# Performance & Memory Character Creator characters are detailed, and detailed characters use memory. Here's where the cost comes from and how to keep your sessions fast and lean. ## The fastest fix: import as USD **USD import mode** sidesteps almost all of this cost, and it's the default. Character Creator's USD export keeps the facial blendshapes sparse, and the tool keeps them sparse **all the way through deformation**, so a heavy HD character imports in **about a second** and a loaded character stays under 8 GB, where the same character costs 20–40 GB via FBX. If performance or memory is a concern, exporting and importing as **USD is the single biggest thing you can do**. See [USD vs FBX](../getting-started/import-modes.md). The one trade-off: because the sparse path recomputes the facial deformation each frame instead of holding gigabytes of pre-expanded data, scrubbing a very heavy HD character is somewhat slower per frame. On standard characters you won't notice. The rest of this page applies mainly to **FBX import**, which still has to expand the character on load (and which you'd use for FBX-only features like wrinkles). One thing USD does **not** change is playback memory over long frame ranges. See [Long animations and playback memory](#long-animations-and-playback-memory) below. ## Why the first FBX build is slow When you import an FBX character, the slow part is Houdini loading and expanding it, particularly its blendshapes (the facial expression targets). A fully-featured CC character has many of these, and expanding them is memory- and time-intensive. This is inherent to how Houdini handles FBX character data, not something specific to this tool. (USD import avoids it, as above.) The good news: this cost is paid **once**, at build time. After that, adjusting your look on the controller is fast, because the materials just reference the controller. They don't re-cook the character. !!!info Expect a heavy or HD character imported **via FBX** to use a substantial amount of RAM once loaded. This is normal for film-quality character data in Houdini. Lighter characters are correspondingly cheaper, and USD import is cheaper across the board. !!! ## Keeping look-dev fast While you're working on the look, use these to stay responsive: * **Quality ▸ Preview** turns off subsurface scattering and uses cheap eyes. It is the single biggest speed-up. (See [The Lookdev Controller](../lookdev/lookdev-controller.md).) * **Displacement ▸ Disable or Bump**: true displacement is expensive, so use it only for final renders. * **Hero Eyes off**, for any character whose eyes aren't the focus. Switch all of these to full quality only when you're ready for final renders. ## Managing memory ### Long animations and playback memory This one applies to **both USD and FBX**, and is separate from import cost. Once a character is animated, Houdini caches the **deformed mesh for every frame you play or scrub** so playback stays smooth. For a heavy or HD character that's roughly **20 MB per frame**, so a several-hundred-frame range can add **10–20 GB** on top of the character itself, and it grows the more of the range you touch. USD does **not** avoid this: the per-frame deformed mesh is the same size whichever way you imported, so playing a long animation fills the cache the same. The difference is the baseline it stacks on. In USD mode the character itself only costs a few gigabytes, so even with a full playback cache you stay far below FBX-mode totals. To keep it under control: * **Lower Houdini's geometry cache limit** in *Edit ▸ Preferences ▸ Cache*, "Cache Memory (MB)". This is a hard ceiling on exactly this memory; a smaller value trades some scrub smoothness for a lower RAM cap. * **Play only the range you need.** The cache fills in proportion to the frames you actually visit, so set your playback range to the shot, not the whole clip. * **Clear Scene Cache** (below) after you're done scrubbing a heavy range. ### Clear Scene Cache The **Clear Scene Cache** button (in the **Utilities** tab of the Reallusion Rigger node) unloads cached geometry from Houdini's caches to reclaim memory. It is useful after deleting characters or removing animation clips. ![](../static/clear-scene-cache-button.png) !!!warning Geometry that's currently displayed won't unload Houdini keeps actively-displayed data resident by design. Clear Scene Cache reclaims cooked data that's no longer needed (from deleted characters or removed animations), not the character you're currently looking at. To free a loaded character's memory, delete or bypass its nodes first, then clear the cache. !!! ## Stash Rig: reopening in seconds The Rigger has no skin cache. Instead, **Stash Rig** (on by default, in **Character ▸ Build** and on the rig node's **Rig Settings**) stores the built and baked rig, so a reopened scene loads in seconds instead of rebuilding and rebaking it. On a standard FBX character that is about 3 seconds instead of nearly a minute. It costs hip size: about 220 MB for a standard character, more for a heavy HD one, plus each baked clip. Setting **Stash In** to **External File** and pressing **Save to Disk** keeps the hip small, a few MB, by writing the rig to a file beside it. See [Rig Settings](../using/rig-settings.md). With Stash Rig off, changing the scene's frame range rebuilds and rebakes the whole rig, which takes about as long as the first build. See [Building the Rig](../using/building-the-rig.md). ## Multiple characters You can have several characters in one scene. Each gets its own stem-prefixed nodes, its own lookdev controller and its own rig node, so they don't interfere with each other. Just be mindful that each one carries its own memory cost. On a memory-constrained machine, work with one character at a time.