O Guia Definitivo do Yii 1.1

As described in the Caching section, Yii provides several caching solutions that may
improve the performance of a Web application significantly. If the generation of some data
takes long time, we can use the data caching approach to reduce the data generation
frequency; If a portion of page remains relatively static, we can use the fragment caching
approach to reduce its rendering frequency; If a whole page remains relative static, we can
use the page caching approach to save the rendering cost for the whole page.
If the application is using Active Record, we should turn on the schema caching to save
the time of parsing database schema. This can be done by configuring the
CDbConnection::schemaCachingDuration property to be a value greater than 0.
Besides these application-level caching techniques, we can also use server-level caching
solutions to boost the application performance. As a matter of fact, the APC caching we
described earlier belongs to this category. There are other server techniques, such as
Zend Optimizer, eAccelerator, Squid, to name a few.
Database Optimization
Fetching data from database is often the main performance bottleneck in a Web
application. Although using caching may alleviate the performance hit, it does not fully
solve the problem. When the database contains enormous data and the cached data is
invalid, fetching the latest data could be prohibitively expensive without proper database
and query design.
Design index wisely in a database. Indexing can make SELECT queries much faster, but it
may slow downINSERT, UPDATE or DELETE queries.
For complex queries, it is recommended to create a database view for it instead of issuing
the queries inside the PHP code and asking DBMS to parse them repetitively.
Do not overuse Active Record. Although Active Record is good at modeling data in an
OOP fashion, it actually degrades performance due to the fact that it needs to create one
or several objects to represent each row of query result. For data intensive applications,
using DAO or database APIs at lower level could be a better choice.
Last but not least, use LIMIT in your SELECT queries. This avoids fetching overwhelming
data from database and exhausting the memory allocated to PHP.
Minimizing Script Files
Complex pages often need to include many external JavaScript and CSS files. Because
each file would cause one extra round trip to the server and back, we should minimize the
number of script files by merging them into fewer ones. We should also consider reducing
the size of each script file to reduce the network transmission time. There are many tools
around to help on these two aspects.
For a page generated by Yii, chances are that some script files are rendered by
components that we do not want to modify (e.g. Yii core components, third-party
components). In order to minimizing these script files, we need two steps.