Free MySQL::Result objects after a call to execute [#1416 state:resolved]

No freeing Result objects causes the MySQL driver to free result sets
at undefined times, this can lead to erratic performance in your
application.

Signed-off-by: Frederick Cheung <frederick.cheung@gmail.com>

activerecord/lib/active_record/connection_adapters/mysql_adapter.rb

@@ -308,6 +308,7 @@ def select_rows(sql, name = nil)
         rows
       end
 
+      # Executes a SQL query and returns a MySQL::Result object. Note that you have to free the Result object after you're done using it.
       def execute(sql, name = nil) #:nodoc:
         log(sql, name) { @connection.query(sql) }
       rescue ActiveRecord::StatementInvalid => exception
@@ -414,7 +415,9 @@ def collation
 
       def tables(name = nil) #:nodoc:
         tables = []
-        execute("SHOW TABLES", name).each { |field| tables << field[0] }
+        result = execute("SHOW TABLES", name)
+        result.each { |field| tables << field[0] }
+        result.free
         tables
       end
 
@@ -425,7 +428,8 @@ def drop_table(table_name, options = {})
       def indexes(table_name, name = nil)#:nodoc:
         indexes = []
         current_index = nil
-        execute("SHOW KEYS FROM #{quote_table_name(table_name)}", name).each do |row|
+        result = execute("SHOW KEYS FROM #{quote_table_name(table_name)}", name)
+        result.each do |row|
           if current_index != row[2]
             next if row[2] == "PRIMARY" # skip the primary key
             current_index = row[2]
@@ -434,13 +438,16 @@ def indexes(table_name, name = nil)#:nodoc:
 
           indexes.last.columns << row[4]
         end
+        result.free
         indexes
       end
 
       def columns(table_name, name = nil)#:nodoc:
         sql = "SHOW FIELDS FROM #{quote_table_name(table_name)}"
         columns = []
-        execute(sql, name).each { |field| columns << MysqlColumn.new(field[0], field[4], field[1], field[2] == "YES") }
+        result = execute(sql, name)
+        result.each { |field| columns << MysqlColumn.new(field[0], field[4], field[1], field[2] == "YES") }
+        result.free
         columns
       end
 
@@ -521,9 +528,11 @@ def show_variable(name)
       # Returns a table's primary key and belonging sequence.
       def pk_and_sequence_for(table) #:nodoc:
         keys = []
-        execute("describe #{quote_table_name(table)}").each_hash do |h|
+        result = execute("describe #{quote_table_name(table)}")
+        result.each_hash do |h|
           keys << h["Field"]if h["Key"] == "PRI"
         end
+        result.free
         keys.length == 1 ? [keys.first, nil] : nil
       end