Apache Guide: Logging, Part 4 -- Log-File Analysis

by Rich Bowen

The problem with log files is that they track an enormous amount of information -- not all of it much good to the people that pay your salary.

In the first sections of this series, I've talked about what goes into the standard log files, and how you can change the contents of those files.

This week, we're looking at how to get meaningful information back out of those log files.

The Challenge

The problem is that although there is an enormous amount of information in the log files, it's not much good to the people that pay your salary. They want to know how many people visited your site, what they looked at, how long they stayed, and where they found out about your site. All of that information is (or might be) in your log files.

They also want to know the names, addresses, and shoe sizes of those people, and, hopefully, their credit card numbers. That information is not in there, and you need to know how to explain to your employer that not only is it not in there, but the only way to get this information is to explicitly ask your visitors for this information, and be willing to be told 'no.'

What Your Log Files Can Tell You

There is a lot of information available to put in your log files, including the following:

Address of the remote machine
This is almost the same as "who is visiting my web site," but not quite. More specifically, it tells you where that visitor is from. This will be something like buglet.rcbowen.com or proxy01.aol.com.

Time of visit
When did this person come to my web site? This can tell you something about your visitors. If most of your visits come between the hours of 9 a.m. and 4 p.m., then you're probably getting visits from people at work. If it's mostly 7 p.m. through midnight, people are looking at your site from home.

Single records, of course, give you very little useful information, but across several thousand 'hits', you can start to gather useful statistics.

Resource requested.
What parts of your site are most popular? Those are the parts that you should expand. Which parts of the site are completely neglected? Perhaps those parts of the site are just really hard to get to. Or, perhaps they are genuinely uninteresting, in which case you should spice them up a little. Of course, some parts of your site, such as your legal statements, are boring and there's nothing you can do about it, but they need to stay on the site for the two or three people that want to see them.

What's broken?
And, of course, your logs tell you when things are not working as they should be. Do you have broken links? Do other sites have links to your site that are not correct? Are some of your CGI programs malfunctioning? Is a robot overwhelming your site with thousands of requests per second? (Yes, this has happened to me. In fact, it's the reason that I did not get this article in on time last week!)

What your log files don't tell you

HTTP is a stateless, anonymous protocol. This is by design, and is not, at least in my opinion, a shortcoming of the protocol. If you want to know more about your visitors, you have to be polite, and actually ask them. And be prepared to not get reliable answers. This is amazingly frustrating for marketing types. They want to know the average income, number of kids, and hair color, of their target demographic. Or something like that. And they don't like to be told that that information is not available in the log files. However, it is quite beyond your control to get this information out of the log files. Explain to them that HTTP is anonymous.

And even what the log files do tell you is occasionally suspect. For example, I have numerous entries in my log files indicating that a machine called cache-mtc-am05.proxy.aol.com visited my web site today. I can tell that this is a machine that is on the AOL network. But because of the way that AOL works, this might be one person visiting my site many times, or it might be many people visiting my site one time each. AOL does something called proxying, and you can see from the machine address that it is a proxy server. A proxy server is one that one or more people sit behind. They type an address into their browser. It makes that request to the proxy server. The proxy server gets the page (generating the log file entry on my web site). It then passes that page back to the requesting machine. This means that I never see the request from the originating machine, but only the request from the proxy.

Another implication of this is that if, 10 minutes later, someone else sitting behind that same proxy requests the same page, they don't generate a log file entry at all. They type in the address, and that request goes to the proxy server. The proxy sees the request and thinks "I already have that document in memory. There's no point asking the web site for it again." And so instead of asking my web site for the page, it gives the copy that it already has to the client. So, not only is the address field suspect, but the number of request is also suspect.

So, Um, What Good are These Logs?

It might sound like the data that you receive is so suspect as to be useless. This is in fact not the case. It should just be taken with a grain of salt. The number of hits that your site receives is almost certainly not really the number of visitors that came to your site. But it's a good indication. And it still gives you some useful information. Just don't rely on it for exact numbers.

How Do I Get Useful Statistics?

So, to the real meat of all of this. How do you actually generate statistics from your Web-server logs?

There are two main approaches that you can take here. You can either do it yourself, or you can get one of the existing applications that is available to do it for you.

Unless you have custom log files that don't look anything like the Common log format, you should probably get one of the available apps out there. There are some excellent commercial products, and some really good free ones, so you just need to decide what features you are looking for.

So, without further ado, here's some of the great apps out there that can help you with this task.

The Analog web site (http://www.statslab.cam.ac.uk/~sret1/analog/) claims that about 29 percent of all web sites that use any log analysis tool at all use Analog. They claim that this makes it the most popular log analysis tool in the world. This fascinated me in particular, because until last week, I had never heard of it. I suppose that this is because I was happy with what I was using, and had never really looked for anything else.

The example report, which you can see on the Analog web site, seemed very thorough, and to contain all of the stats that I might want. In addition to the pages and pages of detailed statistics, there was a very useful executive summary, which will probably be the only part that your boss will really care about.

Another log analysis tool that I have been introduced to in the past few months is WebTrends. WebTrends provides astoundingly detailed reports on your log files, giving you all sorts of information that you did not know you could get out of these files. And there are lots of pretty graphs generated in the report.

WebTrends has, in my opinion, two counts against it.

The first is that it is really expensive. You can look up the actual price on their web site. (http://www.webtrends.com/default.htm)

The other is that it is painfully slow. A 50MB log file from one site for which I am responsible (one month's traffic) took about 3 hours to grind through to generate the report. Admittedly, it's doing a heck of a lot of stuff. But, for the sake of comparison, the same log file took about 10 minutes using WWWStat. Some of this is just the difference between Perl's ability to grind through text files and C's ability. But 3 hours seemed a little excessive.

Now that I've mentioned it, WWWStat is the package that I've been using for about 6 years now. It's fast, full-featured, and it's free. What more could you want. You can get it at http://www.ics.uci.edu/pub/websoft/wwwstat/ and there is a companion package (linked from that same page) that generates pretty graphs.

It is very easy to automate WWWStat so that it generates your log statistics every night at midnight, and then generates monthly reports at the end of each month.

It may not be as full-featured as WebTrends, but it has given me all the stats that I've ever needed.

Another fine product from Boutell.com, Wusage is now in version 7. I've used it on and off through the years, and have always been impressed by not only the quality of the software but also the amazing responsiveness of the technical support staff.

You can get Wusage at http://www.boutell.com/wusage/

Or, You Can Do it Yourself

If you want to do your own log parsing and reporting, the best tool for the task is going to be Perl. In fact, Perl's name (Practical Extraction and Report Language) is a tribute to its ability to extract useful information from logs and generate reports. (In reality, the name ''Perl'' came before the expansion of it, but I suppose that does not detract from my point.)

The Apache::ParseLog module, available from your favorite CPAN mirror, makes parsing log files simple, and so takes all the work out of generating useful reports from those logs.

For detailed information about how to use this module, install it and read the documentation. Once you have installed the module, you can get at the documentation by typing perldoc Apache::ParseLog.

Trolling through the source code for WWWStat is another good way to learn about Perl log file parsing.

And that's about it

Not much more to say here. I'm sure that I've missed out someone's favorite log parsing tool, and that's to be expected. There are hundreds of them on the market. It's really a question of how much you want to pay, and what sort of reports you need.

Thanks for Listening

Thanks for reading. Let me know if there are any subjects that you'd like to see articles on in the future. You can contact me at ApacheToday@rcbowen.com


This article was originally published on Monday Sep 18th 2000
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