The default .htaccess file that comes with Magento has several sections dealing with performance. The following configurations are commented out and must be enabled to realize their benefit.

This section will turn on the apache mod_deflate module, which compresses text, css, and javascript before it is sent to the browser. This achieves a smaller download size. To enable, simply uncomment the appropriate lines so that it looks like the following:

############################################## enable apache served files compression## http://developer.yahoo.com/performance/rules.html#gzip    # Insert filter on all content    SetOutputFilter DEFLATE    # Insert filter on selected content types only    AddOutputFilterByType DEFLATE text/html text/plain text/xml text/css text/javascript application/javascript     # Netscape 4.x has some problems...    BrowserMatch ^Mozilla/4 gzip-only-text/html    # Netscape 4.06-4.08 have some more problems    BrowserMatch ^Mozilla/4\.0[678] no-gzip    # MSIE masquerades as Netscape, but it is fine    BrowserMatch \bMSIE !no-gzip !gzip-only-text/html    # Don‘t compress images    SetEnvIfNoCase Request_URI \.(?:gif|jpe?g|png)$ no-gzip dont-vary    # Make sure proxies don‘t deliver the wrong content    Header append Vary User-Agent env=!dont-vary

Browsers use Expires headers to determine how long a page component can be cached. Static components, like images, should have far-future expires headers, but all page components should have expires headers. To activate this feature, uncomment the appropriate line and add ExpiresActive On directly above it:

############################################## Add default Expires header## http://developer.yahoo.com/performance/rules.html#expires    ExpiresActive On    ExpiresDefault "access plus 1 year"

ETags are a way for browsers to validate cached components across subsequent visits. They can slow down a site served from a cluster if the cluster has not implemented them properly. It is best to disable them as follows:

############################################## If running in cluster environment, uncomment this## http://developer.yahoo.com/performance/rules.html#etags    FileETag none

Generally, these features are available on versions 1.4.0.1 and higher and should be performed after completing the majority of developmental tasks.

This feature reduces the number of HTTP requests. For versions earlier than 1.4.x, use the Fooman_Speedster extension instead.

Attention: Combining CSS/JS when using CDN will cause CSS/JS to "break" until the CDN updates completely. Nexcess recommends starting this process at the beginning non-peak hours to allow enough time for the "new" CSS/JS to reach the CDN.

1. In the Magento Admin, select System > Configuration > Developer.
2. Under Javascript Settings, change Merge Javascript Files to YES.
3. Under CSS Settings, change Merge CSS Files to YES.
4. Clear the cache.

Magento uses the EAV model to store customer and product data. This enables these objects to be incredibly extensible, but results in longer SQL queries and more reads. Enabling the Flat Catalog for Categories and Products merges product data into one table, thereby improving performance. Generally, all stores should enable Flat Catalog for Categories. Stores with over 1000 products should enable Flat Catalog for Products.

1. From the Magento administator interface , go to System > Configuration > Catalog.
2. Under Frontend, change "Use Flat Catalog Category" to YES.
3. If desired, under Frontend, change "Use Flat Catalog Product" to YES.
4. Clear the cache.

For details, refer to How to configure the Nexcess CDN with Magento. 

Magento‘s database can quickly become sluggish due to unmaintained log tabes. Refer to Magento Database Maintenance for information regarding database maintenance.