Merge remote-tracking branch 'origin/master' into actioncable_logging

18 files changed, 212 insertions, 194 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb b/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb
index 7a2a1a0e33..7e0c9f7837 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb
@@ -69,7 +69,11 @@ module ActiveRecord
       end
       undef_method :select_rows
 
-      # Executes the SQL statement in the context of this connection.
+      # Executes the SQL statement in the context of this connection and returns
+      # the raw result from the connection adapter.
+      # Note: depending on your database connector, the result returned by this
+      # method may be manually memory managed. Consider using the exec_query
+      # wrapper instead.
       def execute(sql, name = nil)
       end
       undef_method :execute
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
index 690e0ba957..cb10ca9929 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
@@ -182,6 +182,7 @@ module ActiveRecord
           end
         CODE
       end
+      alias_method :numeric, :decimal
     end
 
     # Represents the schema of an SQL table in an abstract way. This class
@@ -436,6 +437,7 @@ module ActiveRecord
     #     t.bigint
     #     t.float
     #     t.decimal
+    #     t.numeric
     #     t.datetime
     #     t.timestamp
     #     t.time
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_dumper.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_dumper.rb
index a95109fdae..b1b6044e72 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_dumper.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_dumper.rb
@@ -14,7 +14,7 @@ module ActiveRecord
 
       def column_spec_for_primary_key(column)
         return if column.type == :integer
-        spec = { id: column.type.inspect }
+        spec = { id: schema_type(column).inspect }
         spec.merge!(prepare_column_options(column).delete_if { |key, _| [:name, :type].include?(key) })
       end
 
@@ -24,7 +24,7 @@ module ActiveRecord
       def prepare_column_options(column)
         spec = {}
         spec[:name]      = column.name.inspect
-        spec[:type]      = schema_type(column)
+        spec[:type]      = schema_type(column).to_s
         spec[:null]      = 'false' unless column.null
 
         if limit = schema_limit(column)
@@ -57,7 +57,7 @@ module ActiveRecord
       private
 
       def schema_type(column)
-        column.type.to_s
+        column.type
       end
 
       def schema_limit(column)
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
index 70868ebd03..f0f855963a 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
@@ -92,7 +92,9 @@ module ActiveRecord
 
       # Returns an array of Column objects for the table specified by +table_name+.
       # See the concrete implementation for details on the expected parameter values.
-      def columns(table_name) end
+      def columns(table_name)
+        raise NotImplementedError, "#columns is not implemented"
+      end
 
       # Checks to see if a column exists in a given table.
       #
@@ -110,18 +112,25 @@ module ActiveRecord
       #
       def column_exists?(table_name, column_name, type = nil, options = {})
         column_name = column_name.to_s
-        columns(table_name).any?{ |c| c.name == column_name &&
-                                      (!type                     || c.type == type) &&
-                                      (!options.key?(:limit)     || c.limit == options[:limit]) &&
-                                      (!options.key?(:precision) || c.precision == options[:precision]) &&
-                                      (!options.key?(:scale)     || c.scale == options[:scale]) &&
-                                      (!options.key?(:default)   || c.default == options[:default]) &&
-                                      (!options.key?(:null)      || c.null == options[:null]) }
+        checks = []
+        checks << lambda { |c| c.name == column_name }
+        checks << lambda { |c| c.type == type } if type
+        (migration_keys - [:name]).each do |attr|
+          checks << lambda { |c| c.send(attr) == options[attr] } if options.key?(attr)
+        end
+
+        columns(table_name).any? { |c| checks.all? { |check| check[c] } }
       end
 
       # Returns just a table's primary key
       def primary_key(table_name)
         pks = primary_keys(table_name)
+        warn <<-WARNING.strip_heredoc if pks.count > 1
+          WARNING: Rails does not support composite primary key.
+
+          #{table_name} has composite primary key. Composite primary key is ignored.
+        WARNING
+
         pks.first if pks.one?
       end
 
@@ -450,7 +459,7 @@ module ActiveRecord
       # The +type+ parameter is normally one of the migrations native types,
       # which is one of the following:
       # <tt>:primary_key</tt>, <tt>:string</tt>, <tt>:text</tt>,
-      # <tt>:integer</tt>, <tt>:bigint</tt>, <tt>:float</tt>, <tt>:decimal</tt>,
+      # <tt>:integer</tt>, <tt>:bigint</tt>, <tt>:float</tt>, <tt>:decimal</tt>, <tt>:numeric</tt>,
       # <tt>:datetime</tt>, <tt>:time</tt>, <tt>:date</tt>,
       # <tt>:binary</tt>, <tt>:boolean</tt>.
       #
@@ -468,9 +477,9 @@ module ActiveRecord
       #   Allows or disallows +NULL+ values in the column. This option could
       #   have been named <tt>:null_allowed</tt>.
       # * <tt>:precision</tt> -
-      #   Specifies the precision for a <tt>:decimal</tt> column.
+      #   Specifies the precision for the <tt>:decimal</tt> and <tt>:numeric</tt> columns.
       # * <tt>:scale</tt> -
-      #   Specifies the scale for a <tt>:decimal</tt> column.
+      #   Specifies the scale for the <tt>:decimal</tt> and <tt>:numeric</tt> columns.
       #
       # Note: The precision is the total number of significant digits
       # and the scale is the number of digits that can be stored following
@@ -487,8 +496,6 @@ module ActiveRecord
       #   Default is (10,0).
       # * PostgreSQL: <tt>:precision</tt> [1..infinity],
       #   <tt>:scale</tt> [0..infinity]. No default.
-      # * SQLite2: Any <tt>:precision</tt> and <tt>:scale</tt> may be used.
-      #   Internal storage as strings. No default.
       # * SQLite3: No restrictions on <tt>:precision</tt> and <tt>:scale</tt>,
       #   but the maximum supported <tt>:precision</tt> is 16. No default.
       # * Oracle: <tt>:precision</tt> [1..38], <tt>:scale</tt> [-84..127].
@@ -691,7 +698,7 @@ module ActiveRecord
       #
       #   CREATE FULLTEXT INDEX index_developers_on_name ON developers (name) -- MySQL
       #
-      # Note: only supported by MySQL. Supported: <tt>:fulltext</tt> and <tt>:spatial</tt> on MyISAM tables.
+      # Note: only supported by MySQL.
       def add_index(table_name, column_name, options = {})
         index_name, index_type, index_columns, index_options = add_index_options(table_name, column_name, options)
         execute "CREATE #{index_type} INDEX #{quote_column_name(index_name)} ON #{quote_table_name(table_name)} (#{index_columns})#{index_options}"
@@ -957,9 +964,9 @@ module ActiveRecord
       def dump_schema_information #:nodoc:
         sm_table = ActiveRecord::Migrator.schema_migrations_table_name
 
-        ActiveRecord::SchemaMigration.order('version').map { |sm|
-          "INSERT INTO #{sm_table} (version) VALUES ('#{sm.version}');"
-        }.join "\n\n"
+        sql = "INSERT INTO #{sm_table} (version) VALUES "
+        sql << ActiveRecord::SchemaMigration.order('version').pluck(:version).map {|v| "('#{v}')" }.join(', ')
+        sql << ";\n\n"
       end
 
       # Should not be called normally, but this operation is non-destructive.
@@ -972,6 +979,10 @@ module ActiveRecord
         ActiveRecord::InternalMetadata.create_table
       end
 
+      def internal_string_options_for_primary_key # :nodoc:
+        { primary_key: true }
+      end
+
       def assume_migrated_upto_version(version, migrations_paths)
         migrations_paths = Array(migrations_paths)
         version = version.to_i
@@ -987,14 +998,12 @@ module ActiveRecord
           execute "INSERT INTO #{sm_table} (version) VALUES ('#{version}')"
         end
 
-        inserted = Set.new
-        (versions - migrated).each do |v|
-          if inserted.include?(v)
-            raise "Duplicate migration #{v}. Please renumber your migrations to resolve the conflict."
-          elsif v < version
-            execute "INSERT INTO #{sm_table} (version) VALUES ('#{v}')"
-            inserted << v
+        inserting = (versions - migrated).select {|v| v < version}
+        if inserting.any?
+          if (duplicate = inserting.detect {|v| inserting.count(v) > 1})
+            raise "Duplicate migration #{duplicate}. Please renumber your migrations to resolve the conflict."
           end
+          execute "INSERT INTO #{sm_table} (version) VALUES #{inserting.map {|v| "('#{v}')"}.join(', ') }"
         end
       end
 
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/transaction.rb b/activerecord/lib/active_record/connection_adapters/abstract/transaction.rb
index 14d04a6388..6ecdab6eb0 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/transaction.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/transaction.rb
@@ -167,8 +167,13 @@ module ActiveRecord
 
       def commit_transaction
         transaction = @stack.last
-        transaction.before_commit_records
-        @stack.pop
+
+        begin
+          transaction.before_commit_records
+        ensure
+          @stack.pop
+        end
+
         transaction.commit
         transaction.commit_records
       end
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
index 3e84786be0..8751b6da4b 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
@@ -1,5 +1,6 @@
 require 'active_record/connection_adapters/abstract_adapter'
 require 'active_record/connection_adapters/mysql/column'
+require 'active_record/connection_adapters/mysql/explain_pretty_printer'
 require 'active_record/connection_adapters/mysql/schema_creation'
 require 'active_record/connection_adapters/mysql/schema_definitions'
 require 'active_record/connection_adapters/mysql/schema_dumper'
@@ -31,12 +32,6 @@ module ActiveRecord
       class_attribute :emulate_booleans
       self.emulate_booleans = true
 
-      LOST_CONNECTION_ERROR_MESSAGES = [
-        "Server shutdown in progress",
-        "Broken pipe",
-        "Lost connection to MySQL server during query",
-        "MySQL server has gone away" ]
-
       QUOTED_TRUE, QUOTED_FALSE = '1', '0'
 
       NATIVE_DATABASE_TYPES = {
@@ -57,7 +52,6 @@ module ActiveRecord
       INDEX_TYPES  = [:fulltext, :spatial]
       INDEX_USINGS = [:btree, :hash]
 
-      # FIXME: Make the first parameter more similar for the two adapters
       def initialize(connection, logger, connection_options, config)
         super(connection, logger, config)
         @quoted_column_names, @quoted_table_names = {}, {}
@@ -70,16 +64,18 @@ module ActiveRecord
         else
           @prepared_statements = false
         end
+
+        if version < '5.0.0'
+          raise "Your version of MySQL (#{full_version.match(/^\d+\.\d+\.\d+/)[0]}) is too old. Active Record supports MySQL >= 5.0."
+        end
       end
 
-      MAX_INDEX_LENGTH_FOR_CHARSETS_OF_4BYTES_MAXLEN = 191
       CHARSETS_OF_4BYTES_MAXLEN = ['utf8mb4', 'utf16', 'utf16le', 'utf32']
-      def initialize_schema_migrations_table
-        if CHARSETS_OF_4BYTES_MAXLEN.include?(charset)
-          ActiveRecord::SchemaMigration.create_table(MAX_INDEX_LENGTH_FOR_CHARSETS_OF_4BYTES_MAXLEN)
-        else
-          ActiveRecord::SchemaMigration.create_table
-        end
+
+      def internal_string_options_for_primary_key # :nodoc:
+        super.tap { |options|
+          options[:collation] = collation.sub(/\A[^_]+/, 'utf8') if CHARSETS_OF_4BYTES_MAXLEN.include?(charset)
+        }
       end
 
       def version
@@ -105,12 +101,8 @@ module ActiveRecord
         true
       end
 
-      # MySQL 4 technically support transaction isolation, but it is affected by a bug
-      # where the transaction level gets persisted for the whole session:
-      #
-      # http://bugs.mysql.com/bug.php?id=39170
       def supports_transaction_isolation?
-        version >= '5.0.0'
+        true
       end
 
       def supports_explain?
@@ -126,17 +118,15 @@ module ActiveRecord
       end
 
       def supports_views?
-        version >= '5.0.0'
+        true
       end
 
       def supports_datetime_with_precision?
         version >= '5.6.4'
       end
 
-      # 5.0.0 definitely supports it, possibly supported by earlier versions but
-      # not sure
       def supports_advisory_locks?
-        version >= '5.0.0'
+        true
       end
 
       def get_advisory_lock(lock_name, timeout = 0) # :nodoc:
@@ -238,72 +228,7 @@ module ActiveRecord
         result  = exec_query(sql, 'EXPLAIN', binds)
         elapsed = Time.now - start
 
-        ExplainPrettyPrinter.new.pp(result, elapsed)
-      end
-
-      class ExplainPrettyPrinter # :nodoc:
-        # Pretty prints the result of an EXPLAIN in a way that resembles the output of the
-        # MySQL shell:
-        #
-        #   +----+-------------+-------+-------+---------------+---------+---------+-------+------+-------------+
-        #   | id | select_type | table | type  | possible_keys | key     | key_len | ref   | rows | Extra       |
-        #   +----+-------------+-------+-------+---------------+---------+---------+-------+------+-------------+
-        #   |  1 | SIMPLE      | users | const | PRIMARY       | PRIMARY | 4       | const |    1 |             |
-        #   |  1 | SIMPLE      | posts | ALL   | NULL          | NULL    | NULL    | NULL  |    1 | Using where |
-        #   +----+-------------+-------+-------+---------------+---------+---------+-------+------+-------------+
-        #   2 rows in set (0.00 sec)
-        #
-        # This is an exercise in Ruby hyperrealism :).
-        def pp(result, elapsed)
-          widths    = compute_column_widths(result)
-          separator = build_separator(widths)
-
-          pp = []
-
-          pp << separator
-          pp << build_cells(result.columns, widths)
-          pp << separator
-
-          result.rows.each do |row|
-            pp << build_cells(row, widths)
-          end
-
-          pp << separator
-          pp << build_footer(result.rows.length, elapsed)
-
-          pp.join("\n") + "\n"
-        end
-
-        private
-
-        def compute_column_widths(result)
-          [].tap do |widths|
-            result.columns.each_with_index do |column, i|
-              cells_in_column = [column] + result.rows.map {|r| r[i].nil? ? 'NULL' : r[i].to_s}
-              widths << cells_in_column.map(&:length).max
-            end
-          end
-        end
-
-        def build_separator(widths)
-          padding = 1
-          '+' + widths.map {|w| '-' * (w + (padding*2))}.join('+') + '+'
-        end
-
-        def build_cells(items, widths)
-          cells = []
-          items.each_with_index do |item, i|
-            item = 'NULL' if item.nil?
-            justifier = item.is_a?(Numeric) ? 'rjust' : 'ljust'
-            cells << item.to_s.send(justifier, widths[i])
-          end
-          '| ' + cells.join(' | ') + ' |'
-        end
-
-        def build_footer(nrows, elapsed)
-          rows_label = nrows == 1 ? 'row' : 'rows'
-          "#{nrows} #{rows_label} in set (%.2f sec)" % elapsed
-        end
+        MySQL::ExplainPrettyPrinter.new.pp(result, elapsed)
       end
 
       def clear_cache!
@@ -980,7 +905,6 @@ module ActiveRecord
         when 3; 'mediumint'
         when nil, 4; 'int'
         when 5..8; 'bigint'
-        when 11; 'int(11)' # backward compatibility with Rails 2.0
         else raise(ActiveRecordError, "No integer type has byte size #{limit}")
         end
       end
diff --git a/activerecord/lib/active_record/connection_adapters/column.rb b/activerecord/lib/active_record/connection_adapters/column.rb
index 81de7c03fb..10f908538f 100644
--- a/activerecord/lib/active_record/connection_adapters/column.rb
+++ b/activerecord/lib/active_record/connection_adapters/column.rb
@@ -30,7 +30,7 @@ module ActiveRecord
       end
 
       def bigint?
-        /bigint/ === sql_type
+        /\Abigint\b/ === sql_type
       end
 
       # Returns the human name of the column name.
diff --git a/activerecord/lib/active_record/connection_adapters/connection_specification.rb b/activerecord/lib/active_record/connection_adapters/connection_specification.rb
index f633892dee..4bc6447368 100644
--- a/activerecord/lib/active_record/connection_adapters/connection_specification.rb
+++ b/activerecord/lib/active_record/connection_adapters/connection_specification.rb
@@ -33,7 +33,7 @@ module ActiveRecord
         def initialize(url)
           raise "Database URL cannot be empty" if url.blank?
           @uri     = uri_parser.parse(url)
-          @adapter = @uri.scheme.tr('-', '_')
+          @adapter = @uri.scheme && @uri.scheme.tr('-', '_')
           @adapter = "postgresql" if @adapter == "postgres"
 
           if @uri.opaque
diff --git a/activerecord/lib/active_record/connection_adapters/mysql/explain_pretty_printer.rb b/activerecord/lib/active_record/connection_adapters/mysql/explain_pretty_printer.rb
new file mode 100644
index 0000000000..1820853196
--- /dev/null
+++ b/activerecord/lib/active_record/connection_adapters/mysql/explain_pretty_printer.rb
@@ -0,0 +1,70 @@
+module ActiveRecord
+  module ConnectionAdapters
+    module MySQL
+      class ExplainPrettyPrinter # :nodoc:
+        # Pretty prints the result of an EXPLAIN in a way that resembles the output of the
+        # MySQL shell:
+        #
+        #   +----+-------------+-------+-------+---------------+---------+---------+-------+------+-------------+
+        #   | id | select_type | table | type  | possible_keys | key     | key_len | ref   | rows | Extra       |
+        #   +----+-------------+-------+-------+---------------+---------+---------+-------+------+-------------+
+        #   |  1 | SIMPLE      | users | const | PRIMARY       | PRIMARY | 4       | const |    1 |             |
+        #   |  1 | SIMPLE      | posts | ALL   | NULL          | NULL    | NULL    | NULL  |    1 | Using where |
+        #   +----+-------------+-------+-------+---------------+---------+---------+-------+------+-------------+
+        #   2 rows in set (0.00 sec)
+        #
+        # This is an exercise in Ruby hyperrealism :).
+        def pp(result, elapsed)
+          widths    = compute_column_widths(result)
+          separator = build_separator(widths)
+
+          pp = []
+
+          pp << separator
+          pp << build_cells(result.columns, widths)
+          pp << separator
+
+          result.rows.each do |row|
+            pp << build_cells(row, widths)
+          end
+
+          pp << separator
+          pp << build_footer(result.rows.length, elapsed)
+
+          pp.join("\n") + "\n"
+        end
+
+        private
+
+        def compute_column_widths(result)
+          [].tap do |widths|
+            result.columns.each_with_index do |column, i|
+              cells_in_column = [column] + result.rows.map {|r| r[i].nil? ? 'NULL' : r[i].to_s}
+              widths << cells_in_column.map(&:length).max
+            end
+          end
+        end
+
+        def build_separator(widths)
+          padding = 1
+          '+' + widths.map {|w| '-' * (w + (padding*2))}.join('+') + '+'
+        end
+
+        def build_cells(items, widths)
+          cells = []
+          items.each_with_index do |item, i|
+            item = 'NULL' if item.nil?
+            justifier = item.is_a?(Numeric) ? 'rjust' : 'ljust'
+            cells << item.to_s.send(justifier, widths[i])
+          end
+          '| ' + cells.join(' | ') + ' |'
+        end
+
+        def build_footer(nrows, elapsed)
+          rows_label = nrows == 1 ? 'row' : 'rows'
+          "#{nrows} #{rows_label} in set (%.2f sec)" % elapsed
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/connection_adapters/mysql/schema_dumper.rb b/activerecord/lib/active_record/connection_adapters/mysql/schema_dumper.rb
index 9dee3172f4..ccf5b6cadc 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql/schema_dumper.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql/schema_dumper.rb
@@ -12,7 +12,7 @@ module ActiveRecord
             spec[:unsigned] = 'true' if column.unsigned?
             return if spec.empty?
           else
-            spec[:id] = column.type.inspect
+            spec[:id] = schema_type(column).inspect
             spec.merge!(prepare_column_options(column).delete_if { |key, _| [:name, :type, :null].include?(key) })
           end
           spec
@@ -32,7 +32,7 @@ module ActiveRecord
 
         def schema_type(column)
           if column.sql_type == 'tinyblob'
-            'blob'
+            :blob
           else
             super
           end
diff --git a/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb b/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb
index c3c5b660fd..23b33a3555 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb
@@ -42,7 +42,7 @@ module ActiveRecord
       end
 
       def supports_json?
-        version >= '5.7.8'
+        !mariadb? && version >= '5.7.8'
       end
 
       # HELPER METHODS ===========================================
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/database_statements.rb b/activerecord/lib/active_record/connection_adapters/postgresql/database_statements.rb
index 6c15facf3b..6aa264d766 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/database_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/database_statements.rb
@@ -4,44 +4,7 @@ module ActiveRecord
       module DatabaseStatements
         def explain(arel, binds = [])
           sql = "EXPLAIN #{to_sql(arel, binds)}"
-          ExplainPrettyPrinter.new.pp(exec_query(sql, 'EXPLAIN', binds))
-        end
-
-        class ExplainPrettyPrinter # :nodoc:
-          # Pretty prints the result of an EXPLAIN in a way that resembles the output of the
-          # PostgreSQL shell:
-          #
-          #                                     QUERY PLAN
-          #   ------------------------------------------------------------------------------
-          #    Nested Loop Left Join  (cost=0.00..37.24 rows=8 width=0)
-          #      Join Filter: (posts.user_id = users.id)
-          #      ->  Index Scan using users_pkey on users  (cost=0.00..8.27 rows=1 width=4)
-          #            Index Cond: (id = 1)
-          #      ->  Seq Scan on posts  (cost=0.00..28.88 rows=8 width=4)
-          #            Filter: (posts.user_id = 1)
-          #   (6 rows)
-          #
-          def pp(result)
-            header = result.columns.first
-            lines  = result.rows.map(&:first)
-
-            # We add 2 because there's one char of padding at both sides, note
-            # the extra hyphens in the example above.
-            width = [header, *lines].map(&:length).max + 2
-
-            pp = []
-
-            pp << header.center(width).rstrip
-            pp << '-' * width
-
-            pp += lines.map {|line| " #{line}"}
-
-            nrows = result.rows.length
-            rows_label = nrows == 1 ? 'row' : 'rows'
-            pp << "(#{nrows} #{rows_label})"
-
-            pp.join("\n") + "\n"
-          end
+          PostgreSQL::ExplainPrettyPrinter.new.pp(exec_query(sql, 'EXPLAIN', binds))
         end
 
         def select_value(arel, name = nil, binds = [])
@@ -128,6 +91,8 @@ module ActiveRecord
 
         # Executes an SQL statement, returning a PGresult object on success
         # or raising a PGError exception otherwise.
+        # Note: the PGresult object is manually memory managed; if you don't
+        # need it specifically, you many want consider the exec_query wrapper.
         def execute(sql, name = nil)
           log(sql, name) do
             @connection.async_exec(sql)
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/explain_pretty_printer.rb b/activerecord/lib/active_record/connection_adapters/postgresql/explain_pretty_printer.rb
new file mode 100644
index 0000000000..789b88912c
--- /dev/null
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/explain_pretty_printer.rb
@@ -0,0 +1,42 @@
+module ActiveRecord
+  module ConnectionAdapters
+    module PostgreSQL
+      class ExplainPrettyPrinter # :nodoc:
+        # Pretty prints the result of an EXPLAIN in a way that resembles the output of the
+        # PostgreSQL shell:
+        #
+        #                                     QUERY PLAN
+        #   ------------------------------------------------------------------------------
+        #    Nested Loop Left Join  (cost=0.00..37.24 rows=8 width=0)
+        #      Join Filter: (posts.user_id = users.id)
+        #      ->  Index Scan using users_pkey on users  (cost=0.00..8.27 rows=1 width=4)
+        #            Index Cond: (id = 1)
+        #      ->  Seq Scan on posts  (cost=0.00..28.88 rows=8 width=4)
+        #            Filter: (posts.user_id = 1)
+        #   (6 rows)
+        #
+        def pp(result)
+          header = result.columns.first
+          lines  = result.rows.map(&:first)
+
+          # We add 2 because there's one char of padding at both sides, note
+          # the extra hyphens in the example above.
+          width = [header, *lines].map(&:length).max + 2
+
+          pp = []
+
+          pp << header.center(width).rstrip
+          pp << '-' * width
+
+          pp += lines.map {|line| " #{line}"}
+
+          nrows = result.rows.length
+          rows_label = nrows == 1 ? 'row' : 'rows'
+          pp << "(#{nrows} #{rows_label})"
+
+          pp.join("\n") + "\n"
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/oid/money.rb b/activerecord/lib/active_record/connection_adapters/postgresql/oid/money.rb
index 2163674019..dcc12ae2a4 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/oid/money.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/oid/money.rb
@@ -3,8 +3,6 @@ module ActiveRecord
     module PostgreSQL
       module OID # :nodoc:
         class Money < Type::Decimal # :nodoc:
-          class_attribute :precision
-
           def type
             :money
           end
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/schema_dumper.rb b/activerecord/lib/active_record/connection_adapters/postgresql/schema_dumper.rb
index cc7721ddd8..b82bdb8b0c 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/schema_dumper.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/schema_dumper.rb
@@ -11,7 +11,7 @@ module ActiveRecord
             spec[:id] = ':uuid'
             spec[:default] = schema_default(column) || 'nil'
           else
-            spec[:id] = column.type.inspect
+            spec[:id] = schema_type(column).inspect
             spec.merge!(prepare_column_options(column).delete_if { |key, _| [:name, :type, :null].include?(key) })
           end
           spec
@@ -35,9 +35,9 @@ module ActiveRecord
           return super unless column.serial?
 
           if column.bigint?
-            'bigserial'
+            :bigserial
           else
-            'serial'
+            :serial
           end
         end
 
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index 2de6fbfaf0..beaeef3c78 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -5,6 +5,7 @@ require 'pg'
 require "active_record/connection_adapters/abstract_adapter"
 require "active_record/connection_adapters/postgresql/column"
 require "active_record/connection_adapters/postgresql/database_statements"
+require "active_record/connection_adapters/postgresql/explain_pretty_printer"
 require "active_record/connection_adapters/postgresql/oid"
 require "active_record/connection_adapters/postgresql/quoting"
 require "active_record/connection_adapters/postgresql/referential_integrity"
@@ -213,8 +214,8 @@ module ActiveRecord
         @statements = StatementPool.new @connection,
                                         self.class.type_cast_config_to_integer(config.fetch(:statement_limit) { 1000 })
 
-        if postgresql_version < 80200
-          raise "Your version of PostgreSQL (#{postgresql_version}) is too old, please upgrade!"
+        if postgresql_version < 90100
+          raise "Your version of PostgreSQL (#{postgresql_version}) is too old. Active Record supports PostgreSQL >= 9.1."
         end
 
         add_pg_decoders
@@ -296,9 +297,8 @@ module ActiveRecord
         true
       end
 
-      # Returns true if pg > 9.1
       def supports_extensions?
-        postgresql_version >= 90100
+        true
       end
 
       # Range datatypes weren't introduced until PostgreSQL 9.2
@@ -645,12 +645,6 @@ module ActiveRecord
         # connected server's characteristics.
         def connect
           @connection = PGconn.connect(@connection_parameters)
-
-          # Money type has a fixed precision of 10 in PostgreSQL 8.2 and below, and as of
-          # PostgreSQL 8.3 it has a fixed precision of 19. PostgreSQLColumn.extract_precision
-          # should know about this but can't detect it there, so deal with it here.
-          OID::Money.precision = (postgresql_version >= 80300) ? 19 : 10
-
           configure_connection
         rescue ::PG::Error => error
           if error.message.include?("does not exist")
diff --git a/activerecord/lib/active_record/connection_adapters/sqlite3/explain_pretty_printer.rb b/activerecord/lib/active_record/connection_adapters/sqlite3/explain_pretty_printer.rb
new file mode 100644
index 0000000000..a946f5ebd0
--- /dev/null
+++ b/activerecord/lib/active_record/connection_adapters/sqlite3/explain_pretty_printer.rb
@@ -0,0 +1,19 @@
+module ActiveRecord
+  module ConnectionAdapters
+    module SQLite3
+      class ExplainPrettyPrinter # :nodoc:
+        # Pretty prints the result of an EXPLAIN QUERY PLAN in a way that resembles
+        # the output of the SQLite shell:
+        #
+        #   0|0|0|SEARCH TABLE users USING INTEGER PRIMARY KEY (rowid=?) (~1 rows)
+        #   0|1|1|SCAN TABLE posts (~100000 rows)
+        #
+        def pp(result)
+          result.rows.map do |row|
+            row.join('|')
+          end.join("\n") + "\n"
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb b/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
index d1893f35f5..c65d33ccb3 100644
--- a/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
@@ -1,5 +1,6 @@
 require 'active_record/connection_adapters/abstract_adapter'
 require 'active_record/connection_adapters/statement_pool'
+require 'active_record/connection_adapters/sqlite3/explain_pretty_printer'
 require 'active_record/connection_adapters/sqlite3/schema_creation'
 
 gem 'sqlite3', '~> 1.3.6'
@@ -7,7 +8,6 @@ require 'sqlite3'
 
 module ActiveRecord
   module ConnectionHandling # :nodoc:
-    # sqlite3 adapter reuses sqlite_connection.
     def sqlite3_connection(config)
       # Require database.
       unless config[:database]
@@ -218,21 +218,7 @@ module ActiveRecord
 
       def explain(arel, binds = [])
         sql = "EXPLAIN QUERY PLAN #{to_sql(arel, binds)}"
-        ExplainPrettyPrinter.new.pp(exec_query(sql, 'EXPLAIN', []))
-      end
-
-      class ExplainPrettyPrinter
-        # Pretty prints the result of an EXPLAIN QUERY PLAN in a way that resembles
-        # the output of the SQLite shell:
-        #
-        #   0|0|0|SEARCH TABLE users USING INTEGER PRIMARY KEY (rowid=?) (~1 rows)
-        #   0|1|1|SCAN TABLE posts (~100000 rows)
-        #
-        def pp(result) # :nodoc:
-          result.rows.map do |row|
-            row.join('|')
-          end.join("\n") + "\n"
-        end
+        SQLite3::ExplainPrettyPrinter.new.pp(exec_query(sql, 'EXPLAIN', []))
       end
 
       def exec_query(sql, name = nil, binds = [], prepare: false)