USD File Size Not Reducing After Deleting Assets in Isaac Sim

Omniverse Isaac Sim
1

Isaac Sim Version

5.1.0
5.0.0

Operating System

Ubuntu 22.04

GPU Information

  • Model: RTX A 6000
  • Driver Version:580

Topic Description

USD File Size Does Not Reduce After Deleting Assets in Isaac Sim (Only “Save As” Shrinks File)

Detailed Description

Hi everyone,

I’m observing some unexpected behavior regarding USD file size management in Isaac Sim and wanted to check if others have noticed the same or can explain the intended behaviour

Scenario:

  1. I load a USD asset that includes physics properties, with an initial file size of approximately 30 MB.

  2. I create 5 duplicates of this asset in the scene. After saving the scene, the resulting USD file size becomes approximately 130 MB.

  3. I then delete 3 of the duplicated models from the scene and save the file. However, the file size remains ~130 MB, whereas I expected it to reduce proportionally.

  4. Even after deleting all assets from the scene and saving, the file size still stays at ~130 MB.

  5. If I instead use “Save As” after deleting 3 assets, the file size reduces as expected (to around 50 MB).
    Similarly, using “Save As” after deleting everything results in a file size of only ~4 KB
    Questions    :

  • Is this behavior expected due to how USD layers, references, or cached data are handled?
  • Why doesn’t a normal “Save” remove unused data, while “Save As” does?
  • Are there recommended best practices or tools in Isaac Sim / Omniverse to clean up or compact USD files without relying on “Save As” every time?

Screenshots or Videos

image
image971×234 18 KB

Photo with 5 assets. File size is 134 MB

image
image934×169 14.4 KB

Photo after doing “Save as”. File size has been reduced to 33.75 MB

3

Hello,

This is a USD format limitation, not an Isaac Sim bug. The team is aware and monitoring community discussions for potential improvements.
It stems from how USD binary files (.usdc) store data (USD binary files use an append-only structure).
The USD community is discussing better approaches for file compaction. See: Binary SDF file size doe not decrease on content removal - #2 by mtucker - USD - Alliance for OpenUSD

As noted in the AOUSD forum: “The save-to-another-file-then-move is the right way to do this when you have decided that the time cost of writing the complete file is worth it for the amount of disk space you’ll be saving.”

There’s also an alternative: according to USD Terms and Concepts — Universal Scene Description 25.11 documentation , you can use usdcat command-line tool which rewrites the file in its most compact form.

1 Like
4

Thnaks for the response. Then until there is an official update on the USD resizing, I hope we can continue proceed with “Save as” option to shorten the file size.
Also, how will we be informed when there is an official update on this?