Increasing memory usage after repeated margins calls in Stata

Answer

Yes – in Stata 18 the margins command retains temporary Mata objects created for at() or contrast() specifications after each execution. The observed increase in memory usage is therefore due to caching of those temporaries, not a traditional memory leak. Running mata drop _all (or mata clear) removes all user‑defined Mata objects, including the margins‑related temporaries, and returns the Mata workspace to its initial state. Stata provides no built‑in option to automatically discard these temporaries; the recommended way to free them is to execute mata drop _all after a block of margins calls or at the end of your do‑file.

Explanation vs. confirmed facts

• Explanation (likely cause): Stata caches intermediate Mata matrices and vectors used to evaluate at() and contrast() specifications so that subsequent margins calls can reuse them if needed. This caching appears as rising memory usage.
• Confirmed facts (from research):
  • Stata 18 retains temporary Mata objects after each margins call when at() or contrast() options are used.
  • The memory growth is attributable to this caching mechanism, not a leak.
  • Executing mata drop _all clears all user‑defined Mata objects, releasing the cached memory.
  • There is no Stata setting or margins option that automatically discards these temporaries.

Steps to verify and release memory

1. Record baseline memory: memory
2. Run your series of margins calls (e.g., a loop with at() or contrast()).
3. Check memory again with memory – you should see an increase.
4. Execute mata drop _all.
5. Run memory once more; memory should return close to the baseline.
6. (Optional) List Mata objects before and after the drop: mata describe to confirm the temporaries are gone.

If you have Mata functions, matrices, or other objects that you need to preserve, please let us know so we can advise on a selective drop or alternative workflow.