ProcessWire runtime page cache: safe boundary for $pages->uncache() when other loaded pages reference the target

Answer

Yes – calling $pages->uncache($page) on a page that other loaded pages still reference is safe from a cache‑consistency viewpoint. The method only removes the entry from ProcessWire’s internal runtime cache; any existing PHP variables that hold a reference to that Page object continue to point to the same instance, so the object is not destroyed and its property values remain unchanged.

What happens on next access

If later code executes $pages->get($id) or a find that matches the same ID, ProcessWire loads a fresh Page instance from the database, stores it in the cache, and returns that new object. The old instance that your variables still reference is not updated, so it may contain stale data unless you re‑fetch the page.

Confirmed facts from the source

• Uncache removes the cache entry but does not destroy the Page object while PHP references exist.
• A subsequent get/find returns a new instance; old references stay stale.
• If other loaded pages keep the uncached page as a parent, page‑reference field value, or child, those references keep the object alive, so uncache() alone does not reduce memory contributed by that object.
• $pages->uncacheAll() clears the whole cache array, yet any Page objects still referenced elsewhere remain in memory.

Steps to bound memory in your import loop

1. After you have finished using a loaded $page, call $pages->uncache($page) to drop the cache entry.
2. Immediately unset any PHP variables that hold the page (e.g., unset($page)) or avoid storing it in arrays.
3. If you have cleared all references to processed pages, you may call $pages->uncacheAll() periodically (e.g., every 500 iterations) to ensure the internal cache does not grow.
4. Prefer selector pagination with a limit (and optionally offset) so that only a bounded number of pages are loaded at any time.

Missing diagnostic detail

Do you retain any references to the processed pages after calling $pages->uncache() (for example, in an array, passed to a function, or stored in a property)? If yes, the memory will not drop until those references are unset; confirming this will determine whether additional uncacheAll() calls are needed.