We recently conducted a performance assessment for a client, and the main problem was something really simple, but also very detrimental to the site.
The site used the Service Links module, version 6.x-2.x.
The following are the performance figures for the site, in seconds, before any tuning.

3.67 http://example.com/product/215
2.64 http://example.com/product/572
68.32 http://example.com/list1
65.11 http://example.com/list2

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By design, the Drupal CAPTCHA module disables page caching for pages it is enabled on.
So if you enable CAPTCHA for user login and/or registration forms, those pages will not be cached. This is often acceptable.
However, if you enable CAPTCHA for comments, and have the comment form visible at the bottom of each node, then a big portion of your site's pages will not be cached in the page cache at all.

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With the "Cloud" being in vogue currently, we see a lot of clients asking for cloud solutions, mostly Amazon AWS. Sadly, this is normally done without really doing a proper evaluation into whether the cost is reasonable, or the technology is suitable for their specific needs.
Amazon AWS provides some unique and compelling features.

In a previous article, we showed how a combination of Microsoft's WebDAV MiniReDir and Drupal Single SignOn result in an unintentional aggressive crawler that has the same effect as a Denial of Service attack (DoS).
And in our session yesterday at DrupalCon we touched on that topic again.
So, in this article we expand on this topic and provide more details.

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One of the nice things about Drupal is its pluggable caching system.

For Drupal, Quicktabs is a useful module that provides helpful user navigation aids for a site. Used properly, it can be of great assistance to users navigating your site.

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This is a presentation done on November 2nd, 2009 for the Kitchener Waterloo Linux Users Group on Linux toolbox for monitoring and performance.
Many tools are discussed, including: top, htop, atop, vmstat, netstat, ntop, vnstat, iostat, strace, systemtap, oprofile, apachetop, MySQL processlist, Munin, Awstats, and Google Analytics.

We have posted before on how to display previous/next thumbnails for image nodes. We also have a module that is basically a Previous/Next API for high volume / high performance sites.
But sometimes you need a simpler solution for regular nodes, just using the node title and a link to it. This article explains how to achieve that for Drupal 6 in one simple function and a few changes to one .tpl.php file.
First, we start off with the code that does the heavy lifting.
In your theme's template.php add the first function from the attached file.

A very large site we manage for a client was upgraded recently from the memcache module version 1.12 to version 1.13.
However, the result was less performance for this server that was humming alone happily with the older version.
The Munin graphs tell it all: look at the change at 12:00 noon.
Here is the CPU graph, showing double the CPU utilization on this sever.

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