Override samples and branched path tracing Branched Path Tracing provides AA samples and multiplier samples for different rays: diffuse, glossy, etc. So Total sampling for each ray is defined as AA*multiplier.

But what is renderlayer's Override samples in this case? Does it override AA samples only or Total sample number?
The Render Layer 'Override' setting overrides the AA samples.

For example, setting the render layer override to 300 while having Diffuse branched path tracing samples set to 5 will result in 1500 Diffuse samples.

One interesting point to note is how the override interacts with the Square Samples setting as it overrides before the squaring takes place - so setting Override to, say, 300 with Square Samples enabled will be equivalent to setting to 90000 without squaring enabled.