Question: It keeps jump :

```
Cached Files    292 ( 32.3 MBytes)

...

Cached Files 0 ( 0.0 Bytes)

```

Is that normal?

Why can't the figure be stable in production environment?

Answer: 
One possible reason for this could be that the cache is full. See this SO entry: [PHP APC: What happens when APC cache is full?](https://stackoverflow.com/questions/1053810/php-apc-what-happens-when-apc-cache-is-full)

Try setting to cache size to 64MB or 128MB and have a look how much of the cache is used. If it's over 32MB then you may have to increase the cache size permanently.
Use the apc.php script to see the use of the memory. You should keep 20% of free memory (after hours).

Use apc.shm\_size parameter to increase memory. Don't hesitate to give GB on large server.
If you cannot increase the segement size, increase the segment number.