diff --git a/lib/identity_cache.rb b/lib/identity_cache.rb
index a7407eaa..f575af3c 100644
--- a/lib/identity_cache.rb
+++ b/lib/identity_cache.rb
@@ -56,6 +56,7 @@ class InverseAssociationError < StandardError; end
   class UnsupportedScopeError < StandardError; end
   class UnsupportedAssociationError < StandardError; end
   class DerivedModelError < StandardError; end
+  class LockWaitTimeout < StandardError; end
 
   class << self
     include IdentityCache::CacheHash
@@ -116,10 +117,13 @@ def should_use_cache? # :nodoc:
     #
     # == Parameters
     # +key+ A cache key string
+    # +cache_fetcher_options+ A hash of options to pass to the cache backend
     #
-    def fetch(key)
+    def fetch(key, cache_fetcher_options = {})
       if should_use_cache?
-        unmap_cached_nil_for(cache.fetch(key) { map_cached_nil_for yield })
+        unmap_cached_nil_for(cache.fetch(key, cache_fetcher_options) do
+          map_cached_nil_for yield
+        end)
       else
         yield
       end
diff --git a/lib/identity_cache/cache_fetcher.rb b/lib/identity_cache/cache_fetcher.rb
index 2688bfc6..2a88a203 100644
--- a/lib/identity_cache/cache_fetcher.rb
+++ b/lib/identity_cache/cache_fetcher.rb
@@ -1,8 +1,52 @@
 # frozen_string_literal: true
+
+require 'securerandom'
+
 module IdentityCache
   class CacheFetcher
     attr_accessor :cache_backend
 
+    EMPTY_HASH = {}.freeze
+
+    class FillLock
+      FILL_LOCKED = :fill_locked
+      FAILED_CLIENT_ID = 'fill_failed'
+
+      class << self
+        def from_cache(marker, client_id, data_version)
+          raise ArgumentError unless marker == FILL_LOCKED
+          new(client_id: client_id, data_version: data_version)
+        end
+
+        def cache_value?(cache_value)
+          cache_value.is_a?(Array) && cache_value.length == 3 && cache_value.first == FILL_LOCKED
+        end
+      end
+
+      attr_reader :client_id, :data_version
+
+      def initialize(client_id:, data_version:)
+        @client_id = client_id
+        @data_version = data_version
+      end
+
+      def cache_value
+        [FILL_LOCKED, client_id, data_version]
+      end
+
+      def mark_failed
+        @client_id = FAILED_CLIENT_ID
+      end
+
+      def fill_failed?
+        @client_id == FAILED_CLIENT_ID
+      end
+
+      def ==(other)
+        self.class == other.class && client_id == other.client_id && data_version == other.data_version
+      end
+    end
+
     def initialize(cache_backend)
       @cache_backend = cache_backend
     end
@@ -25,27 +69,184 @@ def fetch_multi(keys, &block)
       results
     end
 
-    def fetch(key)
-      result = nil
-      yielded = false
-      @cache_backend.cas(key) do |value|
-        yielded = true
-        unless IdentityCache::DELETED == value
-          result = value
-          break
+    def fetch(key, fill_lock_duration: nil, lock_wait_limit: 2)
+      if fill_lock_duration && IdentityCache.should_fill_cache?
+        fetch_with_fill_lock(key, fill_lock_duration, lock_wait_limit) do
+          yield
+        end
+      else
+        fetch_without_fill_lock(key) { yield }
+      end
+    end
+
+    private
+
+    def fetch_without_fill_lock(key)
+      data = nil
+      upsert(key) do |value|
+        value = nil if value == IdentityCache::DELETED || FillLock.cache_value?(value)
+        unless value.nil?
+          return value
         end
-        result = yield
+        data = yield
         break unless IdentityCache.should_fill_cache?
-        result
+        data
+      end
+      data
+    end
+
+    def fetch_with_fill_lock(key, fill_lock_duration, lock_wait_limit)
+      raise ArgumentError, 'fill_lock_duration must be greater than 0.0' unless fill_lock_duration > 0.0
+      raise ArgumentError, 'lock_wait_limit must be greater than 0' unless lock_wait_limit > 0
+      lock = nil
+      using_fallback_key = false
+      expiration_options = EMPTY_HASH
+      (lock_wait_limit + 2).times do # +2 is for first attempt and retry with fallback key
+        result = fetch_or_take_lock(key, old_lock: lock, **expiration_options)
+        case result
+        when FillLock
+          lock = result
+          if lock.client_id == client_id # have lock
+            data = begin
+              yield
+            rescue
+              mark_fill_failure_on_lock(key, expiration_options)
+              raise
+            end
+
+            if !fill_with_lock(key, data, lock, expiration_options) && !using_fallback_key
+              # fallback to storing data in the fallback key so it is available to clients waiting on the lock
+              expiration_options = fallback_key_expiration_options(fill_lock_duration)
+              @cache_backend.write(lock_fill_fallback_key(key, lock), data, **expiration_options)
+            end
+            return data
+          else
+            raise LockWaitTimeout if lock_wait_limit <= 0
+            lock_wait_limit -= 1
+
+            # If fill failed in the other client, then it might be failing fast
+            # so avoid waiting the typical amount of time for a lock wait. The
+            # semian gem can be used to handle failing fast when the database is slow.
+            if lock.fill_failed?
+              return fetch_without_fill_lock(key) { yield }
+            end
+
+            # lock wait
+            sleep(fill_lock_duration)
+            # loop around to retry fetch_or_take_lock
+          end
+        when IdentityCache::DELETED # interrupted by cache invalidation
+          if lock && !using_fallback_key
+            # cache invalidated during lock wait, try fallback key
+            using_fallback_key = true
+            key = lock_fill_fallback_key(key, lock)
+            expiration_options = fallback_key_expiration_options(fill_lock_duration)
+            # loop around to retry with fallback key
+          else
+            # cache invalidation prevented lock from being taken
+            return yield
+          end
+        when nil # Errors talking to memcached
+          return yield
+        else # hit
+          return result
+        end
+      end
+      raise "unexpected number of loop iterations"
+    end
+
+    def mark_fill_failure_on_lock(key, expiration_options)
+      @cache_backend.cas(key, **expiration_options) do |value|
+        break unless FillLock.cache_value?(value)
+        lock = FillLock.from_cache(*value)
+        break if lock.client_id != client_id
+        lock.mark_failed
+        lock.cache_value
+      end
+    end
+
+    def upsert(key, expiration_options = EMPTY_HASH)
+      yielded = false
+      upserted = @cache_backend.cas(key, expiration_options) do |value|
+        yielded = true
+        yield value
       end
       unless yielded
-        result = yield
-        add(key, result)
+        data = yield nil
+        upserted = add(key, data, expiration_options)
       end
-      result
+      upserted
     end
 
-    private
+    def fetch_or_take_lock(key, old_lock:, **expiration_options)
+      new_lock = nil
+      upserted = upsert(key, expiration_options) do |value|
+        if value.nil? || value == IdentityCache::DELETED
+          if old_lock # cache invalidated
+            return value
+          else
+            new_lock = FillLock.new(client_id: client_id, data_version: SecureRandom.uuid)
+          end
+        elsif FillLock.cache_value?(value)
+          fetched_lock = FillLock.from_cache(*value)
+          if old_lock == fetched_lock
+            # preserve data version since there hasn't been any cache invalidations
+            new_lock = FillLock.new(client_id: client_id, data_version: old_lock.data_version)
+          else
+            return fetched_lock
+          end
+        else # hit
+          return value
+        end
+        new_lock.cache_value # take lock
+      end
+
+      return new_lock if upserted
+
+      value = @cache_backend.read(key)
+      if FillLock.cache_value?(value)
+        FillLock.from_cache(*value)
+      else
+        value
+      end
+    end
+
+    def fill_with_lock(key, data, my_lock, expiration_options)
+      upserted = upsert(key, expiration_options) do |value|
+        return false if value.nil? || value == IdentityCache::DELETED
+        return true unless FillLock.cache_value?(value) # already filled
+        current_lock = FillLock.from_cache(*value)
+        if current_lock.data_version != my_lock.data_version
+          return false # invalidated then relocked
+        end
+        data
+      end
+
+      upserted
+    end
+
+    def lock_fill_fallback_key(key, lock)
+      "lock_fill:#{lock.data_version}:#{key}"
+    end
+
+    def fallback_key_expiration_options(fill_lock_duration)
+      # Override the default TTL for the fallback key lock since it won't be used for very long.
+      expires_in = fill_lock_duration * 2
+
+      # memcached uses integer number of seconds for TTL so round up to avoid having
+      # the cache store round down with `to_i`
+      expires_in = expires_in.ceil
+
+      # memcached TTL only gets part of the first second (https://github.com/memcached/memcached/issues/307),
+      # so increase TTL by 1 to compensate
+      expires_in += 1
+
+      { expires_in: expires_in }
+    end
+
+    def client_id
+      @client_id ||= SecureRandom.uuid
+    end
 
     def cas_multi(keys)
       result = nil
@@ -81,8 +282,9 @@ def add_multi(keys)
       result.each { |k, v| add(k, v) }
     end
 
-    def add(key, value)
-      @cache_backend.write(key, value, unless_exist: true) if IdentityCache.should_fill_cache?
+    def add(key, value, **expiration_options)
+      return false unless IdentityCache.should_fill_cache?
+      @cache_backend.write(key, value, unless_exist: true, **expiration_options)
     end
   end
 end
diff --git a/lib/identity_cache/fallback_fetcher.rb b/lib/identity_cache/fallback_fetcher.rb
index 4813678c..e9de39d7 100644
--- a/lib/identity_cache/fallback_fetcher.rb
+++ b/lib/identity_cache/fallback_fetcher.rb
@@ -32,7 +32,10 @@ def fetch_multi(keys)
       results
     end
 
-    def fetch(key)
+    def fetch(key, unsupported_options = {})
+      unless unsupported_options.empty?
+        raise ArgumentError, "unsupported keywords: #{unsupported_options.keys.join(', ')}"
+      end
       result = @cache_backend.read(key)
       if result.nil?
         result = yield
diff --git a/lib/identity_cache/memoized_cache_proxy.rb b/lib/identity_cache/memoized_cache_proxy.rb
index 3e7de755..cf5be9ff 100644
--- a/lib/identity_cache/memoized_cache_proxy.rb
+++ b/lib/identity_cache/memoized_cache_proxy.rb
@@ -59,7 +59,7 @@ def delete(key)
       end
     end
 
-    def fetch(key)
+    def fetch(key, cache_fetcher_options = {})
       memo_misses = 0
       cache_misses = 0
 
@@ -68,7 +68,7 @@ def fetch(key)
 
         value = fetch_memoized(key) do
           memo_misses = 1
-          @cache_fetcher.fetch(key) do
+          @cache_fetcher.fetch(key, cache_fetcher_options) do
             cache_misses = 1
             instrument_duration(payload, :resolve_miss_time) do
               yield
diff --git a/lib/identity_cache/query_api.rb b/lib/identity_cache/query_api.rb
index de33f28a..07220615 100644
--- a/lib/identity_cache/query_api.rb
+++ b/lib/identity_cache/query_api.rb
@@ -17,9 +17,30 @@ def exists_with_identity_cache?(id)
         !!fetch_by_id(id)
       end
 
-      # Default fetcher added to the model on inclusion, it behaves like
-      # ActiveRecord::Base.where(id: id).first
-      def fetch_by_id(id, includes: nil)
+      # Fetch the record by its primary key from the cache or read from
+      # the database and fill the cache on a cache miss. This behaves like
+      # `where(id: id).readonly.first` being called on the model.
+      #
+      # @param id Primary key value for the record to fetch.
+      # @param includes [Hash|Array|Symbol] Cached associations to prefetch from
+      #   the cache on the returned record
+      # @param fill_lock_duration [Float] If provided, take a fill lock around cache fills
+      #   and wait for this duration for cache to be filled when reading a lock provided
+      #   by another client. Defaults to not setting the fill lock and trying to fill the
+      #   cache from the database regardless of the presence of another client's fill lock.
+      #   Set this to just above the typical amount of time it takes to do a cache fill.
+      # @param lock_wait_limit [Integer] Only applicable if fill_lock_duration is provided,
+      #   in which case it specifies the number of times to do a lock wait. After the first
+      #   lock wait it will try to take the lock, so will only do following lock waits due
+      #   to another client taking the lock first. If another lock wait would be needed after
+      #   reaching the limit, then a `LockWaitTimeout` exception is raised. Default is 2. Use
+      #   this to control the maximum total lock wait duration
+      #   (`lock_wait_limit * fill_lock_duration`).
+      # @raise [LockWaitTimeout] Timeout after waiting `lock_wait_limit * fill_lock_duration`
+      #   seconds for `lock_wait_limit` other clients to fill the cache.
+      # @return [self|nil] An instance of this model for the record with the specified id or
+      #   `nil` if no record with this `id` exists in the database
+      def fetch_by_id(id, includes: nil, **cache_fetcher_options)
         ensure_base_model
         raise_if_scoped
         raise NotImplementedError, "fetching needs the primary index enabled" unless primary_cache_index_enabled
@@ -27,7 +48,7 @@ def fetch_by_id(id, includes: nil)
         return unless id
         record = if should_use_cache?
           object = nil
-          coder  = IdentityCache.fetch(rails_cache_key(id)) do
+          coder  = IdentityCache.fetch(rails_cache_key(id), cache_fetcher_options) do
             Encoder.encode(object = resolve_cache_miss(id))
           end
           object ||= Encoder.decode(coder, self)
@@ -48,13 +69,17 @@ def fetch_by_id(id, includes: nil)
         record
       end
 
-      # Default fetcher added to the model on inclusion, it behaves like
-      # ActiveRecord::Base.find, will raise ActiveRecord::RecordNotFound exception
-      # if id is not in the cache or the db.
-      def fetch(id, includes: nil)
-        fetch_by_id(id, includes: includes) or raise(
-          ActiveRecord::RecordNotFound, "Couldn't find #{name} with ID=#{id}"
-        )
+      # Fetch the record by its primary key from the cache or read from
+      # the database and fill the cache on a cache miss. This behaves like
+      # `readonly.find(id)` being called on the model.
+      #
+      # @param (see #fetch_by_id)
+      # @raise (see #fetch_by_id)
+      # @raise [ActiveRecord::RecordNotFound] if the record isn't found
+      # @return [self] An instance of this model for the record with the specified id
+      def fetch(id, options = {})
+        fetch_by_id(id, options) or
+          raise(ActiveRecord::RecordNotFound, "Couldn't find #{name} with ID=#{id}")
       end
 
       # Default fetcher added to the model on inclusion, if behaves like
diff --git a/test/attribute_cache_test.rb b/test/attribute_cache_test.rb
index e4990b7b..a1c616c3 100644
--- a/test/attribute_cache_test.rb
+++ b/test/attribute_cache_test.rb
@@ -20,7 +20,7 @@ def test_attribute_values_are_fetched_and_returned_on_cache_misses
     assert_queries(1) do
       assert_equal 'foo', AssociatedRecord.fetch_name_by_id(1)
     end
-    assert(fetch.has_been_called_with?(@name_attribute_key))
+    assert(fetch.has_been_called_with?(@name_attribute_key, {}))
   end
 
   def test_attribute_values_are_returned_on_cache_hits
diff --git a/test/cache_fetcher_test.rb b/test/cache_fetcher_test.rb
new file mode 100644
index 00000000..b51bc0a1
--- /dev/null
+++ b/test/cache_fetcher_test.rb
@@ -0,0 +1,161 @@
+# frozen_string_literal: true
+
+require "test_helper"
+require "socket"
+
+class CacheFetcherTest < IdentityCache::TestCase
+  attr_reader :key, :cache_fetcher
+
+  def setup
+    super
+    @cache_fetcher = IdentityCache::CacheFetcher.new(backend)
+    @key = "key"
+  end
+
+  def test_fetch_without_lock_miss
+    assert_memcache_operations(2) do # get, add
+      assert_equal(:fill_data, cache_fetcher.fetch(key) { :fill_data })
+    end
+    assert_equal(:fill_data, backend.read(key))
+  end
+
+  def test_fetch_miss
+    assert_memcache_operations(3) do # get (miss), add (lock), get+cas (fill)
+      assert_equal(:fill_data, cache_fetcher.fetch(key, fill_lock_duration: 0.9) { :fill_data })
+    end
+    assert_equal(:fill_data, backend.read(key))
+  end
+
+  def test_fetch_hit
+    cache_fetcher.fetch(key) { :hit_data }
+    assert_memcache_operations(1) do # get
+      assert_equal :hit_data, cache_fetcher.fetch(key, fill_lock_duration: 0.9) { flunk("unexpected yield") }
+    end
+  end
+
+  def test_fetch_lock_wait
+    other_client_takes_lock
+
+    # fill during lock wait
+    other_client_operations = 1
+    cache_fetcher.expects(:sleep).with do |duration|
+      assert_memcache_operations(other_client_operations) do # get+cas
+        other_cache_fetcher.fetch(key) { :fill_data }
+      end
+      duration == 0.9
+    end
+
+    assert_memcache_operations(2 + other_client_operations) do # get (miss), get (hit)
+      assert_equal :fill_data, cache_fetcher.fetch(key, fill_lock_duration: 0.9) { flunk "unexpected yield" }
+    end
+  end
+
+  def test_fetch_lock_wait_timeout
+    other_client_takes_lock
+
+    cache_fetcher.expects(:sleep).with(0.9)
+    assert_memcache_operations(3) do # get (miss), get+cas (miss, take lock), get+cas (fill)
+      assert_equal(:fill_data, cache_fetcher.fetch(key, fill_lock_duration: 0.9) { :fill_data })
+    end
+    assert_equal(:fill_data, backend.read(key))
+  end
+
+  def test_fetch_lock_wait_with_cache_invalidation
+    other_client_takes_lock
+
+    # invalidate during lock wait
+    other_client_operations = 1
+    cache_fetcher.expects(:sleep).with do |duration|
+      assert_memcache_operations(other_client_operations) do # get+cas
+        other_cache_fetcher.delete(key)
+      end
+      duration == 0.9
+    end
+
+    assert_memcache_operations(3 + other_client_operations) do # get (miss), get (invalidated), get (fallback key)
+      assert_equal(:fill_data, cache_fetcher.fetch(key, fill_lock_duration: 0.9) { :fill_data })
+    end
+    assert_equal(IdentityCache::DELETED, backend.read(key))
+  end
+
+  def test_fetch_lock_wait_limit_reached
+    data_version = SecureRandom.uuid
+    lock = write_lock(data_version: data_version)
+    other_client_operations = 3
+    cache_fetcher.expects(:sleep).times(3).with do |duration|
+      lock = write_lock(data_version: data_version)
+      duration == 0.9
+    end
+    assert_memcache_operations(4 + other_client_operations) do # get (miss) * 4
+      assert_raises(IdentityCache::LockWaitTimeout) do
+        cache_fetcher.fetch(key, fill_lock_duration: 0.9, lock_wait_limit: 3)
+      end
+    end
+    assert_equal(lock, backend.read(key))
+  end
+
+  def test_fetch_lock_attempt_interrupted_with_cache_invalidation
+    cache_fetcher.expects(:sleep).never
+    backend.expects(:cas).returns(false).with do |got_key|
+      other_cache_fetcher.delete(key)
+      key == got_key
+    end
+    other_client_operations = 1
+    assert_memcache_operations(2 + other_client_operations) do # add (lock), get (lock), excludes mocked cas
+      assert_equal(:fill_data, cache_fetcher.fetch(key, fill_lock_duration: 0.9) { :fill_data })
+    end
+    assert_equal(IdentityCache::DELETED, backend.read(key))
+  end
+
+  def test_fetch_with_memcached_down
+    cache_fetcher = IdentityCache::CacheFetcher.new(unconnected_cache_backend)
+    cache_fetcher.expects(:sleep).never
+    # 3 operations because the underlying cache store doesn't distinguish between
+    # request failures and error responses (e.g. NOT_FOUND or NOT_STORED)
+    assert_memcache_operations(3) do # get (miss), add (lock), get (read lock)
+      assert_equal(:miss_data, cache_fetcher.fetch(key, fill_lock_duration: 0.9) { :miss_data })
+    end
+  end
+
+  def test_fetch_with_database_down
+    IdentityCache::CacheFetcher.any_instance.expects(:sleep).never
+    exc = assert_raises(RuntimeError) do
+      other_cache_fetcher.fetch(key, fill_lock_duration: 0.9) { raise 'database down' }
+    end
+    assert_equal('database down', exc.message)
+    exc = assert_raises(RuntimeError) do
+      cache_fetcher.fetch(key, fill_lock_duration: 0.9) { raise 'database still down' }
+    end
+    assert_equal('database still down', exc.message)
+  end
+
+  private
+
+  def write_lock(client_id: SecureRandom.uuid, data_version:)
+    lock = IdentityCache::CacheFetcher::FillLock.new(client_id: client_id, data_version: data_version)
+    other_cache_fetcher.write(key, lock)
+    lock
+  end
+
+  def other_client_takes_lock
+    other_cache_fetcher.fetch(key, fill_lock_duration: 0.9) do
+      break # skip filling
+    end
+  end
+
+  def other_cache_fetcher
+    @other_cache_fetcher ||= IdentityCache::CacheFetcher.new(backend)
+  end
+
+  def unconnected_cache_backend
+    ActiveSupport::Cache::MemcachedStore.new("127.0.0.1:#{open_port}", support_cas: true)
+  end
+
+  def open_port
+    socket = Socket.new(:INET, :STREAM)
+    socket.bind(Addrinfo.tcp('127.0.0.1', 0))
+    socket.local_address.ip_port
+  ensure
+    socket&.close
+  end
+end
diff --git a/test/denormalized_has_one_test.rb b/test/denormalized_has_one_test.rb
index e93b1506..8aea96db 100644
--- a/test/denormalized_has_one_test.rb
+++ b/test/denormalized_has_one_test.rb
@@ -24,12 +24,12 @@ def test_on_cache_miss_record_should_embed_associated_object
     assert_equal(@record.associated, record_from_cache_miss.fetch_associated)
     assert(
       fetch.has_been_called_with?(
-        @record.attribute_cache_key_for_attribute_and_current_values(:id, [:title], true)
+        @record.attribute_cache_key_for_attribute_and_current_values(:id, [:title], true), {}
       )
     )
     assert(
       fetch.has_been_called_with?(
-        @record.primary_cache_index_key
+        @record.primary_cache_index_key, {}
       )
     )
   end
@@ -52,12 +52,12 @@ def test_on_cache_miss_record_should_embed_nil_object
     end
     assert(
       fetch.has_been_called_with?(
-        @record.attribute_cache_key_for_attribute_and_current_values(:id, [:title], true)
+        @record.attribute_cache_key_for_attribute_and_current_values(:id, [:title], true), {}
       )
     )
     assert(
       fetch.has_been_called_with?(
-        @record.primary_cache_index_key
+        @record.primary_cache_index_key, {}
       )
     )
   end
diff --git a/test/fetch_test.rb b/test/fetch_test.rb
index 84c9a0c7..1b35a207 100644
--- a/test/fetch_test.rb
+++ b/test/fetch_test.rb
@@ -23,13 +23,13 @@ def test_fetch_with_garbage_input
   end
 
   def test_fetch_cache_hit
-    IdentityCache.cache.expects(:fetch).with(@blob_key).returns(@cached_value)
+    IdentityCache.cache.expects(:fetch).with(@blob_key, {}).returns(@cached_value)
 
     assert_equal(@record, Item.fetch(1))
   end
 
   def test_fetch_cache_hit_publishes_hydration_notification
-    IdentityCache.cache.expects(:fetch).with(@blob_key).returns(@cached_value)
+    IdentityCache.cache.expects(:fetch).with(@blob_key, {}).returns(@cached_value)
 
     events = 0
     subscriber = ActiveSupport::Notifications.subscribe('hydration.identity_cache') do |_, _, _, _, payload|
@@ -43,7 +43,7 @@ def test_fetch_cache_hit_publishes_hydration_notification
   end
 
   def test_fetch_cache_hit_publishes_cache_notification
-    IdentityCache.cache.cache_fetcher.expects(:fetch).with(@blob_key).returns(@cached_value)
+    IdentityCache.cache.cache_fetcher.expects(:fetch).with(@blob_key, {}).returns(@cached_value)
     expected = { memoizing: false, resolve_miss_time: 0, memo_hits: 0, cache_hits: 1, cache_misses: 0 }
 
     events = 0
@@ -59,7 +59,7 @@ def test_fetch_cache_hit_publishes_cache_notification
 
   def test_fetch_memoized_hit_publishes_cache_notification
     subscriber = nil
-    IdentityCache.cache.cache_fetcher.expects(:fetch).with(@blob_key).returns(@cached_value)
+    IdentityCache.cache.cache_fetcher.expects(:fetch).with(@blob_key, {}).returns(@cached_value)
     expected = { memoizing: true, resolve_miss_time: 0, memo_hits: 1, cache_hits: 0, cache_misses: 0 }
 
     IdentityCache.cache.with_memoization do
@@ -81,7 +81,7 @@ def test_fetch_hit_cache_namespace
     IdentityCache.cache_namespace = proc { |model| "#{model.table_name}:#{old_ns}" }
 
     new_blob_key = "items:#{@blob_key}"
-    IdentityCache.cache.expects(:fetch).with(new_blob_key).returns(@cached_value)
+    IdentityCache.cache.expects(:fetch).with(new_blob_key, {}).returns(@cached_value)
 
     assert_equal(@record, Item.fetch(1))
   ensure
@@ -89,7 +89,7 @@ def test_fetch_hit_cache_namespace
   end
 
   def test_exists_with_identity_cache_when_cache_hit
-    IdentityCache.cache.expects(:fetch).with(@blob_key).returns(@cached_value)
+    IdentityCache.cache.expects(:fetch).with(@blob_key, {}).returns(@cached_value)
 
     assert(Item.exists_with_identity_cache?(1))
   end
@@ -99,7 +99,7 @@ def test_exists_with_identity_cache_when_cache_miss_and_in_db
     Item.expects(:resolve_cache_miss).with(1).once.returns(@record)
 
     assert(Item.exists_with_identity_cache?(1))
-    assert(fetch.has_been_called_with?(@blob_key))
+    assert(fetch.has_been_called_with?(@blob_key, {}))
   end
 
   def test_exists_with_identity_cache_when_cache_miss_and_not_in_db
@@ -107,7 +107,7 @@ def test_exists_with_identity_cache_when_cache_miss_and_not_in_db
     Item.expects(:resolve_cache_miss).with(1).once.returns(nil)
 
     assert(!Item.exists_with_identity_cache?(1))
-    assert(fetch.has_been_called_with?(@blob_key))
+    assert(fetch.has_been_called_with?(@blob_key, {}))
   end
 
   def test_fetch_miss_published_dehydration_notification
@@ -147,7 +147,7 @@ def test_fetch_miss
     fetch = Spy.on(IdentityCache.cache, :fetch).and_return { |_, &block| block.call.tap { |result| results << result } }
 
     assert_equal(@record, Item.fetch(1))
-    assert(fetch.has_been_called_with?(@blob_key))
+    assert(fetch.has_been_called_with?(@blob_key, {}))
     assert_equal([@cached_value], results)
   end
 
@@ -162,11 +162,11 @@ def test_fetch_conflict
       @record.expire_cache
       @record
     end
-    add = Spy.on(fetcher, :add).and_call_through
+    write = Spy.on(backend, :write).and_call_through
 
     assert_equal(@record, Item.fetch(1))
     assert(resolve_cache_miss.has_been_called_with?(1))
-    assert(add.has_been_called_with?(@blob_key, @cached_value))
+    assert(write.has_been_called_with?(@blob_key, @cached_value, unless_exist: true))
     assert_equal(IdentityCache::DELETED, backend.read(@record.primary_cache_index_key))
   end
 
@@ -178,24 +178,24 @@ def test_fetch_conflict_after_delete
       @record.expire_cache
       @record
     end
-    add = Spy.on(IdentityCache.cache.cache_fetcher, :add).and_call_through
+    write = Spy.on(backend, :write).and_call_through
 
     assert_equal(@record, Item.fetch(1))
     assert(resolve_cache_miss.has_been_called_with?(1))
-    refute(add.has_been_called?)
+    refute(write.calls.any? { |call| call.args.last.key?(unless_exist: true) })
     assert_equal(IdentityCache::DELETED, backend.read(@record.primary_cache_index_key))
   end
 
   def test_fetch_by_id_not_found_should_return_nil
     nonexistent_record_id = 10
-    fetcher.expects(:add).with(@blob_key + '0', IdentityCache::CACHED_NIL)
+    fetcher.expects(:add).with(@blob_key + '0', IdentityCache::CACHED_NIL, {})
 
     assert_nil(Item.fetch_by_id(nonexistent_record_id))
   end
 
   def test_fetch_not_found_should_raise
     nonexistent_record_id = 10
-    fetcher.expects(:add).with(@blob_key + '0', IdentityCache::CACHED_NIL)
+    fetcher.expects(:add).with(@blob_key + '0', IdentityCache::CACHED_NIL, {})
 
     assert_raises(ActiveRecord::RecordNotFound) { Item.fetch(nonexistent_record_id) }
   end
@@ -219,7 +219,7 @@ def test_fetch_id_coercion
 
   def test_fetch_by_title_hit
     values = []
-    fetch = Spy.on(IdentityCache.cache, :fetch).and_return do |key, &block|
+    fetch = Spy.on(IdentityCache.cache, :fetch, {}).and_return do |key, &block|
       case key
       # Read record with title bob
       when @index_key then block.call.tap { |val| values << val }
@@ -233,35 +233,28 @@ def test_fetch_by_title_hit
 
     assert_equal(@record, Item.fetch_by_title('bob'))
     assert_equal([1], values)
-    assert(fetch.has_been_called_with?(@index_key))
-    assert(fetch.has_been_called_with?(@blob_key))
+    assert(fetch.has_been_called_with?(@index_key, {}))
+    assert(fetch.has_been_called_with?(@blob_key, {}))
   end
 
   def test_fetch_by_title_cache_namespace
     Item.send(:include, SwitchNamespace)
-    IdentityCache.cache.expects(:fetch).with("ns:#{@index_key}").returns(1)
-    IdentityCache.cache.expects(:fetch).with("ns:#{@blob_key}").returns(@cached_value)
+    IdentityCache.cache.expects(:fetch).with("ns:#{@index_key}", {}).returns(1)
+    IdentityCache.cache.expects(:fetch).with("ns:#{@blob_key}", {}).returns(@cached_value)
 
     assert_equal(@record, Item.fetch_by_title('bob'))
   end
 
-  def test_fetch_by_title_stores_idcnil
-    Item.connection.expects(:exec_query).once.returns(ActiveRecord::Result.new([], []))
-    add = Spy.on(fetcher, :add).and_call_through
-    fetch = Spy.on(fetcher, :fetch).and_call_through
-    assert_nil(Item.fetch_by_title('bob')) # exec_query => nil
-
-    assert_nil(Item.fetch_by_title('bob')) # returns cached nil
-    assert_nil(Item.fetch_by_title('bob')) # returns cached nil
-
-    assert(add.has_been_called_with?(@index_key, IdentityCache::CACHED_NIL))
-    assert_equal(3, fetch.calls.length)
+  def test_fetch_by_title_caches_nil
+    assert_nil(Item.fetch_by_title('missing'))
+    assert_no_queries do
+      assert_nil(Item.fetch_by_title('missing'))
+    end
   end
 
   def test_fetch_by_bang_method
-    Item.connection.expects(:exec_query).returns(ActiveRecord::Result.new([], []))
     assert_raises ActiveRecord::RecordNotFound do
-      Item.fetch_by_title!('bob')
+      Item.fetch_by_title!('missing')
     end
   end
 
@@ -306,7 +299,7 @@ def test_fetch_on_derived_model_raises
 
   def test_returned_records_are_readonly_on_cache_hit
     IdentityCache.with_fetch_read_only_records do
-      IdentityCache.cache.expects(:fetch).with(@blob_key).returns(@cached_value)
+      IdentityCache.cache.expects(:fetch).with(@blob_key, {}).returns(@cached_value)
       assert Item.fetch(1).readonly?
     end
   end
@@ -317,7 +310,7 @@ def test_returned_records_are_readonly_on_cache_miss
       Item.expects(:resolve_cache_miss).with(1).once.returns(@record)
 
       assert Item.exists_with_identity_cache?(1)
-      assert fetch.has_been_called_with?(@blob_key)
+      assert fetch.has_been_called_with?(@blob_key, {})
       assert Item.fetch(1).readonly?
     end
   end
@@ -330,7 +323,7 @@ def test_returned_records_are_not_readonly_with_open_transactions
         Item.expects(:resolve_cache_miss).with(1).once.returns(@record)
 
         refute IdentityCache.should_use_cache?
-        refute fetch.has_been_called_with?(@blob_key)
+        refute fetch.has_been_called_with?(@blob_key, {})
         refute Item.fetch(1).readonly?, "Fetched item was read-only"
       end
     end
@@ -346,4 +339,26 @@ def test_respects_should_use_cache_on_record
       end
     end
   end
+
+  def test_fetch_supports_lock_wait_options
+    @record.save
+
+    # only one client reads from the database on concurrent fetch with lock wait
+    assert_queries(1) do
+      # other client takes fill lock
+      cache_key = Item.rails_cache_key(@record.id)
+      lock = IdentityCache::CacheFetcher::FillLock.new(client_id: SecureRandom.uuid, data_version: SecureRandom.uuid)
+      IdentityCache.cache.cache_fetcher.write(cache_key, lock.cache_value)
+
+      # fetch waits on lock
+      IdentityCache.cache.cache_fetcher.expects(:sleep).with do |duration|
+        # other client fills cache
+        assert_queries(1) { Item.fetch(@record.id) }
+        duration == 0.1
+      end
+      Item.fetch(@record.id, fill_lock_duration: 0.1, lock_wait_limit: 1)
+
+      assert_equal @record, Item.fetch(@record.id)
+    end
+  end
 end
diff --git a/test/memoized_cache_proxy_test.rb b/test/memoized_cache_proxy_test.rb
index 7487a199..ff1b4c46 100644
--- a/test/memoized_cache_proxy_test.rb
+++ b/test/memoized_cache_proxy_test.rb
@@ -41,7 +41,7 @@ def test_fetch_should_short_circuit_on_falsy_memoized_values
   end
 
   def test_fetch_should_try_memcached_on_not_memoized_values
-    fetcher.expects(:fetch).with('foo').returns('bar')
+    fetcher.expects(:fetch).with('foo', {}).returns('bar')
 
     IdentityCache.cache.with_memoization do
       assert_equal 'bar', IdentityCache.cache.fetch('foo')
diff --git a/test/readonly_test.rb b/test/readonly_test.rb
index 67e59a8f..ddc10b3e 100644
--- a/test/readonly_test.rb
+++ b/test/readonly_test.rb
@@ -47,7 +47,7 @@ def test_fetch_should_not_update_cache
       assert_equal @record, Item.fetch(1)
     end
     assert_nil(backend.read(@record.primary_cache_index_key))
-    assert(fetch.has_been_called_with?(@record.primary_cache_index_key))
+    assert(fetch.has_been_called_with?(@record.primary_cache_index_key, {}))
   end
 
   def test_fetch_multi_should_not_update_cache