Rails cache broken with Redis::Distributed in 7.0.7

[jdelStrother]

#48645 adds support for write_multi in collection caches, but this now breaks when using Redis::Distributed as a backend. eg:

      config.cache_store = :redis_cache_store, {
        url: [url1, url2],
        ...
      }
}

I'm seeing MAPPED_MSET cannot be used in Redis::Distributed because the keys involved need to be on the same server or because we cannot guarantee that the operation will be atomic.

redis (5.0.7) lib/redis/distributed.rb in mapped_mset at line 306
activesupport (7.0.7) lib/active_support/cache/redis_cache_store.rb in block (2 levels) in write_multi_entries at line 419
connection_pool (2.4.1) lib/connection_pool.rb in block (2 levels) in with at line 110
connection_pool (2.4.1) lib/connection_pool.rb in handle_interrupt at line 109
connection_pool (2.4.1) lib/connection_pool.rb in block in with at line 109
connection_pool (2.4.1) lib/connection_pool.rb in handle_interrupt at line 106
connection_pool (2.4.1) lib/connection_pool.rb in with at line 106
activesupport (7.0.7) lib/active_support/cache/redis_cache_store.rb in block in write_multi_entries at line 418
activesupport (7.0.7) lib/active_support/cache/redis_cache_store.rb in failsafe at line 466
activesupport (7.0.7) lib/active_support/cache/redis_cache_store.rb in write_multi_entries at line 416
activesupport (7.0.7) lib/active_support/cache.rb in block in write_multi at line 415
activesupport (7.0.7) lib/active_support/cache.rb in block in instrument at line 783
activesupport (7.0.7) lib/active_support/notifications.rb in block in instrument at line 206
activesupport (7.0.7) lib/active_support/notifications/instrumenter.rb in instrument at line 24
activesupport (7.0.7) lib/active_support/notifications.rb in instrument at line 206
activesupport (7.0.7) lib/active_support/cache.rb in instrument at line 783
activesupport (7.0.7) lib/active_support/cache.rb in write_multi at line 410
actionview (7.0.7) lib/action_view/renderer/partial_renderer/collection_caching.rb in fetch_or_cache_partial at line 106
actionview (7.0.7) lib/action_view/renderer/partial_renderer/collection_caching.rb in cache_collection_render at line 43
actionview (7.0.7) lib/action_view/renderer/collection_renderer.rb in block in render_collection at line 161
activesupport (7.0.7) lib/active_support/notifications.rb in block in instrument at line 206
activesupport (7.0.7) lib/active_support/notifications/instrumenter.rb in instrument at line 24
activesupport (7.0.7) lib/active_support/notifications.rb in instrument at line 206
actionview (7.0.7) lib/action_view/renderer/collection_renderer.rb in render_collection at line 147
actionview (7.0.7) lib/action_view/renderer/collection_renderer.rb in render_collection_with_partial at line 119
actionview (7.0.7) lib/action_view/renderer/renderer.rb in render_partial_to_object at line 72
actionview (7.0.7) lib/action_view/renderer/renderer.rb in render_to_object at line 27
actionview (7.0.7) lib/action_view/renderer/renderer.rb in render at line 22
actionview (7.0.7) lib/action_view/helpers/rendering_helper.rb in block in render at line 37
actionview (7.0.7) lib/action_view/base.rb in in_rendering_context at line 270
actionview (7.0.7) lib/action_view/helpers/rendering_helper.rb in render at line 33

@byroot perhaps this could be fixed in Redis::Distributed with something like this (pseudocode) ?

    def mapped_mset(hash, atomic: true)
      raise CannotDistribute, :mapped_mset if atomic
      
       hash.group_by { node_for(_1) }.each { |node, keyvalues|
            node.mapped_mset(keyvalues)
       }
    end

want me to take a stab at fixing it?

[byroot]

want me to take a stab at fixing it?

Sure, go ahead.

[skipkayhil]

Fixed in #48952