From 3a7bf8101ad059998ac8499bb0770b0a2b481501 Mon Sep 17 00:00:00 2001
From: Donal McBreen <donal@basecamp.com>
Date: Tue, 26 Sep 2023 14:05:32 +0100
Subject: [PATCH] Rework expiry

---
 app/models/solid_cache/entry.rb   |  4 ++--
 lib/solid_cache/cluster/expiry.rb | 29 ++++++++++++-----------------
 2 files changed, 14 insertions(+), 19 deletions(-)

diff --git a/app/models/solid_cache/entry.rb b/app/models/solid_cache/entry.rb
index 0d86360..3b659c0 100644
--- a/app/models/solid_cache/entry.rb
+++ b/app/models/solid_cache/entry.rb
@@ -64,9 +64,9 @@ def id_range
         end
       end
 
-      def first_n(n)
+      def first_n_id_and_created_at(n)
         uncached do
-          order(:id).limit(n)
+          order(:id).limit(n).pluck(:id, :created_at)
         end
       end
 
diff --git a/lib/solid_cache/cluster/expiry.rb b/lib/solid_cache/cluster/expiry.rb
index 6a95b1a..52bef25 100644
--- a/lib/solid_cache/cluster/expiry.rb
+++ b/lib/solid_cache/cluster/expiry.rb
@@ -12,11 +12,12 @@ module Expiry
       # might be deleted already. The expiry multiplier should compensate for that.
       EXPIRY_SELECT_MULTIPLIER = 3
 
-      attr_reader :expiry_batch_size, :expire_every, :max_age, :max_entries
+      attr_reader :expiry_batch_size, :expiry_select_size, :expire_every, :max_age, :max_entries
 
       def initialize(options = {})
         super(options)
         @expiry_batch_size = options.fetch(:expiry_batch_size, 100)
+        @expiry_select_size = expiry_batch_size * EXPIRY_SELECT_MULTIPLIER
         @expire_every = [(expiry_batch_size / EXPIRY_MULTIPLIER).floor, 1].max
         @max_age = options.fetch(:max_age, 2.weeks.to_i)
         @max_entries = options.fetch(:max_entries, nil)
@@ -32,30 +33,24 @@ def cache_full?
         end
 
         def expire_later
-          async { expire_batch }
+          async { expire }
         end
 
-        def expire_batch
+        def expire
           Entry.expire(expiry_candidate_ids)
         end
 
-        def expiry_counter
-          @expiry_counters ||= connection_names.to_h { |connection_name| [ connection_name, Counter.new(expire_every) ] }
-          @expiry_counters[Entry.current_shard]
-        end
-
-        def expiry_select_size
-          expiry_batch_size * EXPIRY_SELECT_MULTIPLIER
-        end
-
         def expiry_candidate_ids
-          cache_full = cache_full?
-
           Entry \
-            .first_n(expiry_select_size)
-            .pluck(:id, :created_at)
-            .filter_map { |id, created_at| id if cache_full || created_at < max_age.seconds.ago }
+            .first_n_id_and_created_at(expiry_select_size)
+            .tap { |candidates| candidates.select! { |id, created_at| created_at < max_age.seconds.ago } unless cache_full? }
             .sample(expiry_batch_size)
+            .map { |id, created_at| id }
+        end
+
+        def expiry_counter
+          @expiry_counters ||= connection_names.to_h { |connection_name| [ connection_name, Counter.new(expire_every) ] }
+          @expiry_counters[Entry.current_shard]
         end
 
         class Counter