multithreaded post file fingerprint creation

app/lib/tasks/create_post_file_fingerprints_task.rb

@@ -48,26 +48,46 @@ module Tasks
     def run_post_file_descending(start_at)
       last_post_file_id = get_progress(start_at)&.to_i
 
-      query = Domain::PostFile.where(state: "ok").includes(:blob, :thumbnails)
+      query = Domain::PostFile.where(state: "ok")
       query = query.where(id: ..last_post_file_id) if last_post_file_id
 
       log("counting post files to process...")
       # total = 49_783_962 # cache this value
       total = query.count
       pb = create_progress_bar(total)
+      batch_size = 16
+      num_threads = 6
+      mutex = Mutex.new
 
-      query.find_each(
+      query.find_in_batches(
         order: :desc,
-        batch_size: 32,
+        batch_size: batch_size * num_threads,
         start: last_post_file_id,
-      ) do |post_file|
+      ) do |post_files|
+        break if interrupted?
+        last_post_file = T.must(post_files.last)
+
+        post_files
+          .each_slice(post_files.size / num_threads)
+          .map
+          .with_index do |batch, index|
+            Thread.new do
+              batch.each do |post_file|
+                break if interrupted?
+                migrate_post_file(post_file)
+              ensure
+                mutex.synchronize do
+                  pb.progress = [pb.progress + 1, pb.total].min
+                end
+              end
+            end
+          end
+          .map(&:join)
+
         break if interrupted?
 
-        migrate_post_file(post_file)
-        pb.progress = [pb.progress + 1, pb.total].min
-
-        if pb.progress % 100 == 0
-          post = post_file.post
+        if pb.progress % 128 == 0
+          post = last_post_file.post
           creator_str =
             if post&.class&.has_creators?
               T.unsafe(post).creator&.to_param || "(none)"
@@ -75,15 +95,15 @@ module Tasks
               "(none)"
             end
           post_desc =
-            "#{creator_str&.rjust(20)} / #{post_file.post&.to_param}".ljust(40)
+            "#{creator_str&.rjust(20)} / #{last_post_file.post&.to_param}".ljust(
+              40,
+            )
           log(
-            "post_file = #{post_file.id} :: #{post_desc} - #{post_file.post&.title_for_view}",
+            "post_file = #{last_post_file.id} :: #{post_desc} - #{last_post_file.post&.title_for_view}",
           )
-          last_post_file_id = T.must(post_file.id)
+          last_post_file_id = T.must(last_post_file.id)
           save_progress(last_post_file_id.to_s)
         end
-
-        break if interrupted?
       end
 
       save_progress(last_post_file_id.to_s) if last_post_file_id