Active Record Cache

Active Record --- Connection Pool --- Database
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                    SchemaCache

Active Record caches:

• SchemaCache is a YAML file to prevent hit the database
• Columns ActiveRecord::ConnectionAdapters::SchemaCache — Model.columns_hash
• Query (ActiveRecord::ConnectionAdapters::QueryCache)
• AssociationCache ActiveRecord::Associations
• ActiveRecord::StatementCache

QueryCache, AssociationCache is simply a Hash.

clear_query_cache can clear query cache.

Calling reload will bust these caches.