PERF: Update `s3:expire_missing_assets` to delete in batches (#18908)

Some sites may have thousands of stale assets - deleting them one-by-one is very slow.

Followup to e8570b5cc9

lib/s3_helper.rb

@@ -105,6 +105,15 @@ class S3Helper
   rescue Aws::S3::Errors::NoSuchKey, Aws::S3::Errors::NotFound
   end
 
+  def delete_objects(keys)
+    s3_bucket.delete_objects({
+      delete: {
+        objects: keys.map { |k| { key: k } },
+        quiet: true,
+      },
+    })
+  end
+
   def copy(source, destination, options: {})
     if options[:apply_metadata_to_destination]
       options = options.except(:apply_metadata_to_destination).merge(metadata_directive: "REPLACE")

lib/tasks/s3.rake

@@ -204,6 +204,8 @@ end
 task 's3:expire_missing_assets' => :environment do
   ensure_s3_configured!
 
+  puts "Checking for stale S3 assets..."
+
   assets_to_delete = existing_assets.dup
 
   # Check that all current assets are uploaded, and remove them from the to_delete list
@@ -217,13 +219,20 @@ task 's3:expire_missing_assets' => :environment do
 
   if assets_to_delete.size > 0
     puts "Found #{assets_to_delete.size} assets to delete..."
+
     assets_to_delete.each do |to_delete|
       if !to_delete.start_with?(prefix_s3_path("assets/"))
         # Sanity check, this should never happen
         raise "Attempted to delete a non-/asset S3 path (#{to_delete}). Aborting"
       end
-      puts "Deleting #{to_delete}..."
-      helper.delete_object(to_delete)
+    end
+
+    assets_to_delete.each_slice(500) do |slice|
+      message = "Deleting #{slice.size} assets...\n"
+      message += slice.join("\n").indent(2)
+      puts message
+      helper.delete_objects(slice)
+      puts "... done"
     end
   else
     puts "No stale assets found"

spec/lib/s3_helper_spec.rb

@@ -212,4 +212,14 @@ RSpec.describe "S3Helper" do
       expect(s3_helper.ensure_cors!([S3CorsRulesets::BACKUP_DIRECT_UPLOAD])).to eq(false)
     end
   end
+
+  describe "#delete_objects" do
+    let(:s3_helper) { S3Helper.new("test-bucket", "", client: client) }
+
+    it "works" do
+      # The S3::Client with `stub_responses: true` includes validation of requests.
+      # If the request were invalid, this spec would raise an error
+      s3_helper.delete_objects(["object/one.txt", "object/two.txt"])
+    end
+  end
 end