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Posted to docs-cvs@perl.apache.org by st...@apache.org on 2005/04/11 18:52:34 UTC
svn commit: r160925 -
perl/modperl/docs/trunk/src/docs/tutorials/client/compression/compression.pod
Author: stas
Date: Mon Apr 11 09:52:33 2005
New Revision: 160925
URL: http://svn.apache.org/viewcvs?view=rev&rev=160925
Log:
new version
by Slava Bizyayev <sb...@outlook.net>
Modified:
perl/modperl/docs/trunk/src/docs/tutorials/client/compression/compression.pod
Modified: perl/modperl/docs/trunk/src/docs/tutorials/client/compression/compression.pod
URL: http://svn.apache.org/viewcvs/perl/modperl/docs/trunk/src/docs/tutorials/client/compression/compression.pod?view=diff&r1=160924&r2=160925
==============================================================================
--- perl/modperl/docs/trunk/src/docs/tutorials/client/compression/compression.pod (original)
+++ perl/modperl/docs/trunk/src/docs/tutorials/client/compression/compression.pod Mon Apr 11 09:52:33 2005
@@ -2,43 +2,34 @@
Web Content Compression FAQ
+=head1 Description
+
+Everything you wanted to know about web content compression
+
=head1 Basics of Content Compression
-Compression of outgoing traffic from web servers is beneficial for
-clients who get quicker responses, as well as for providers who experience
-less consumption of bandwidth.
-
-Recently content compression for web servers has been provided mainly through use of the gzip format.
-Other (non perl) modules are available that provide
-so-called C<deflate> compression.
-Both approaches are currently very similar and use the LZ77 algorithm
-combined with Huffman coding.
-Luckily for us, there is no real need to understand all the details
-of the obscure underlying mathematics in order to compress
-outbound content.
-Apache handlers available from CPAN can usually do the dirty work for us.
-Content compression is addressed through
-the proper configuration of appropriate handlers in the httpd.conf file.
+Compression of outbound Web server traffic provides benefits both for Web clients who see shorter response times, as well as for content providers, who experience lower consumption of bandwidth.
-Compression by its nature is a content filter:
+Most recently, content compression for web servers has been provided mainly through use of the C<gzip> encoding.
+Other (non perl) modules are available that provide so-called C<deflate> compression.
+Both approaches are very similar recently and use the LZ77 algorithm combined with Huffman coding.
+Luckily for us, to make use of them, there is no real need for most of us to understand
+all the details of the obscure underlying mathematics of these techniques.
+Apache handlers available from CPAN can usually do the dirty work.
+Apache addresses content compression through handlers configured in its configuration file.
+
+Compression is, by its nature, a content filter:
It always takes its input as plain ASCII data that it converts
-to another C<binary> form and outputs the result to some destination.
-That's why every content compression handler usually belongs
-to a particular chain of handlers within the content generation phase
-of the request-processing flow.
-
-A chain of handlers is one more common term that is good to know about
-when you plan to compress data.
-There are two of them recently developed for Apache 1.3.X:
-C<Apache::OutputChain> and C<Apache::Filter>.
-We have to keep in mind
-that the compression handler developed for one chain usually fails
-inside another.
-
-Another important point deals with the order of execution of handlers
-in a particular chain.
-It's pretty straightforward in C<Apache::Filter>.
-For example, when you configure
+to another C<binary> form, and outputs the result to some destination.
+That is why every content compression handler usually belongs to a particular chain of handlers
+within the content generation phase of the request-processing flow.
+
+A C<chain of handlers> is one more common term that is good to know about when you plan to compress data.
+There are two of them recently developed for Apache 1.3: C<Apache::OutputChain> and C<Apache::Filter>.
+We have to keep in mind that the compression handler developed for one chain usually fails inside another.
+
+Another important point deals with the order of execution of handlers in a particular chain.
+It's pretty straightforward in C<Apache::Filter>. For example, when you configure...
PerlModule Apache::Filter
<Files ~ "*\.blah">
@@ -47,12 +38,10 @@
PerlHandler Filter1 Filter2 Filter3
</Files>
-the content will go through C<Filter1> first,
-then the result will be filtered by C<Filter2>,
-and finally C<Filter3> will be invoked to make the final changes
-in outgoing data.
+...the content will go through C<Filter1> first, then the result will be filtered by C<Filter2>,
+and finally C<Filter3> will be invoked to make the final changes in outbound data.
-However, when you configure
+However, when you configure C<Apache::OutputChain> like...
PerlModule Apache::OutputChain
PerlModule Apache::GzipChain
@@ -63,121 +52,104 @@
PerlHandler Apache::OutputChain Apache::GzipChain Apache::SSIChain Apache::PassHtml
</Files>
-execution begins with C<Apache::PassHtml>.
-Then the content will be processed with C<Apache::SSIChain>
-and finally with C<Apache::GzipChain>.
-C<Apache::OutputChain> will not be involved in content processing at all.
+...execution begins with C<Apache::PassHtml>. Then the content will be processed with C<Apache::SSIChain>
+and finally with C<Apache::GzipChain>. C<Apache::OutputChain> will not be involved in content processing at all.
It is there only for the purpose of joining other handlers within the chain.
-It is important to remember that the content compression handler
-should always be the last executable handler in any chain.
+It is important to remember that the content compression handler should always be the last executable handler in any chain.
-Another important problem of practical implementation
-of web content compression deals with the fact
-that some buggy web clients declare the ability to receive
-and decompress gzipped data in their HTTP requests,
+Another important problem of practical implementation of web content compression deals with the fact
+that some buggy Web clients declare the ability to receive and decompress gzipped data in their HTTP requests,
but fail to keep their promises when an actual compressed response arrives.
-This problem is addressed through the implementation of
-the C<Apache::CompressClientFixup> handler.
+This problem is addressed through the implementation of the C<Apache::CompressClientFixup> handler.
This handler serves the C<fixup> phase of the request-processing flow.
It is compatible with all known compression handlers and is available from CPAN.
-=head1 Q: Why it is important to compress web content?
+=head1 Q: Why it is important to compress Web content?
-=head2 A: Reduced equipment costs and the competitive advantage of
-dramatically faster page loads.
+=head2 A: Reduced equipment costs and the competitive advantage of dramatically faster page loads.
Web content compression noticeably increases delivery speed to clients
-and may allow providers to serve higher content volumes without
-increasing hardware expenditures. It visibly reduces actual content
-download time, a benefit most apparent to users of dialup and
-high-traffic connections.
+and may allow providers to serve higher content volumes without increasing hardware expenditures.
+It visibly reduces actual content download time, a benefit most apparent to users of dialup and high-traffic connections.
+
+Industry leaders like I<Yahoo> and I<Google> are widely using content compression in their businesses.
=head1 Q: How much improvement can I expect?
-=head2 A: Effective compression can achieve increases in transmission
-efficiency from 3 to 20 times.
+=head2 A: Effective compression can achieve increases in transmission efficiency from 3 to 20 times.
-The compression ratio is highly content-dependent. For example, if
-the compression algorithm is able to detect repeated patterns of
-characters, compression will be greater than if no such patterns
-exist. You can usually expect to realize an improvement between of 3
-to 20 times on regular HTML, JavaScript, and other ASCII content. I
-have seen peak HTML file compression improvements in excess of more
-than 200 times, but such occurrences are infrequent. On the other
-hand I have never seen ratios of less than 2.5 times on text/HTML
-files. Image files normally employ their own compression techniques
-that reduce the advantage of further compression.
+The compression ratio is highly content-dependent.
+For example, if the compression algorithm is able to detect repeated patterns of characters,
+compression will be greater than if no such patterns exist.
+You can usually expect to realize an improvement between of 3 to 20 times on regular HTML,
+JavaScript, and other ASCII content.
+I have seen peak HTML file compression improvements in excess of more than 200 times,
+but such occurrences are infrequent.
+On the other hand I have never seen ratios of less than 2.5 times on text/HTML files.
+Image files normally employ their own compression techniques that reduce the advantage of further compression.
=for html
<blockquote>
-On May 21, 2002 Peter J. Cranstone wrote to the
-mod_gzip@lists.over.net mailing list:
+On May 21, 2002 Peter J. Cranstone wrote to the mod_gzip@lists.over.net mailing list:
-I<"...With 98% of the world on a dial up modem, all they care about is
-how long it takes to download a page. It doesn't matter if it
-consumes a few more CPU cycles if the customer is happy. It's cheaper
-to buy a newer faster box, than it is to acquire new customers.">
+I<"...With 98% of the world on a dial up modem, all they care about is how long it takes to download a page. It doesn't matter if it consumes a few more CPU cycles if the customer is happy. It's cheaper to buy a newer faster box, than it is to acquire new customers.">
=for html
</blockquote>
=head1 Q: How hard is it to implement content compression on an existing site?
-=head2 A: Implementing content compression on an existing site
-typically involves no more than installing and configuring an
-appropriate Apache handler on the web server.
-
-This approach works in most of the cases I have seen. In some special
-cases you will need to take extra care with respect to the global
-architecture of your web application, but such cases may generally be
-readily addressed through various techniques. To date I have found no
-fundamental barriers to practical implementation of web content
-compression.
+=head2 A: Implementing content compression on an existing site typically involves no more than installing and configuring an appropriate Apache handler on the Web server.
+
+This approach works in most of the cases I have seen.
+In some special cases you will need to take extra care with respect to the global architecture of your Web application,
+but such cases may generally be readily addressed through various techniques.
+To date I have found no fundamental barriers to practical implementation of Web content compression.
-=head1 Q: Does compression work with standard web browsers?
+=head1 Q: Does compression work with standard Web browsers?
=head2 A: Yes. No client side changes or settings are required.
-All modern browser makers claim to be able to handle compressed
-content and are able to decompress it on the fly, transparent to the
-user. There are some known bugs in some old browsers, but these can
-be taken into account through appropriate configuration of the web
-server.
-
-I strongly recommend use of the C<Apache::CompressClientFixup> handler
-in your server configuration in order to prevent compression
-for known buggy clients.
+All modern browser makers claim to be able to handle compressed content and are able to decompress it on the fly,
+transparent to the user.
+There are some known bugs in some old browsers, but these can be taken into account
+through appropriate configuration of the Web server.
+
+I strongly recommend use of the C<Apache::CompressClientFixup> handler in your server configuration
+in order to prevent compression for known buggy clients.
-=head1 Q: What software is required on the server side?
+=head1 Q: Is it possible to combine the content compression with data encryption?
-=head2 A: There are four known mod_perl modules/packages for the web content
-compression available to date for Apache 1.3.X (in alphabetical order):
+=head2 A: Yes. Compressed content can be encrypted and securely transmitted over SSL.
+
+On the client side, the browser transparently unencrypts and uncompresses the content for the user.
+It is important to maintain the correct order of operations on server side to keep the transaction secure.
+You must compress the content first and then apply an encryption mechanism.
+This is the only order of operations current browsers support.
+
+=head1 Q: What software is required on the server side for content compression?
+
+=head2 A: There are four known mod_perl modules/packages for Web content compression available to date for Apache 1.3 (in alphabetical order):
=over 4
=item * Apache::Compress
-a mod_perl handler developed by Ken Williams (U.S.).
-C<Apache::Compress> is capable to gzip
-output through C<Apache::Filter>.
-This module accumulates all incoming data and then compresses
-the whole content body at once.
+a mod_perl handler developed by Ken Williams (U.S.), C<Apache::Compress>,
+can generate gzip output through the C<Apache::Filter>.
+This module accumulates all incoming data and compresses the entire content body as a unit.
=item * Apache::Dynagzip
-a mod_perl handler, developed by Slava Bizyayev -- a
-Russian programmer residing in the U.S.
-C<Apache::Dynagzip> uses the gzip format to compress
-output through the C<Apache::Filter> or through the internal
-Unix pipe.
-
-C<Apache::Dynagzip> is most useful when one needs to compress dynamic
-outbound web content (generated on the fly from databases, XML, etc.)
-when content length is not known at the time of the request.
+a mod_perl handler developed by Slava Bizyayev, C<Apache::Dynagzip> uses the gzip format
+to compress output dynamically through the C<Apache::Filter> or through the internal Unix pipe.
-C<Apache::Dynagzip>'s features include:
+C<Apache::Dynagzip> is most useful when one needs to compress dynamic outbound Web content
+(generated on the fly from databases, XML, etc.) when content length is not known at the time of the request.
+
+C<Apache::Dynagzip>'s features include:
=over 4
@@ -187,52 +159,61 @@
=item * Support for Perl, Java, or C/C++ CGI applications.
-=item * Advanced control over the proxy cache with the
-configurable C<Vary> HTTP header.
+=item * Advanced control over the proxy cache with the configurable C<Vary> HTTP header.
-=item * Optional control over content lifetime in the client's local
-cache with the configurable C<Expires> HTTP header.
+=item * Optional control over content lifetime in the client's local cache with the configurable C<Expires> HTTP header.
-=item * Optional support for server-side caching of the dynamically
-generated (and compressed) content.
+=item * Optional support for server-side caching of the dynamically generated (and compressed) content.
=item * Optional extra-light compression
-removal of leading blank spaces and/or blank lines,
-which works for all browsers,
+removal of leading blank spaces and/or blank lines, which works for all browsers,
including older ones that cannot uncompress gzip format.
=back
-
=item * Apache::Gzip
-an example of mod_perl filter developed by Lincoln Stein and Doug
-MacEachern for their book I<Writing Apache Modules with Perl and C>
-(U.S.), which like C<Apache::Compress> works through C<Apache::Filter>.
+an example of the mod_perl filter developed by Lincoln Stein and Doug MacEachern
+for their book I<Writing Apache Modules with Perl and C> (U.S.),
+which like C<Apache::Compress> works through C<Apache::Filter>.
C<Apache::Gzip> is not available from CPAN.
-The source code may be found on the book's companion web site at
-L<http://www.modperl.com/>
+The source code may be found on the book's companion Web site at L<http://www.modperl.com/>
=item * Apache::GzipChain
-a mod_perl handler developed by Andreas Koenig (Germany), which
-compresses output through C<Apache::OutputChain> using the gzip format.
+a mod_perl handler developed by Andreas Koenig (Germany),
+which compresses output through C<Apache::OutputChain> using the gzip format.
C<Apache::GzipChain> currently provides in-memory compression only.
-Using this module under C<perl-5.8> or higher is appropriate for Unicode data.
-UTF-8 data passed to C<Compress::Zlib::memGzip()> are converted to raw
-UTF-8 before compression takes place.
+Use of this module under C<perl-5.8> or higher is appropriate for Unicode data.
+UTF-8 data passed to C<Compress::Zlib::memGzip()> are converted to raw UTF-8 before compression takes place.
Other data are simply passed through.
=back
-=head1 Q: Is it possible to compress the output from C<Apache::Registry>
-with C<Apache::Dynagzip>?
+=head1 Q: What is the typical overhead in terms of CPU use for the content compression?
+
+=head2 A: Typical CPU overhead that originates from content compression is insignificant.
-=head2 A: Yes, it is supposed to be pretty easy:
+In my observations of data compression of files of up to 200K it takes less then 60 ms CPU on a P4 3 GHz processor.
+I could not measure the lower boundary reliably for dynamic compression, because there are no really measurable latency.
+From the perspective of global architecture and scalability planning,
+I would suggest allowing some 10 ms per request on I<regular> Web pages
+in order to roughly estimate/predict the performance of the application server.
-If your page/application is initially configured like
+Estimation of connection times is an even less exact matter for of a variety of possible network-related reasons.
+The worst-case scenario is pretty impressive: a slow dialup connection through an ISP with no proxy/buffering
+holds the provider's socket for a time interval proportionate to the size of the requested file.
+At present, gzip reduces this connection time by a factor of approximately 3-20.
+If the ISP buffers its traffic, however, the content provider might not feel a dramatic impact -- apart of the fact
+that they are paying their telecom providers for the transmission of considerable unnecessary data.
+
+=head1 Q: Is it possible to compress the output from C<Apache::Registry> with C<Apache::Dynagzip>?
+
+=head2 A: Yes. This should be fairly easy to accomplish, as follows:
+
+If your page/application is initially configured like this:
<Directory /path/to/subdirectory>
SetHandler perl-script
@@ -241,7 +222,7 @@
Options +ExecCGI
</Directory>
-you might want just to replace it with the following:
+you might replace it with the following:
PerlModule Apache::Filter
PerlModule Apache::Dynagzip
@@ -256,24 +237,23 @@
PerlSetVar LightCompression On
</Directory>
-You should be all set usually after that.
+You should usually be all set after that.
-In more common cases you need to replace the line
+In more common cases, you will need to replace the line:
PerlHandler Apache::Registry
-in your initial configuration file with the set of the following lines:
+in your initial configuration file with the following lines:
PerlHandler Apache::RegistryFilter Apache::Dynagzip
PerlSetVar Filter On
PerlFixupHandler Apache::CompressClientFixup
-You might want to add optionally
+Optionally, you might add:
PerlSetVar LightCompression On
-to reduce the size of the stream even for clients incapable to speak gzip
-(like I<Microsoft Internet Explorer> over HTTP/1.0).
+to reduce the size of the stream for clients unable to speak gzip (like I<Microsoft Internet Explorer> over HTTP/1.0).
Finally, make sure you have somewhere declared
@@ -281,16 +261,30 @@
PerlModule Apache::Dynagzip
PerlModule Apache::CompressClientFixup
-This basic configuration uses many defaults.
-See C<Apache::Dynagzip> POD for further thin tuning if required.
+This basic configuration uses many defaults. See C<Apache::Dynagzip> POD for further fine tuning if required.
+
+Note, however, that C<Apache::RegistryFilter> is not I<yet another> C<Apache::Registry>.
+You may need to adjust your script in accordance with requirements of C<Apache::Filer> first,
+especially when the script generates any CGI/1.1-specific HTTP headers.
+You can test your compatibility with the C<Apache::Filter> chain using a temporary configuration like:
+
+ PerlModule Apache::Filter
+ <Directory /path/to/subdirectory>
+ SetHandler perl-script
+ PerlHandler Apache::RegistryFilter
+ PerlSendHeader On
+ Options +ExecCGI
+ PerlSetVar Filter On
+ </Directory>
+
+with no C<Apache::Dynagzip> involved.
+See C<Apache::Filter> documentation if you have any problems.
-=head1 Q: Is it possible to compress the output from Mason-driven application
-with C<Apache::Dynagzip>?
+=head1 Q: Is it possible to compress output from a Mason-driven application with C<Apache::Dynagzip>?
-=head2 A: Yes. C<HTML::Mason::ApacheHandler> is compatible with
-C<Apache::Filter> chain.
+=head2 A: Yes. C<HTML::Mason::ApacheHandler> is compatible with the C<Apache::Filter> chain.
-If your application is initially configured like
+If your application is initially configured like:
PerlModule HTML::Mason::ApacheHandler
<Directory /path/to/subdirectory>
@@ -300,7 +294,7 @@
</FilesMatch>
</Directory>
-you might want just to replace it with the following:
+you may wish to replace it with the following:
PerlModule HTML::Mason::ApacheHandler
PerlModule Apache::Dynagzip
@@ -317,57 +311,72 @@
You should be all set safely after that.
-In more common cases you need to replace the line
+In more common cases, you will need to replace the line:
PerlHandler HTML::Mason::ApacheHandler
-in your initial configuration file with the set of the following lines:
+in your initial configuration file with the following lines:
PerlHandler HTML::Mason::ApacheHandler Apache::Dynagzip
PerlSetVar Filter On
PerlFixupHandler Apache::CompressClientFixup
-You might want to add optionally
+Optionally, you might add:
PerlSetVar LightCompression On
-to reduce the size of the stream even for clients incapable to speak gzip
-(like I<Microsoft Internet Explorer> over HTTP/1.0).
+to reduce the size of the stream for clients unable to speak gzip (like I<Microsoft Internet Explorer> over HTTP/1.0).
Finally, make sure you have somewhere declared
PerlModule Apache::Dynagzip
PerlModule Apache::CompressClientFixup
-This basic configuration uses many defaults.
-See C<Apache::Dynagzip> POD for further thin tuning.
+This basic configuration uses many defaults. See C<Apache::Dynagzip> POD for further fine tuning.
-=head1 Q: Why is it important to keep control over chunk size?
+=head1 Q: Is commercial support available for C<Apache::Dynagzip>?
-=head2 A: It helps to reduce the latency of the response.
+=head2 A: Yes. I<Slav Company, Ltd.> provides commercial support for C<Apache::Dynagzip> worldwide.
-C<Apache::Dynagzip> is the only handler to date
-that begins transmission of compressed data as soon
-as the initial uncompressed pieces of data arrive
-from their source, at a time when the source process
-may not even have completed generating the full document
-it is sending.
-Transmission can therefore be taking place concurrent
-with creation of later document content.
-
-This feature is mainly beneficial for HTTP/1.1 requests,
-because HTTP/1.0 does not support chunks.
-
-I would also mention
-that the internal buffer in C<Apache::Dynagzip>
-always prevents Apache from the creating too short chunks over HTTP/1.1,
-or from transmitting too short pieces of data over HTTP/1.0.
-
-=head1 Q: Are there any content compression solutions for vanilla Apache 1.3.X?
-
-=head2 A: Yes, There are two compression modules
-written in C that are available
-for vanilla Apache 1.3.X:
+Since the author of C<Apache::Dynagzip> is employed by Slav Company, service is effective and consistent.
+
+=head1 Q: Why is it important to maintain a control over the chunk size?
+
+=head2 A: It helps to reduce response latency.
+
+C<Apache::Dynagzip> is the only handler to date that begins transmission of compressed data as soon
+as the initial uncompressed pieces of data arrive from their source, at a time when the source process
+may not even have completed generating the full document it is sending.
+Transmission can therefore take place concurrently with creation of later document content.
+
+This feature is mainly beneficial for HTTP/1.1 requests, because HTTP/1.0 does not support chunks.
+
+I would also mention that the internal buffer in C<Apache::Dynagzip> always prevents Apache
+from the creating too short chunks over HTTP/1.1, or from transmitting too short pieces of data over HTTP/1.0.
+
+=head1 Q: Is it worthwhile to strip leading blank spaces prior to gzip compression?
+
+=head2 A: Yes. It is usually worthwhile to do this.
+
+The benefits of blank space stripping are mostly significant for non-gzipped data transmissions.
+One can expect some 5-20% reduction in stream size on regular 'structured' HTML, JavaScript, CSS, XML, etc.,
+in this case at negligible cost in terms of CPU overhead and response delay.
+
+After applying gzip compression, the benefits of previously applied blank space stripping are usually reduced
+to some 0.5-1.0% of the resulting size, because gzip compresses blank spaces very effectively.
+It is still worthwhile, however, to perform blank space stripping because:
+
+=over 4
+
+=item * chances are that your handler will ultimately have to send an uncompressed response back to a known buggy client;
+
+=item * it really costs next-to-nothing, and every little bit helps to reduce the cost of data transmission, especially considering the cumulative effect of frequent repetitions.
+
+=back
+
+=head1 Q: Are there any content compression solutions for vanilla Apache 1.3?
+
+=head2 A: Yes. There are two compression modules written in C that are available for vanilla Apache 1.3:
=over 4
@@ -377,101 +386,94 @@
=item * mod_gzip
-an Apache handler written in C. Original author: Kevin Kiley, I<Remote
-Communications, Inc.> (U.S.)
+an Apache handler written in C, originally by Kevin Kiley, I<Remote Communications, Inc.> (U.S.)
=back
-Both of these modules support HTTP/1.0 only.
+See their respective documentation for further details.
=head1 Q: Can I compress the output of my site at the application level?
-=head2 A: Yes, if your web server is CGI/1.1 compatible and allows you
-to create specific HTTP headers from your application,
-or when you use an application framework
-that carries its own handler capable of compressing outbound data.
-
-For example, vanilla Apache 1.3.X is CGI/1.1 compatible.
-It allows development of CGI scripts/programs that might be generating
-compressed outgoing streams accomplished with specific HTTP headers.
-
-Alternatively, on mod_perl enabled Apache some application environments
-carry their own compression code that could be activated through
-the appropriate configurations:
+=head2 A: Yes, if your Web server is CGI/1.1 compatible and allows you to create specific HTTP headers from your application, or when you use an application framework that carries its own handler capable of compressing outbound data.
+
+For example, vanilla Apache 1.3 is CGI/1.1 compatible.
+It allows development of CGI scripts/programs that can generate compressed outgoing streams
+accomplished with specific HTTP headers.
+
+Alternatively, on mod_perl enabled Apache, some application environments carry their own compression code
+that can be activated through appropriate configuration:
C<Apache::ASP> does this with the C<CompressGzip> setting;
C<Apache::AxKit> uses the C<AxGzipOutput> setting to do this.
-See particular package documentation for details.
+See the documentation for the particular packages for details.
=head1 Q: Are there any content compression solutions for Apache-2?
-=head2 A: Yes, a core compression module written in C,
-C<mod_deflate>, has recently become available for Apache-2.
-
-C<mod_deflate> for Apache-2 is written by Ian Holsman (USA).
+=head2 A: Yes. A core compression module written in C, C<mod_deflate>, is available for Apache-2.
-This module supports HTTP/1.1 and is filters compatible.
+C<mod_deflate> for Apache-2 was written by Ian Holsman (USA).
-Despite its name C<mod_deflate> for Apache-2 provides C<gzip>-encoded content.
-It contains a set of configuration options sufficient to keep control
-over all recently known buggy web clients.
-
-=head1 Q: When C<Apache::Dynagzip> is supposed to be ported to Apache-2?
-
-=head2 A: There no recent plans to port C<Apache::Dynagzip> to Apache-2:
-
-C<mod_deflate> for Apache-2 seems to be capable to provide all basic functionality
-required for dynamic content compression:
+Despite its name, C<mod_deflate> for Apache-2 provides C<gzip>-encoded content.
+In accordance with the concept of output filters that was introduced in Apache-2,
+C<mod_deflate> is capable of gzipping outbound traffic from any content generator, including CGI, Java, mod_perl, etc.
=over 4
-=item * This module supports flushing over HTTP/1.1
+=item * This module supports flushing.
-=item * It is filters compatible.
+=item * It is output filter-compatible.
-=item * It has a set of configuration options to keep control over the buggy clients.
+=item * It has its own set of configuration options to maintain control over buggy clients.
=back
-The rest of the main C<Apache::Dynagzip> options could be easily addressed
-through the implementation of pretty tiny and specific accomplishing filters.
+=head1 Q: When is C<Apache::Dynagzip> supposed to be ported to Apache-2?
-=head1 Q: Where can I read the original descriptions of C<gzip>
-and C<deflate> formats?
+=head2 A: There are no current plans to port C<Apache::Dynagzip> to Apache-2:
-=head2 A: C<gzip> format is published as rfc1952,
-and C<deflate> format is published as rfc1951.
+C<mod_deflate> for Apache-2 is capable of providing all basic functionality required for effective
+dynamic content compression.
+The rest can be easily addressed through implementation of the accompanying specific, tiny filters.
+For instance, C<Apache::Clean>, which is already ported to Apache-2, can be used
+to strip unnecessary blank spaces from outbound streams.
+
+=head1 Q: Where can I read the original descriptions of the C<gzip> and C<deflate> formats?
+
+=head2 A: C<gzip> format is published as rfc1952, and C<deflate> format is published as rfc1951.
You can find many mirrors of RFC archives on the Internet.
Try, for instance, my favorite at L<http://www.ietf.org/rfc.html>
=head1 Q: Are there any known compression problems with specific browsers?
-=head2 A: Yes, Netscape 4 has problems with compressed cascading style sheets
-and JavaScript files.
+=head2 A: Yes. Netscape 4 has problems with compressed cascading style sheets and JavaScript files.
+
+You can use C<Apache::CompressClientFixup> to disable compression for these files dynamically on Apache-1.3.
+C<Apache::Dynagzip> is capable of providing so-called C<light compression> for these files.
-You can use C<Apache::CompressClientFixup> to disable compression
-for these files dynamically.
-C<Apache::Dynagzip> is capable of providing
-so-called C<light compression> for these files.
+On Apache-2, C<mod_deflate> can be configured to disable compression for these files dynamically,
+and the C<Apache::Clean> filter can be used to strip unnecessary blank spaces.
=head1 Q: Where can I find more information about the compression features of modern browsers?
=head2 A: Michael Schroepl maintains a highly valuable site
-Try it at L<http://www.schroepl.net/projekte/mod_gzip/browser.htm>
+See it at L<http://www.schroepl.net/projekte/mod_gzip/browser.htm>
=head1 Acknowledgments
-I highly appreciate efforts of Dan Hansen
-done in order to make this text better English...
+During this work, I received a great deal of real help
+from Kevin Kiley, Igor Sysoev, Michel Schroepl, and Henrik Nordstrom.
+I'm thankful to all subscribers of mod_perl users mailing list, mod_gzip mailing list, and squid users mailing list
+for the questions and discussions regarding the content compression.
+I'm especially thankful to Stas Bekman for the initiative to publish this FAQ on mod_perl Web site.
+I highly value patient efforts of Dan Hansen in making this text better English...
=head1 Maintainers
-The maintainer is the person you should contact with updates,
-corrections and patches.
+The maintainer is the person you should contact with updates, corrections and patches.
=over
@@ -491,7 +493,6 @@
=back
-Only the major authors are listed above. For contributors see the
-Changes file.
+Only the major authors are listed above. For contributors see the Changes file.
=cut
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