Getting Materializer.settings.maxFixedBufferSize

Upgrading Play framework version, which led to an Akka upgrade, which deprecated Materializer.settings, with a reference to “Use attributes to access settings from stages”. The attribute i need to read (not write) is maxFixedBufferSize.

I have access to the materializer, but not that much else (I don’t really know what “stages” are).

I was getting it by just doing materializer.settings.maxFixedBufferSize, but I’m concerned that will go away soon.

Question: How do I read that value in a non-deprecated way?

The reason I need it is that I need make sure we don’t drop any actor messages even under load, so I need an effectively unbounded buffer, but maxFixedBufferSize is typically very large (1000000000 by default it seems), so when Buffers.scala contains:

private[akka] object Buffer {
  val FixedQueueSize = 128
  val FixedQueueMask = 127

  def apply[T](size: Int, effectiveAttributes: Attributes): Buffer[T] =
    apply(size, effectiveAttributes.mandatoryAttribute[ActorAttributes.MaxFixedBufferSize].size)

  def apply[T](size: Int, max: Int): Buffer[T] =
    if (size < FixedQueueSize || size < max) FixedSizeBuffer(size)
    else new BoundedBuffer(size)

Then the line if (size < FixedQueueSize || size < max) FixedSizeBuffer(size) becomes very dangerous - whatever reasonable size I specify I’ll allocate a FixedSizeBuffer of that length. That’s quite undesirable, as most of the time, most of my buffers will only need to store 1-2 messages.

So the only way to get what I actually want, i.e. a BoundedBuffer (which has the sensible strategy of using a small fixed array and then switching to a dynamic queue as needed), is to pass in a size of maxFixedBufferSize.


It would be nice to be able to get a BoundedBuffer with a smaller capacity than 1,000,000,000, so being able to adjust the default value for my materializer and setting it to a know value is another approach.

After some digging I found the configuration option which I can specify in my Play application.conf-file.

So that solves both problems.