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Botnet hammering web site causing outages

We had a site for a client that was stable for close to two years, then suddenly started to experience switches from the master to the geographically separate slave server as frequently as twice a week.

The site is an entertainment news site, and its articles get to Google News on occasions.

The symptoms was increased load on the server, a sudden influx of traffic causing over 800 simultaneous connections all in the ESTABLISHED state.

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Overcoming long Views rendering time on Drupal sites

A client contacted us to assist them in finding a solution for slow page times for their site.

All the pages of the site were slow, and taking 2.9 to 3.3 seconds.

Upon investigation, we found that one view was responsible for most of that time.

However, the query execution itself was fast, around 11 ms.

But, the views rendering time was obscenely high: 2,603.48 ms!

So, when editing the view, you would see this at the bottom:

Query build time        2.07 ms
Query execute time     11.32 ms
View render time    2,603.48 ms

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Google Crawler hitting your site too aggressively?

If your Drupal site suffers occasional slow downs or outages, check if crawlers are hitting your site too hard.

We've seen several clients complain, and upon investigation we found that the culprit is Google's own crawler.

The tell tale sign is that you will see lots of queries executing with the LIMIT clause having high numbers. Depending on your site's specifics, these queries would be slow queries too.

This means that there are crawlers that accessing very old content (hundreds of pages back).

Here is an example from a recent client:

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Avoid excessive disk writes by avoiding PHP errors in your code

Recently a client complained that their site has been suffering from slow downs that were not there before.

Upon investigating the history of resource utilization, we found that memory usage has increased, and at the same time, the load average has increased as well.

To cut a long story short, we found out that initially, the site had neither dblog nor syslog modules were enabled, and they were enabled before the issues started. They started when syslog was enabled.

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Presentation: Drupal Camp Toronto 2011 Web Site Performance Optimization and Scalability

Together with Alan Dixon of Black Fly Solutions, Khalid Baheyeldin of 2bits.com, Inc. gave a presentation on Web Site Performance, Optimization and Scalability at Drupal Camp 2011.

The slides from the presentation are attached below.

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Remember that the CAPTCHA module disables page caching

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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Do not configure the Service Links module with TinyURL.com

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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How Google and Bing crawlers were confused by quicktabs

Quick Tabs is a widely used Drupal module. Site builders like it because it improves usability in some cases by reducing clutter.

Incidentally, the way this module works has cause us to run across performance issues caused by certain uses. See previous article about Quick Tabs can sure use more caching and a case study involving Quick Tabs.

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Bypassing Drupal core Node Access table joins to avoid outage caused by slow queries

A client site was facing intermittent outages, specially at peak hours.

We investigated the issue over a few days, and narrowed down the cause to certain slow queries, described in more details below.

They had tagadelic on every page, displaying a tag cloud, and from that, crawlers hit every term to paths like taxonomy/term/1581.

Slow queries causing server outage

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