fix: `nil` in `OrderedCache` (#10647)

* fix: `nil` in `OrderedCache`

* Update CHANGELOG

---------

Co-authored-by: Viktor Baranov <baranov.viktor.27@gmail.com>

CHANGELOG.md

@@ -31,6 +31,7 @@
 
 ### 🐛 Bug Fixes
 
+- nil in OrderedCache ([#10647](https://github.com/blockscout/blockscout/pull/10647))
 - Fix for metadata detection at ipfs protocol([#10646](https://github.com/blockscout/blockscout/pull/10646))
 - Change default shrink internal_transactions table migration params ([#10644](https://github.com/blockscout/blockscout/pull/10644))
 - Fix bug in update_replaced_transactions query ([#10634](https://github.com/blockscout/blockscout/issues/10634))

apps/explorer/lib/explorer/chain.ex

@@ -1638,7 +1638,7 @@ defmodule Explorer.Chain do
   end
 
   defp block_from_cache(block_type, paging_options, necessity_by_association, options) do
-    case Blocks.take_enough(paging_options.page_size) do
+    case Blocks.atomic_take_enough(paging_options.page_size) do
       nil ->
         elements = fetch_blocks(block_type, paging_options, necessity_by_association, options)
 
@@ -1652,7 +1652,7 @@ defmodule Explorer.Chain do
   end
 
   def uncles_from_cache(block_type, paging_options, necessity_by_association, options) do
-    case Uncles.take_enough(paging_options.page_size) do
+    case Uncles.atomic_take_enough(paging_options.page_size) do
       nil ->
         elements = fetch_blocks(block_type, paging_options, necessity_by_association, options)
 
@@ -2620,7 +2620,7 @@ defmodule Explorer.Chain do
       if is_nil(paging_options.key) or paging_options.page_number == 1 do
         paging_options.page_size
         |> Kernel.+(1)
-        |> Transactions.take_enough()
+        |> Transactions.atomic_take_enough()
         |> case do
           nil ->
             transactions = fetch_recent_collated_transactions_for_rap(paging_options, necessity_by_association)

apps/explorer/lib/explorer/chain/address.ex

@@ -328,7 +328,7 @@ defmodule Explorer.Chain.Address do
 
     if is_nil(paging_options.key) do
       paging_options.page_size
-      |> Accounts.take_enough()
+      |> Accounts.atomic_take_enough()
       |> case do
         nil ->
           get_addresses(options)

apps/explorer/lib/explorer/chain/ordered_cache.ex

@@ -112,6 +112,11 @@ defmodule Explorer.Chain.OrderedCache do
   """
   @callback take_enough(integer()) :: [element] | nil
 
+  @doc """
+  Behaves like `take_enough/1`, but addresses [#10445](https://github.com/blockscout/blockscout/issues/10445).
+  """
+  @callback atomic_take_enough(integer()) :: [element] | nil
+
   @doc """
   Adds an element, or a list of elements, to the cache.
   When the cache is full, only the most prevailing elements will be stored, based
@@ -204,6 +209,22 @@ defmodule Explorer.Chain.OrderedCache do
         end
       end
 
+      @impl OrderedCache
+      def atomic_take_enough(amount) do
+        items =
+          cache_name()
+          |> ConCache.ets()
+          |> :ets.tab2list()
+
+        if amount <= Enum.count(items) - 1 do
+          items
+          |> Enum.reject(fn {key, _value} -> key == ids_list_key() end)
+          |> Enum.sort(&prevails?/2)
+          |> Enum.take(amount)
+          |> Enum.map(fn {_key, value} -> value end)
+        end
+      end
+
       ### Updating function
 
       def remove_deleted_from_index({:delete, _cache_pid, id}) do