Get rid of harmful each loop over uploads to update. Instead we put all the unique access control posts for the uploads into a map for fast access (vs using the slow .find through array) and look up the post when it is needed when looping through the uploads in batches.
On a Discourse instance with ~93k uploads, a simplified version of the old method takes > 1 minute, and a simplified version of the new method takes ~18s and uses a lot less memory.
Martin Brennan
6f978bc95c