Warning Num Samples Per Thread Reduced To 32768 Rendering Might Be Slower -

The "num_samples_per_thread reduced to 32768" warning is ultimately a sign that your render settings are working against your hardware. By lowering your raw sample counts, turning on Adaptive Sampling, and letting built-in AI denoisers handle the residual grain, you will bypass this hardware limitation entirely and finish your renders in a fraction of the time.

Reducing to 32768 is a "safe" fallback that typically works on most GPUs with at least 2–4 GB of VRAM, even if the original request was much larger. However, the overhead of managing twice as many batches (compared to 65536) can lead to a performance loss of anywhere from , depending on scene complexity and hardware.

Convert heavy geometry to proxies.

Total memory = (num_samples_per_thread) × (bytes per sample state) × (num_threads)

It starts like a tiny whisper from the engine: a single line of text in a console, a fleeting warning on startup. You glance at it, half-curious, half-annoyed. “num samples per thread reduced to 32768 — rendering might be slower.” Technical, terse, and strangely human: an engine telling you it’s doing its best with less to work with. However, the overhead of managing twice as many

When you initiate a GPU or hybrid (CUDA/RTX) render, V-Ray attempts to load all scene assets—including geometry, high-resolution textures, lighting caches, and frame buffers—directly into your graphics card's physical memory.

When you increase num_samples_per_thread , you are effectively asking the renderer to allocate a larger per thread. The total memory required is roughly: You glance at it, half-curious, half-annoyed

To fix the slowdown, you must reduce the memory footprint of your scene using the following optimizations :

To maximize speed, the engine allocates a high number of samples to each concurrent processing thread. However, when VRAM usage hits its ceiling, V-Ray dynamically reduces the to a bare minimum threshold—frequently exactly 32,768 . This allows the render to crawl across the finish line rather than failing instantly, but it often results in rendering speeds that are 10 to 20 times slower. Core Causes of VRAM Exhaustion When you increase num_samples_per_thread

. To prevent an outright software crash or an Out-of-Memory (OOM) failure, the rendering engine automatically downscales its workload per computing thread to fit within your graphics card's hardware limits. While this safety feature keeps your machine from crashing, it drastically chokes processing efficiency and causes render times to skyrocket.