
      return this;
    }
<pre>
The maximum amount of time that a task will be retained in
this queue.

Queues created by Cloud Tasks have a default `task_ttl` of 31 days.
After a task has lived for `task_ttl`, the task will be deleted
regardless of whether it was dispatched or not.

The `task_ttl` for queues created via queue.yaml/xml is equal to the
maximum duration because there is a
[storage quota](https://cloud.google.com/appengine/quotas#Task_Queue) for
these queues. To view the maximum valid duration, see the documentation for
[Duration][google.protobuf.Duration].
</pre>

<code>.google.protobuf.Duration task_ttl = 9;</code>
java-tasks/proto-google-cloud-tasks-v2beta2/src/main/java/com/google/cloud/tasks/v2beta2/Queue.java