Handle max_age: nil

README.md

@@ -80,7 +80,7 @@ Solid Cache supports these options in addition to the standard `ActiveSupport::C
 - `error_handler` - a Proc to call to handle any `ActiveRecord::ActiveRecordError`s that are raises (default: log errors as warnings)
 - `expiry_batch_size` - the batch size to use when deleting old records (default: `100`)
 - `expiry_method` - what expiry method to use `thread` or `job` (default: `thread`)
-- `max_age` - the maximum age of entries in the cache (default: `2.weeks.to_i`)
+- `max_age` - the maximum age of entries in the cache (default: `2.weeks.to_i`). Can be set to `nil`, but this is not recommended unless using `max_entries` to limit the size of the cache.
 - `max_entries` - the maximum number of entries allowed in the cache (default: `nil`, meaning no limit)
 - `cluster` - a Hash of options for the cache database cluster, e.g `{ shards: [:database1, :database2, :database3] }`
 - `clusters` - and Array of Hashes for multiple cache clusters (ignored if `:cluster` is set)

app/models/solid_cache/entry.rb

@@ -142,14 +142,26 @@ def to_binary(key)
 
         def expiry_candidate_ids(count, max_age:, max_entries:)
           cache_full = max_entries && max_entries < id_range
-          min_created_at = max_age.seconds.ago
+          return [] unless cache_full || max_age
+
+          # In the case of multiple concurrent expiry operations, it is desirable to
+          # reduce the overlap of entries being addressed by each. For that reason,
+          # retrieve more ids than are being expired, and use random
+          # sampling to reduce that number to the actual intended count.
+          retrieve_count = count * 3
 
           uncached do
-            order(:id)
-              .limit(count * 3)
-              .pluck(:id, :created_at)
-              .filter_map { |id, created_at| id if cache_full || created_at < min_created_at }
-              .sample(count)
+            candidates = order(:id).limit(retrieve_count)
+
+            candidate_ids = if cache_full
+              candidates.pluck(:id)
+            else
+              min_created_at = max_age.seconds.ago
+              candidates.pluck(:id, :created_at)
+                        .filter_map { |id, created_at| id if created_at < min_created_at }
+            end
+
+            candidate_ids.sample(count)
           end
         end
     end

test/unit/expiry_test.rb

@@ -36,7 +36,7 @@ class SolidCache::ExpiryTest < ActiveSupport::TestCase
     end
 
     test "expires records when the cache is full (#{expiry_method})" do
-      @cache = lookup_store(expiry_batch_size: 3, max_age: 2.weeks, max_entries: 2, expiry_method: expiry_method)
+      @cache = lookup_store(expiry_batch_size: 3, max_age: nil, max_entries: 2, expiry_method: expiry_method)
       default_shard_keys = shard_keys(@cache, :default)
       @cache.write(default_shard_keys[0], 1)
       @cache.write(default_shard_keys[1], 2)