asg12.htm

apache技术手册

ADSL/DMT Modems* (downloading)

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1,500-8,000Kbps

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Unknown

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T-1 or DS-1 (Digital Service 1)

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1,500Kbps

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$770&#150;$950

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ISDN

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128Kbps

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$325&#150;$450

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ADSL/DMT Modems* (uploading)

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64-768Kbps

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Unknown

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DS-0 (Digital Service 0)

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56-64Kbps

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$180&#150;$225

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Modem

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29Kbps

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$95&#150;$150</FONT>

</TABLE><P>The Price/Month column doesn't include costs related to leasing the line that connects you to the Internet Service Provider (ISP). Typically, you could approximate costs by figuring that a single voice line is $30/month. 28.8 modems, DS-0, and ADSL/DMT lines* take a single line. Any other service requires multiple lines. An ISDN line requires two lines ($60/month); a DS-1 line requires 24 lines ($720/month); a full DS-3 needs around 672 lines ($20,160/month).

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<P>Dedicated network connections vary in price depending on your geographic location, your distance from the provider, the length of your contract, and other factors. The following sections describe the most common services.

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<FONT SIZE=4 COLOR="#FF0000"><A NAME="I231"></A><A NAME="I232"></A><A NAME="I233"></A><A NAME="I234"></A><A NAME="I235"></A><A NAME="I236"></A><A NAME="I237"></A><A NAME="I238"></A><A NAME="I239"></A><A NAME="I240"></A><A NAME="I241"></A><A NAME="I242"></A><A NAME="I243"></A><A NAME="I244"></A><B>DS-0 (Digital Service 0</B><B>)</B></FONT></CENTER></H6>

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<P>DS-0 service is used to enhance two-wire or four-wire voice or analog data, providing a single transmission channel between the end user and the provider. It can also be used as a dedicated link between two remote office locations.

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<FONT SIZE=4 COLOR="#FF0000"><A NAME="I245"></A><A NAME="I246"></A><A NAME="I247"></A><A NAME="I248"></A><A NAME="I249"></A><A NAME="I250"></A><A NAME="I251"></A><A NAME="I252"></A><A NAME="I253"></A><A NAME="I254"></A><A NAME="I255"></A><A NAME="I256"></A><A NAME="I257"></A><A NAME="I258"></A><B>DS-1 (Digital Service 1</B><B>)</B></FONT></CENTER></H6>

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<P>A DS-1 service has a capacity of 1.544Mbps and can carry up to 24 64Kbps voice-grade signals. This service is also known as a T-1, referring to the &quot;T Carrier&quot; digital communication system.

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<FONT SIZE=4 COLOR="#FF0000"><A NAME="I259"></A><A NAME="I260"></A><A NAME="I261"></A><A NAME="I262"></A><A NAME="I263"></A><A NAME="I264"></A><A NAME="I265"></A><A NAME="I266"></A><A NAME="I267"></A><A NAME="I268"></A><A NAME="I269"></A><A NAME="I270"></A><A NAME="I271"></A><A NAME="I272"></A><B>DS-3</B><B> (Digital Service 3</B><B>)</B></FONT></CENTER></H6>

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<P>A DS-3 circuit has the capacity of 44.736Mbps. It is the equivalent of 28 DS-1 circuits, having a capacity of 672 voice-grade signals. This service is also known as a T-3. This is a very high-capacity service.

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<FONT SIZE=4 COLOR="#FF0000"><A NAME="I273"></A><A NAME="I274"></A><A NAME="I275"></A><A NAME="I276"></A><A NAME="I277"></A><A NAME="I278"></A><A NAME="I279"></A><A NAME="I280"></A><A NAME="I281"></A><A NAME="I282"></A><A NAME="I283"></A><A NAME="I284"></A><A NAME="I285"></A><B>Discrete Multitone Asymmetrical Digital Subscriber Line</B><B> (ADSL)</B></FONT></CENTER></H6>

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<P>New technology, such as Discrete Multitone ADSL, promises to deliver incredible performance inexpensively. The technology, intended for consumer Internet access, has varying rates of bandwidth depending on the direction of the transfer. Downloads that operate from DS-1 to almost Ethernet speeds are sure to be hot with consumers. Uploads range from 64Kbps to half of a DS-1 line&#151;respectable performance, considering that it operates over existing copper lines.

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<FONT SIZE=4 COLOR="#FF0000"><A NAME="I286"></A><A NAME="I287"></A><A NAME="I288"></A><A NAME="I289"></A><A NAME="I290"></A><A NAME="I291"></A><A NAME="I292"></A><A NAME="I293"></A><A NAME="I294"></A><A NAME="I295"></A><B>ISDN: Integrated Services Digital Network</B></FONT></CENTER></H6>

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<P>ISDN is a service that allows the combination of voice and data connections over a single high-speed connection. The quality of the voice line is better than the standard voice line because the service is digital. This service works over existing copper wires and requires a modem-like device. The typical consumer ISDN modem costs around $300.

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<FONT SIZE=4 COLOR="#FF0000"><B>Local Networks: Ethernet LANs</B></FONT></CENTER></H5>

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<P>The type of LAN you implement on your network will greatly affect the performance and reliability of your server.

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<P>An Ethernet network is a well-behaved, polite group of computers. If one talks, the others listen. However, that means that the more systems there are on the wire, the more time computers are going to spend waiting to talk. If two talk at the same time, a packet collision occurs. On detecting a collision, all computers will randomly reset their talk interval to avoid a <I>deadlock</I>, which is a condition where the collision continues to occur due to a predetermined silence period.

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<P>One way to improve performance is to have a faster Ethernet. The faster the network, the quicker the packets travel and the more opportunity each system has to talk and deliver its message. Ethernet LANs come in two flavors: 10Mbps and 100Mbps.

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<P>In contrast to most WAN interfaces, Ethernet networks are very fast. However, Ethernet network capacity is only 60 to 80 percent of the rated bandwidth. On a 10Mbps Ethernet network, a server responding to 100 requests per second, each request having an average size of 7KB, is using roughly 60 percent of the available bandwidth. A network experiencing this sort of activity should have a 100Mbps Ethernet backbone support.

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<FONT SIZE=5 COLOR="#FF0000"><B>Software Tuning</B></FONT></CENTER></H3>

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<P>Software tuning will allow your system to operate optimally given a load. There are several configuration details that will make your system more efficient; they are detailed in the following sections.

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<FONT SIZE=4 COLOR="#FF0000"><B>HTTP Server</B></FONT></CENTER></H4>

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<P>The HTTP server software is critical. The Apache server in its default configuration is already tuned very well. Apache provides you with configuration directives that allow you address just about every issue that could affect the performance of your server. These directives cover issues relating to the life of the HTTP children processes, the maximum and minimum number of processes the server runs, whether to enable server-side includes or per-directory access control files, and so on. Configurability is one of the big strengths of the Apache server. If the server does it, you can configure it.

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<P>You will achieve maximum performance for your HTTP server by following these tips:

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<LI>Run a standalone server. The overhead of starting a server under inetd just won't work for any sort of real traffic.

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<LI><A NAME="I296"></A>Don't log anything unless you need to. Logging takes time and resources. If you need to log, you might want to consider some of the special logging options that Apache provides. Configurable logging is one way of building audit trails that are important.

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<LI><A NAME="I297"></A>If you log, don't force the DNS lookups. Requesting reverse DNS lookups takes extra work from the server. Don't use them unless you really need them. Also, log into a different disk (not just a different partition). This will allow the server to access files and write the log files almost concurrently, almost always yielding a performance enhancement for servers that do some logging.

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<LI>Server Side Includes. In a word: <I>Don't</I>! Server Side Includes (SSI) increase disk access. In order to return a requested page, the server has to parse the SSI page, perform some computations, and then return results to the client. How much this increased disk access matters depends on the type of SSI you have. Including big files won't affect your server much, but including many small files will result in several disk accesses. If your SSI includes a header and a footer, that alone accounts for three accesses. In that same amount of time, your server could have returned the same three documents to three separate clients. Consider instead having a script that adds header and footer information to a static HTML file. The script would run under cron every so often and produce a page that the server can return without preprocessing it. Needless to say, an SSI which also makes a CGI call, is twice as expensive.

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<LI>Per-directory access control files generate a lot of server load because the server looks for an .htaccess file in every directory in the path of a request, which can be very painful for deeply-nested requests. As an alternative, consider putting any access restrictions in the global-access control file, conf/access.conf.

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<LI><A NAME="I298"></A>Don't let httpd processes expire too soon. Although it does provide some benefit in terms of memory use to expire the processes every so often (some unices, notably Solaris, leak memory in some of the libraries, making a more frequent process expiration a must), that benefit comes at a cost: a new process needs to be forked to replace the old one. Forking is expensive, especially when your server is under heavy load.

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