Deduplicate various Active Record schema cache structures

Real world database schemas contain a lot of duplicated data.
Some column names like `id`, `created_at` etc can easily be repeated
hundreds of times. Same for SqlTypeMetada, most database will contain
only a limited number of possible combinations.

This result in a lot of wasted memory.

The idea here is to make these data sctructures immutable, use a registry
to substitute similar instances with pre-existing ones.

1 files changed, 10 insertions, 0 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/sql_type_metadata.rb b/activerecord/lib/active_record/connection_adapters/sql_type_metadata.rb
index df28df7a7c..969867e70f 100644
--- a/activerecord/lib/active_record/connection_adapters/sql_type_metadata.rb
+++ b/activerecord/lib/active_record/connection_adapters/sql_type_metadata.rb
@@ -1,9 +1,13 @@
 # frozen_string_literal: true
 
+require "active_record/connection_adapters/deduplicable"
+
 module ActiveRecord
   # :stopdoc:
   module ConnectionAdapters
     class SqlTypeMetadata
+      include Deduplicable
+
       attr_reader :sql_type, :type, :limit, :precision, :scale
 
       def initialize(sql_type: nil, type: nil, limit: nil, precision: nil, scale: nil)
@@ -32,6 +36,12 @@ module ActiveRecord
           precision.hash >> 1 ^
           scale.hash >> 2
       end
+
+      private
+        def deduplicated
+          @sql_type = -sql_type
+          super
+        end
     end
   end
 end