The usage of most adapters is pretty straight-forward. However, the database adapters require a more detailed explanation regarding the retrieval and count of the data from the database.
To use the DbSelect and DbTableSelect adapters you don't have to retrieve the data
upfront from the database. Both adapters do the retrieval for you, aswell as the
counting of the total pages. If additional work has to be done on the database results
getItems() method has to be extended in your
Additionally these adapters do not fetch all records from the
database in order to count them. Instead, the adapters manipulates the original query to
produce the corresponding COUNT query. Paginator then executes that COUNT query to get
the number of rows. This does require an extra round-trip to the database, but this is
many times faster than fetching an entire result set and using
count(). Especially with large collections of data.
The database adapters will try and build the most efficient query that will execute on pretty much all modern databases. However, depending on your database or even your own schema setup, there might be more efficient ways to get a rowcount. For this scenario the database adapters allow you to set a custom COUNT query. For example, if you keep track of the count of blog posts in a separate table, you could achieve a faster count query with the following setup:
$adapter = new Zend_Paginator_Adapter_DbSelect($db->select()->from('posts'));
Zend_Paginator_Adapter_DbSelect::ROW_COUNT_COLUMN => 'post_count'
$paginator = new Zend_Paginator($adapter);
This approach will probably not give you a huge performance gain on small collections and/or simple select queries. However, with complex queries and large collections, a similar approach could give you a significant performance boost.