This map has a 'text' layer pointed at 'db2text.php', a script which queries the database example.db and generates text in the format OpenLayers can use to display lots of markers (see the generated text)

In this case OpenLayers makes a single request, and db2text.php simply fetches every point from the database, which takes a little while at the server-side. The amount of data returned can also overload your browser a bit. These difficulties are takled with the BBOX strategy example.