Update overview.md

overview.md

@@ -12,10 +12,12 @@ of a "database" or "schema." It's an abstraction of the interface and existence
 of a database, which might be as varied as a local file, accessed through a network
 connection, or in-memory and in-process.
 
-`sql.DB` performs some important tasks for you behind the scenes:
-
-* It opens and closes connections to the actual underlying database, via the driver.
-* It manages a pool of connections as needed, which may be a variety of things as mentioned.
+`sql.DB` differs from equivalent entity in C#, Java or PHP. It creates a handle with empty slice of connections.
+Subsequent DB operation (Query, QueryRow, Execute, Ping) creates real conection and pushes it into the slice. The connection 
+is marked as 'free' after finishing an operation and subsequent one can reuse it instead of creating new connection.
+Query is finished after closing 'Rows'. QueryRow, Execute or Ping closes connection immediately. DB object allows some
+optimization of the pool calling functions SetMaxOpenConns(), SetMaxIdleConns() and SetConnMaxLifetime(). Details of the optimization are described 
+on site 'https://www.alexedwards.net/blog/configuring-sqldb'.
 
 The `sql.DB` abstraction is designed to keep you from worrying about how to
 manage concurrent access to the underlying datastore.  A connection is marked