https://github.com/rails/rails/pull/13128

benchmark.rb

require 'benchmark'

def extract_schema_and_table(name)
  table, schema = name.scan(/[^".\s]+|"[^"]*"/)[0..1].collect{|m| m.gsub(/(^"|"$)/,'') }.reverse
  [schema, table]
end

def extract_pg_identifier_from_name(name)
  match_data = name.start_with?('"') ? name.match(/\"([^\"]+)\"/) : name.match(/([^\.]+)/)

  if match_data
    rest = name[match_data[0].length, name.length]
    rest = rest[1, rest.length] if rest.start_with? "."
    [match_data[1], (rest.length > 0 ? rest : nil)]
  end
end

n = 50_000
Benchmark.bm(7) do |x|
  x.report("connection.extract_pg_identifier_from_name:")   {
    n.times do
      extract_pg_identifier_from_name(%(my_schema.my_table))
      extract_pg_identifier_from_name(%(my_schema."my_table"))
      extract_pg_identifier_from_name(%("my_schema".my_table))
      extract_pg_identifier_from_name(%("my_schema"."my_table"))
      extract_pg_identifier_from_name(%(my_table))
      extract_pg_identifier_from_name(%("my_table"))
    end
  }
  x.report("Utils.extract_schema_and_table:") {
    n.times do
      extract_schema_and_table(%(my_schema.my_table))
      extract_schema_and_table(%(my_schema."my_table"))
      extract_schema_and_table(%("my_schema".my_table))
      extract_schema_and_table(%("my_schema"."my_table"))
      extract_schema_and_table(%(my_table))
      extract_schema_and_table(%("my_table"))
    end
  }
end

result.txt

activerecord :: (master*) » ruby benchmark.rb                                                                   ~/Projects/rails/activerecord
              user     system      total        real
connection.extract_pg_identifier_from_name:  1.080000   0.010000   1.090000 (  1.077225)
Utils.extract_schema_and_table:  2.470000   0.000000   2.470000 (  2.483858)