SWISH-FAQ(1) SWISH-E Documentation SWISH-FAQ(1)NAME
The Swish-e FAQ - Answers to Common Questions
OVERVIEW
List of commonly asked and answered questions. Please review this doc‐
ument before asking questions on the Swish-e discussion list.
General Questions
What is Swish-e?
Swish-e is Simple Web Indexing System for Humans - Enhanced. With it,
you can quickly and easily index directories of files or remote web
sites and search the generated indexes for words and phrases.
So, is Swish-e a search engine?
Well, yes. Probably the most common use of Swish-e is to provide a
search engine for web sites. The Swish-e distribution includes CGI
scripts that can be used with it to add a search engine for your web
site. The CGI scripts can be found in the example directory of the
distribution package. See the README file for information about the
scripts.
But Swish-e can also be used to index all sorts of data, such as email
messages, data stored in a relational database management system, XML
documents, or documents such as Word and PDF documents -- or any combi‐
nation of those sources at the same time. Searches can be limited to
fields or MetaNames within a document, or limited to areas within an
HTML document (e.g. body, title). Programs other than CGI applications
can use Swish-e, as well.
Should I upgrade if I'm already running a previous version of Swish-e?
A large number of bug fixes, feature additions, and logic corrections
were made in version 2.2. In addition, indexing speed has been drasti‐
cally improved (reports of indexing times changing from four hours to 5
minutes), and major parts of the indexing and search parsers have been
rewritten. There's better debugging options, enhanced output formats,
more document meta data (e.g. last modified date, document summary),
options for indexing from external data sources, and faster spidering
just to name a few changes. (See the CHANGES file for more informa‐
tion.
Since so much effort has gone into version 2.2, support for previous
versions will probably be limited.
Are there binary distributions available for Swish-e on platform foo?
Foo? Well, yes there are some binary distributions available. Please
see the Swish-e web site for a list at http://swish-e.org/.
In general, it is recommended that you build Swish-e from source, if
possible.
Do I need to reindex my site each time I upgrade to a new Swish-e ver‐
sion?
At times it might not strictly be necessary, but since you don't really
know if anything in the index has changed, it is a good rule to rein‐
dex.
What's the advantage of using the libxml2 library for parsing HTML?
Swish-e may be linked with libxml2, a library for working with HTML and
XML documents. Swish-e can use libxml2 for parsing HTML and XML docu‐
ments.
The libxml2 parser is a better parser than Swish-e's built-in HTML
parser. It offers more features, and it does a much better job at
extracting out the text from a web page. In addition, you can use the
"ParserWarningLevel" configuration setting to find structural errors in
your documents that could (and would with Swish-e's HTML parser) cause
documents to be indexed incorrectly.
Libxml2 is not required, but is strongly recommended for parsing HTML
documents. It's also recommended for parsing XML, as it offers many
more features than the internal Expat xml.c parser.
The internal HTML parser will have limited support, and does have a
number of bugs. For example, HTML entities may not always be correctly
converted and properties do not have entities converted. The internal
parser tends to get confused when invalid HTML is parsed where the
libxml2 parser doesn't get confused as often. The structure is better
detected with the libxml2 parser.
If you are using the Perl module (the C interface to the Swish-e
library) you may wish to build two versions of Swish-e, one with the
libxml2 library linked in the binary, and one without, and build the
Perl module against the library without the libxml2 code. This is to
save space in the library. Hopefully, the library will someday soon be
split into indexing and searching code (volunteers welcome).
Does Swish-e include a CGI interface?
Yes. Kind of.
There's two example CGI scripts included, swish.cgi and search.cgi.
Both are installed at $prefix/lib/swish-e.
Both require a bit of work to setup and use. Swish.cgi is probably
what most people will want to use as it contains more features.
Search.cgi is for those that want to start with a small script and cus‐
tomize it to fit their needs.
An example of using swish.cgi is given in the INSTALL man page, and it
the swish.cgi documentation. Like often is the case, it will be easier
to use if you first read the documentation.
Please use caution about CGI scripts found on the Internet for use with
Swish-e. Some are not secure.
The included example CGI scripts were designed with security in mind.
Regardless, you are encouraged to have your local Perl expert review it
(and all other CGI scripts you use) before placing it into production.
This is just a good policy to follow.
How secure is Swish-e?
We know of no security issues with using Swish-e. Careful attention
has been made with regard to common security problems such as buffer
overruns when programming Swish-e.
The most likely security issue with Swish-e is when it is run via a
poorly written CGI interface. This is not limited to CGI scripts writ‐
ten in Perl, as it's just as easy to write an insecure CGI script in C,
Java, PHP, or Python. A good source of information is included with
the Perl distribution. Type "perldoc perlsec" at your local prompt for
more information. Another must-read document is located at
"http://www.w3.org/Security/faq/wwwsf4.html".
Note that there are many free yet insecure and poorly written CGI
scripts available -- even some designed for use with Swish-e. Please
carefully review any CGI script you use. Free is not such a good price
when you get your server hacked...
Should I run Swish-e as the superuser (root)?
No. Never.
What files does Swish-e write?
Swish writes the index file, of course. This is specified with the
"IndexFile" configuration directive or by the "-f" command line switch.
The index file is actually a collection of files, but all start with
the file name specified with the "IndexFile" directive or the "-f" com‐
mand line switch.
For example, the file ending in .prop contains the document properties.
When creating the index files Swish-e appends the extension .temp to
the index file names. When indexing is complete Swish-e renames the
.temp files to the index files specified by "IndexFile" or "-f". This
is done so that existing indexes remain untouched until it completes
indexing.
Swish-e also writes temporary files in some cases during indexing (e.g.
"-s http", "-s prog" with filters), when merging, and when using "-e").
Temporary files are created with the mkstemp(3) function (with 0600
permission on unix-like operating systems).
The temporary files are created in the directory specified by the envi‐
ronment variables "TMPDIR" and "TMP" in that order. If those are not
set then swish uses the setting the configuration setting TmpDir. Oth‐
erwise, the temporary file will be located in the current directory.
Can I index PDF and MS-Word documents?
Yes, you can use a Filter to convert documents while indexing, or you
can use a program that "feeds" documents to Swish-e that have already
been converted. See "Indexing" below.
Can I index documents on a web server?
Yes, Swish-e provides two ways to index (spider) documents on a web
server. See "Spidering" below.
Swish-e can retrieve documents from a file system or from a remote web
server. It can also execute a program that returns documents back to
it. This program can retrieve documents from a database, filter com‐
pressed documents files, convert PDF files, extract data from mail ar‐
chives, or spider remote web sites.
Can I implement keywords in my documents?
Yes, Swish-e can associate words with MetaNames while indexing, and you
can limit your searches to these MetaNames while searching.
In your HTML files you can put keywords in HTML META tags or in XML
blocks.
META tags can have two formats in your source documents:
<META NAME="DC.subject" CONTENT="digital libraries">
And in XML format (can also be used in HTML documents when using
libxml2):
<meta2>
Some Content
</meta2>
Then, to inform Swish-e about the existence of the meta name in your
documents, edit the line in your configuration file:
MetaNames DC.subject meta1 meta2
When searching you can now limit some or all search terms to that
MetaName. For example, to look for documents that contain the word
apple and also have either fruit or cooking in the DC.subject meta tag.
What are document properties?
A document property is typically data that describes the document. For
example, properties might include a document's path name, its last mod‐
ified date, its title, or its size. Swish-e stores a document's prop‐
erties in the index file, and they can be reported back in search
results.
Swish-e also uses properties for sorting. You may sort your results by
one or more properties, in ascending or descending order.
Properties can also be defined within your documents. HTML and XML
files can specify tags (see previous question) as properties. The con‐
tents of these tags can then be returned with search results. These
user-defined properties can also be used for sorting search results.
For example, if you had the following in your documents
<meta name="creator" content="accounting department">
and "creator" is defined as a property (see "PropertyNames" in SWISH-
CONFIG) Swish-e can return "accounting department" with the result for
that document.
swish-e -w foo -p creator
Or for sorting:
swish-e -w foo -s creator
What's the difference between MetaNames and PropertyNames?
MetaNames allows keywords searches in your documents. That is, you can
use MetaNames to restrict searches to just parts of your documents.
PropertyNames, on the other hand, define text that can be returned with
results, and can be used for sorting.
Both use meta tags found in your documents (as shown in the above two
questions) to define the text you wish to use as a property or meta
name.
You may define a tag as both a property and a meta name. For example:
<meta name="creator" content="accounting department">
placed in your documents and then using configuration settings of:
PropertyNames creator
MetaNames creator
will allow you to limit your searches to documents created by account‐
ing:
swish-e -w 'foo and creator=(accounting)'
That will find all documents with the word "foo" that also have a cre‐
ator meta tag that contains the word "accounting". This is using
MetaNames.
And you can also say:
swish-e -w foo -p creator
which will return all documents with the word "foo", but the results
will also include the contents of the "creator" meta tag along with
results. This is using properties.
You can use properties and meta names at the same time, too:
swish-e -w creator=(accounting or marketing) -p creator -s creator
That searches only in the "creator" meta name for either of the words
"accounting" or "marketing", prints out the contents of the contents of
the "creator" property, and sorts the results by the "creator" property
name.
(See also the "-x" output format switch in SWISH-RUN.)
Can Swish-e index multi-byte characters?
No. This will require much work to change. But, Swish-e works with
eight-bit characters, so many characters sets can be used. Note that
it does call the ANSI-C tolower() function which does depend on the
current locale setting. See locale(7) for more information.
Indexing
How do I pass Swish-e a list of files to index?
Currently, there is not a configuration directive to include a file
that contains a list of files to index. But, there is a directive to
include another configuration file.
IncludeConfigFile /path/to/other/config
And in "/path/to/other/config" you can say:
IndexDir file1 file2 file3 file4 file5 ...
IndexDir file20 file21 file22
You may also specify more than one configuration file on the command
line:
./swish-e -c config_one config_two config_three
Another option is to create a directory with symbolic links of the
files to index, and index just that directory.
How does Swish-e know which parser to use?
Swish can parse HTML, XML, and text documents. The parser is set by
associating a file extension with a parser by the "IndexContents"
directive. You may set the default parser with the "DefaultContents"
directive. If a document is not assigned a parser it will default to
the HTML parser (HTML2 if built with libxml2).
You may use Filters or an external program to convert documents to
HTML, XML, or text.
Can I reindex and search at the same time?
Yes. Starting with version 2.2 Swish-e indexes to temporary files, and
then renames the files when indexing is complete. On most systems
renames are atomic. But, since Swish-e also generates more than one
file during indexing there will be a very short period of time between
renaming the various files when the index is out of sync.
Settings in src/config.h control some options related to temporary
files, and their use during indexing.
Can I index phrases?
Phrases are indexed automatically. To search for a phrase simply place
double quotes around the phrase.
For example:
swish-e -w 'free and "fast search engine"'
How can I prevent phrases from matching across sentences?
Use the BumpPositionCounterCharacters configuration directive.
Swish-e isn't indexing a certain word or phrase.
There are a number of configuration parameters that control what Swish-
e considers a "word" and it has a debugging feature to help pinpoint
any indexing problems.
Configuration file directives (SWISH-CONFIG) "WordCharacters", "Begin‐
Characters", "EndCharacters", "IgnoreFirstChar", and "IgnoreLastChar"
are the main settings that Swish-e uses to define a "word". See SWISH-
CONFIG and SWISH-RUN for details.
Swish-e also uses compile-time defaults for many settings. These are
located in src/config.h file.
Use of the command line arguments "-k", "-v" and "-T" are useful when
debugging these problems. Using "-T INDEXED_WORDS" while indexing will
display each word as it is indexed. You should specify one file when
using this feature since it can generate a lot of output.
./swish-e -c my.conf -i problem.file -T INDEXED_WORDS
You may also wish to index a single file that contains words that are
or are not indexing as you expect and use -T to output debugging infor‐
mation about the index. A useful command might be:
./swish-e -f index.swish-e -T INDEX_FULL
Once you see how Swish-e is parsing and indexing your words, you can
adjust the configuration settings mentioned above to control what words
are indexed.
Another useful command might be:
./swish-e -c my.conf -i problem.file -T PARSED_WORDS INDEXED_WORDS
This will show white-spaced words parsed from the document
(PARSED_WORDS), and how those words are split up into separate words
for indexing (INDEXED_WORDS).
How do I keep Swish-e from indexing numbers?
Swish-e indexes words as defined by the "WordCharacters" setting, as
described above. So to avoid indexing numbers you simply remove digits
from the "WordCharacters" setting.
There are also some settings in src/config.h that control what "words"
are indexed. You can configure swish to never index words that are all
digits, vowels, or consonants, or that contain more than some consecu‐
tive number of digits, vowels, or consonants. In general, you won't
need to change these settings.
Also, there's an experimental feature called "IgnoreNumberChars" which
allows you to define a set of characters that describe a number. If a
word is made up of only those characters it will not be indexed.
Swish-e crashes and burns on a certain file. What can I do?
This shouldn't happen. If it does please post to the Swish-e discus‐
sion list the details so it can be reproduced by the developers.
In the mean time, you can use a "FileRules" directive to exclude the
particular file name, or pathname, or its title. If there are serious
problems in indexing certain types of files, they may not have valid
text in them (they may be binary files, for instance). You can use
NoContents to exclude that type of file.
Swish-e will issue a warning if an embedded null character is found in
a document. This warning will be an indication that you are trying to
index binary data. If you need to index binary files try to find a
program that will extract out the text (e.g. strings(1), catdoc(1),
pdftotext(1)).
How to I prevent indexing of some documents?
When using the file system to index your files you can use the
"FileRules" directive. Other than "FileRules title", "FileRules" only
works with the file system ("-S fs") indexing method, not with "-S
prog" or "-S http".
If you are spidering a site you have control over, use a robots.txt
file in your document root. This is a standard way to excluded files
from search engines, and is fully supported by Swish-e. See
http://www.robotstxt.org/
If spidering a website with the included spider.pl program then add any
necessary tests to the spider's configuration file. Type <perldoc spi‐
der.pl> in the "prog-bin" directory for details or see the spider docu‐
mentation on the Swish-e website. Look for the section on callback
functions.
If using the libxml2 library for parsing HTML (which you probably are),
you may also use the Meta Robots Exclusion in your documents:
<meta name="robots" content="noindex">
See the obeyRobotsNoIndex directive.
How do I prevent indexing parts of a document?
To prevent Swish-e from indexing a common header, footer, or navigation
bar, AND you are using libxml2 for parsing HTML, then you may use a
fake HTML tag around the text you wish to ignore and use the
"IgnoreMetaTags" directive. This will generate an error message if the
"ParserWarningLevel" is set as it's invalid HTML.
"IgnoreMetaTags" works with XML documents (and HTML documents when
using libxml2 as the parser), but not with documents parsed by the text
(TXT) parser.
If you are using the libxml2 parser (HTML2 and XML2) then you can use
the the following comments in your documents to prevent indexing:
<!-- SwishCommand noindex -->
<!-- SwishCommand index -->
and/or these may be used also:
<!-- noindex -->
<!-- index -->
How do I modify the path or URL of the indexed documents.
Use the "ReplaceRules" configuration directive to rewrite path names
and URLs. If you are using "-S prog" input method you may set the path
to any string.
How can I index data from a database?
Use the "prog" document source method of indexing. Write a program to
extract out the data from your database, and format it as XML, HTML, or
text. See the examples in the "prog-bin" directory, and the next ques‐
tion.
How do I index my PDF, Word, and compressed documents?
Swish-e can internally only parse HTML, XML and TXT (text) files by
default, but can make use of filters that will convert other types of
files such as MS Word documents, PDF, or gzipped files into one of the
file types that Swish-e understands.
Please see SWISH-CONFIG and the examples in the filters and filter-bin
directory for more information.
See the next question to learn about the filtering options with
Swish-e.
How do I filter documents?
The term "filter" in Swish-e means the converstion of a document of one
type (one that swish-e cannot index directly) into a type that Swish-e
can index, namely HTML, plain text, or XML. To add to the confusion,
there are a number of ways to accomplish this in Swish-e. So here's a
bit of background.
The FileFilter directive was added to swish first. This feature allows
you to specify a program to run for documents that match a given file
extension. For example, to filter PDF files (files that end in .pdf)
you can specify the configuation setting of:
FileFilter .pdf pdftotext "'%p' -"
which says to run the program "pdftotext" passing it the pathname of
the file (%p) and a dash (which tells pdftotext to output to stdout).
Then for each .pdf file Swish-e runs this program and reads in the fil‐
tered document from the output from the filter program.
This has the advantage that it is easy to setup -- a single line in the
config file is all that is needed to add the filter into Swish-e. But
it also has a number of problems. For example, if you use a Perl
script to do your filtering it can be very slow since the filter script
must be run (and thus compiled) for each processed document. This is
exacerbated when using the -S http method since the -S http method also
uses a Perl script that is run for every URL fetched. Also, when using
-S prog method of input (reading input from a program) using FileFilter
means that Swish-e must first read the file in from the external pro‐
gram and then write the file out to a temporary file before running the
filter.
With -S prog it makes much more sense to filter the document in the
program that is fetching the documents than to have swish-e read the
file into memory, write it to a temporary file and then run an external
program.
The Swish-e distribution contains a couple of example -S prog programs.
spider.pl is a reasonably full-featured web spider that offers many
more options than the -S http method. And it is much faster than run‐
ning -S http, too.
The spider has a perl configuration file, which means you can add pro‐
gramming logic right into the configuration file without editing the
spider program. One bit of logic that is provided in the spider's con‐
figuration file is a "call-back" function that allows you to filter the
content. In other words, before the spider passes a fetched web docu‐
ment to swish for indexing the spider can call a simple subroutine in
the spider's configuration file passing the document and its content
type. The subroutine can then look at the content type and decide if
the document needs to be filtered.
For example, when processing a document of type "application/msword"
the call-back subroutine might call the doc2txt.pm perl module, and a
document of type "appliation/pdf" could use the pdf2html.pm module.
The prog-bin/SwishSpiderConfig.pl file shows this usage.
This system works reasonably well, but also means that more work is
required to setup the filters. First, you must explicitly check for
specific content types and then call the appropriate Perl module, and
second, you have to know how each module must be called and how each
returns the possibly modified content.
In comes SWISH::Filter.
To make things easier the SWISH::Filter Perl module was created. The
idea of this module is that there is one interface used to filter all
types of documents. So instead of checking for specific types of con‐
tent you just pass the content type and the document to the SWISH::Fil‐
ter module and it returns a new content type and document if it was
filtered. The filters that do the actual work are designed with a
standard interface and work like filter "plug-ins". Adding new filters
means just downloading the filter to a directory and no changes are
needed to the spider's configuation file. Download a filter for Post‐
script and next time you run indexing your Postscript files will be
indexed.
Since the filters are standardized, hopefully when you have the need to
filter documents of a specific type there will already be a filter
ready for your use.
Now, note that the perl modules may or may not do the actual conversion
of a document. For example, the PDF conversion module calls the
pdfinfo and pdftotext programs. Those programs (part of the Xpfd pack‐
age) must be installed separately from the filters.
The SwishSpiderConfig.pl examle spider configuration file shows how to
use the SWISH::Filter module for filtering. This file is installed at
$prefix/share/doc/swish-e/examples/prog-bin, where $prefix is normally
/usr/local on unix-type machines.
The SWISH::Filter method of filtering can also be used with the -S http
method of indexing. By default the swishspider program (the Perl
helper script that fetches documents from the web) will attempt to use
the SWISH::Filter module if it can be found in Perls library path.
This path is set automatically for spider.pl but not for swishspider
(because it would slow down a method that's already slow and spider.pl
is recommended over the -S http method).
Therefore, all that's required to use this system with -S http is set‐
ting the @INC array to point to the filter directory.
For example, if the swish-e distribution was unpacked into ~/swish-e:
PERL5LIB=~/swish-e/filters swish-e -c conf -S http
will allow the -S http method to make use of the SWISH::Filter module.
Note that if you are not using the SWISH::Filter module you may wish to
edit the swishspider program and disable the use of the SWISH::Filter
module using this setting:
use constant USE_FILTERS => 0; # disable SWISH::Filter
This prevents the program from attempting to use the SWISH::Filter mod‐
ule for every non-text URL that is fetched. Of course, if you are con‐
cerned with indexing speed you should be using the -S prog method with
spider.pl instead of -S http.
If you are not spidering, but you still want to make use of the
SWISH::Filter module for filtering you can use the DirTree.pl program
(in $prefix/lib/swish-e). This is a simple program that traverses the
file system and uses SWISH::Filter for filtering.
Here's two examples of how to run a filter program, one using Swish-e's
"FileFilter" directive, another using a "prog" input method program.
See the SwishSpiderConfig.pl file for an example of using the
SWISH::Filter module.
These filters simply use the program "/bin/cat" as a filter and only
indexes .html files.
First, using the "FileFilter" method, here's the entire configuration
file (swish.conf):
IndexDir .
IndexOnly .html
FileFilter .html "/bin/cat" "'%p'"
and index with the command
swish-e -c swish.conf -v 1
Now, the same thing with using the "-S prog" document source input
method and a Perl program called catfilter.pl. You can see that's it's
much more work than using the "FileFilter" method above, but provides a
place to do additional processing. In this example, the "prog" method
is only slightly faster. But if you needed a perl script to run as a
FileFilter then "prog" will be significantly faster.
#!/usr/local/bin/perl -w
use strict;
use File::Find; # for recursing a directory tree
$/ = undef;
find(
{ wanted => \&wanted, no_chdir => 1, },
'.',
);
sub wanted {
return if -d;
return unless /\.html$/;
my $mtime = (stat)[9];
my $child = open( FH, '-⎪' );
die "Failed to fork $!" unless defined $child;
exec '/bin/cat', $_ unless $child;
my $content = <FH>;
my $size = length $content;
print <<EOF;
Content-Length: $size
Last-Mtime: $mtime
Path-Name: $_
EOF
print <FH>;
}
And index with the command:
swish-e -S prog -i ./catfilter.pl -v 1
This example will probably not work under Windows due to the '-⎪' open.
A simple piped open may work just as well:
That is, replace:
my $child = open( FH, '-⎪' );
die "Failed to fork $!" unless defined $child;
exec '/bin/cat', $_ unless $child;
with this:
open( FH, "/bin/cat $_ ⎪" ) or die $!;
Perl will try to avoid running the command through the shell if meta
characters are not passed to the open. See "perldoc -f open" for more
information.
Eh, but I just want to know how to index PDF documents!
See the examples in the conf directory and the comments in the Swish‐
SpiderConfig.pl file.
See the previous question for the details on filtering. The method you
decide to use will depend on how fast you want to index, and your com‐
fort level with using Perl modules.
Regardless of the filtering method you use you will need to install the
Xpdf packages available from http://www.foolabs.com/xpdf/.
I'm using Windows and can't get Filters or the prog input method to
work!
Both the "-S prog" input method and filters use the "popen()" system
call to run the external program. If your external program is, for
example, a perl script, you have to tell Swish-e to run perl, instead
of the script. Swish-e will convert forward slashes to backslashes
when running under Windows.
For example, you would need to specify the path to perl as (assuming
this is where perl is on your system):
IndexDir e:/perl/bin/perl.exe
Or run a filter like:
FileFilter .foo e:/perl/bin/perl.exe 'myscript.pl "%p"'
It's often easier to just install Linux.
How do I index non-English words?
Swish-e indexes 8-bit characters only. This is the ISO 8859-1 Latin-1
character set, and includes many non-English letters (and symbols). As
long as they are listed in "WordCharacters" they will be indexed.
Actually, you probably can index any 8-bit character set, as long as
you don't mix character sets in the same index and don't use libxml2
for parsing (see below).
The "TranslateCharacters" directive (SWISH-CONFIG) can translate char‐
acters while indexing and searching. You may specify the mapping of
one character to another character with the "TranslateCharacters"
directive.
"TranslateCharacters :ascii7:" is a predefined set of characters that
will translate eight-bit characters to ascii7 characters. Using the
":ascii7:" rule will, for example, translate "���" to "aac". This
means: searching "�elik", "�elik" or "celik" will all match the same
word.
Note: When using libxml2 for parsing, parsed documents are converted
internally (within libxml2) to UTF-8. This is converted to ISO 8859-1
Latin-1 when indexing. In cases where a string can not be converted
from UTF-8 to ISO 8859-1 (because it contains non 8859-1 characters),
the string will be sent to Swish-e in UTF-8 encoding. This will
results in some words indexed incorrectly. Setting "ParserWarn‐
ingLevel" to 1 or more will display warnings when UTF-8 to 8859-1 con‐
version fails.
Can I add/remove files from an index?
Try building swish-e with the "--enable-incremental" option.
The rest of this FAQ applies to the default swish-e format.
Swish-e currently has no way to add or remove items from its index.
But, Swish-e indexes so quickly that it's often possible to reindex the
entire document set when a file needs to be added, modified or removed.
If you are spidering a remote site then consider caching documents
locally compressed.
Incremental additions can be handled in a couple of ways, depending on
your situation. It's probably easiest to create one main index every
night (or every week), and then create an index of just the new files
between main indexing jobs and use the "-f" option to pass both indexes
to Swish-e while searching.
You can merge the indexes into one index (instead of using -f), but
it's not clear that this has any advantage over searching multiple
indexes.
How does one create the incremental index?
One method is by using the "-N" switch to pass a file path to Swish-e
when indexing. It will only index files that have a last modification
date "newer" than the file supplied with the "-N" switch.
This option has the disadvantage that Swish-e must process every file
in every directory as if they were going to be indexed (the test for
"-N" is done last right before indexing of the file contents begin and
after all other tests on the file have been completed) -- all that just
to find a few new files.
Also, if you use the Swish-e index file as the file passed to "-N"
there may be files that were added after indexing was started, but
before the index file was written. This could result in a file not
being added to the index.
Another option is to maintain a parallel directory tree that contains
symlinks pointing to the main files. When a new file is added (or
changed) to the main directory tree you create a symlink to the real
file in the parallel directory tree. Then just index the symlink
directory to generate the incremental index.
This option has the disadvantage that you need to have a central pro‐
gram that creates the new files that can also create the symlinks.
But, indexing is quite fast since Swish-e only has to look at the files
that need to be indexed. When you run full indexing you simply unlink
(delete) all the symlinks.
Both of these methods have issues where files could end up in both
indexes, or files being left out of an index. Use of file locks while
indexing, and hash lookups during searches can help prevent these prob‐
lems.
I run out of memory trying to index my files.
It's true that indexing can take up a lot of memory! Swish-e is
extremely fast at indexing, but that comes at the cost of memory.
The best answer is install more memory.
Another option is use the "-e" switch. This will require less memory,
but indexing will take longer as not all data will be stored in memory
while indexing. How much less memory and how much more time depends on
the documents you are indexing, and the hardware that you are using.
Here's an example of indexing all .html files in /usr/doc on Linux.
This first example is without "-e" and used about 84M of memory:
270279 unique words indexed.
23841 files indexed. 177640166 total bytes.
Elapsed time: 00:04:45 CPU time: 00:03:19
This is with "-e", and used about 26M or memory:
270279 unique words indexed.
23841 files indexed. 177640166 total bytes.
Elapsed time: 00:06:43 CPU time: 00:04:12
You can also build a number of smaller indexes and then merge together
with "-M". Using "-e" while merging will save memory.
Finally, if you do build a number of smaller indexes, you can specify
more than one index when searching by using the "-f" switch. Sorting
large results sets by a property will be slower when specifying multi‐
ple index files while searching.
"too many open files" when indexing with -e option
Some platforms report "too many open files" when using the -e economy
option. The -e feature uses many temporary files (something like 377)
plus the index files and this may exceed your system's limits.
Depending on your platform you may need to set "ulimit" or "unlimit".
For example, under Linux bash shell:
$ ulimit -n 1024
Or under an old Sparc
% unlimit openfiles
My system admin says Swish-e uses too much of the CPU!
That's a good thing! That expensive CPU is supposed to be busy.
Indexing takes a lot of work -- to make indexing fast much of the work
is done in memory which reduces the amount of time Swish-e is waiting
on I/O. But, there's two things you can try:
The "-e" option will run Swish-e in economy mode, which uses the disk
to store data while indexing. This makes Swish-e run somewhat slower,
but also uses less memory. Since it is writing to disk more often it
will be spending more time waiting on I/O and less time in CPU. Maybe.
The other thing is to simply lower the priority of the job using the
nice(1) command:
/bin/nice -15 swish-e -c search.conf
If concerned about searching time, make sure you are using the -b and
-m switches to only return a page at a time. If you know that your
result sets will be large, and that you wish to return results one page
at a time, and that often times many pages of the same query will be
requested, you may be smart to request all the documents on the first
request, and then cache the results to a temporary file. The perl mod‐
ule File::Cache makes this very simple to accomplish.
Spidering
How can I index documents on a web server?
If possible, use the file system method "-S fs" of indexing to index
documents in you web area of the file system. This avoids the overhead
of spidering a web server and is much faster. ("-S fs" is the default
method if "-S" is not specified).
If this is impossible (the web server is not local, or documents are
dynamically generated), Swish-e provides two methods of spidering.
First, it includes the http method of indexing "-S http". A number of
special configuration directives are available that control spidering
(see "Directives for the HTTP Access Method Only" in SWISH-CONFIG). A
perl helper script (swishspider) is included in the src directory to
assist with spidering web servers. There are example configurations for
spidering in the conf directory.
As of Swish-e 2.2, there's a general purpose "prog" document source
where a program can feed documents to it for indexing. A number of
example programs can be found in the "prog-bin" directory, including a
program to spider web servers. The provided spider.pl program is full-
featured and is easily customized.
The advantage of the "prog" document source feature over the "http"
method is that the program is only executed one time, where the swish‐
spider.pl program used in the "http" method is executed once for every
document read from the web server. The forking of Swish-e and compil‐
ing of the perl script can be quite expensive, time-wise.
The other advantage of the "spider.pl" program is that it's simple and
efficient to add filtering (such as for PDF or MS Word docs) right into
the spider.pl's configuration, and it includes features such as MD5
checks to prevent duplicate indexing, options to avoid spidering some
files, or index but avoid spidering. And since it's a perl program
there's no limit on the features you can add.
Why does swish report "./swishspider: not found"?
Does the file swishspider exist where the error message displays? If
not, either set the configuration option SpiderDirectory to point to
the directory where the swishspider program is found, or place the
swishspider program in the current directory when running swish-e.
If you are running Windows, make sure "perl" is in your path. Try typ‐
ing perl from a command prompt.
If you not running windows, make sure that the shebang line (the first
line of the swishspider program that starts with #!) points to the cor‐
rect location of perl. Typically this will be /usr/bin/perl or
/usr/local/bin/perl. Also, make sure that you have execute and read
permissions on swishspider.
The swishspider perl script is only used with the -S http method of
indexing.
I'm using the spider.pl program to spider my web site, but some large
files are not indexed.
The "spider.pl" program has a default limit of 5MB file size. This can
be changed with the "max_size" parameter setting. See "perldoc spi‐
der.pl" for more information.
I still don't think all my web pages are being indexed.
The spider.pl program has a number of debugging switches and can be
quite verbose in telling you what's happening, and why. See "perldoc
spider.pl" for instructions.
Swish is not spidering Javascript links!
Swish cannot follow links generated by Javascript, as they are gener‐
ated by the browser and are not part of the document.
How do I spider other websites and combine it with my own (filesystem)
index?
You can either merge "-M" two indexes into a single index, or use "-f"
to specify more than one index while searching.
You will have better results with the "-f" method.
Searching
How do I limit searches to just parts of the index?
If you can identify "parts" of your index by the path name you have two
options.
The first options is by indexing the document path. Add this to your
configuration:
MetaNames swishdocpath
Now you can search for words or phrases in the path name:
swish-e -w 'foo AND swishdocpath=(sales)'
So that will only find documents with the word "foo" and where the
file's path contains "sales". That might not works as well as you
like, though, as both of these paths will match:
/web/sales/products/index.html
/web/accounting/private/sales_we_messed_up.html
This can be solved by searching with a phrase (assuming "/" is not a
WordCharacter):
swish-e -w 'foo AND swishdocpath=("/web/sales/")'
swish-e -w 'foo AND swishdocpath=("web sales")' (same thing)
The second option is a bit more powerful. With the "ExtractPath"
directive you can use a regular expression to extract out a sub-set of
the path and save it as a separate meta name:
MetaNames department
ExtractPath department regex !^/web/([^/]+).+$!$1/
Which says match a path that starts with "/web/" and extract out every‐
thing after that up to, but not including the next "/" and save it in
variable $1, and then match everything from the "/" onward. Then
replace the entire matches string with $1. And that gets indexed as
meta name "department".
Now you can search like:
swish-e -w 'foo AND department=sales'
and be sure that you will only match the documents in the /www/sales/*
path. Note that you can map completely different areas of your file
system to the same metaname:
# flag the marketing specific pages
ExtractPath department regex !^/web/(marketing⎪sales)/.+$!marketing/
ExtractPath department regex !^/internal/marketing/.+$!marketing/
# flag the technical departments pages
ExtractPath department regex !^/web/(tech⎪bugs)/.+$!tech/
Finally, if you have something more complicated, use "-S prog" and
write a perl program or use a filter to set a meta tag when processing
each file.
How is ranking calculated?
The "swishrank" property value is calculated based on which Ranking
Scheme (or algorithm) you have selected. In this discussion, any time
the word fancy is used, you should consult the actual code for more
details. It is open source, after all.
Things you can do to affect ranking:
MetaNamesRank
You may configure your index to bias certain metaname values more
or less than others. See the "MetaNamesRank" configuration option
in SWISH-CONFIG.
IgnoreTotalWordCountWhenRanking
Set to 1 (default) or 0 in your config file. See SWISH-CONFIG.
NOTE: You must set this to 0 to use the IDF Ranking Scheme.
structure
Each term's position in each HTML document is given a structure
value based on the context in which the word appears. The structure
value is used to artificially inflate the frequency of each term in
that particular document. These structural values are defined in
config.h:
#define RANK_TITLE 7
#define RANK_HEADER 5
#define RANK_META 3
#define RANK_COMMENTS 1
#define RANK_EMPHASIZED 0
For example, if the word "foo" appears in the title of a document,
the Scheme will treat that document as if "foo" appeared 7 addi‐
tional times.
All Schemes share the following characteristics:
AND searches
The rank value is averaged for all AND'd terms. Terms within a set
of parentheses () are averaged as a single term (this is an
acknowledged weakness and is on the TODO list).
OR searches
The rank value is summed and then doubled for each pair of OR'd
terms. This results in higher ranks for documents that have multi‐
ple OR'd terms.
scaled rank
After a document's raw rank score is calculated, a final rank score
is calculated using a fancy "log()" function. All the documents are
then scaled against a base score of 1000. The top-ranked document
will therefore always have a "swishrank" value of 1000.
Here is a brief overview of how the different Schemes work. The number
in parentheses after the name is the value to invoke that scheme with
"swish-e -R" or "RankScheme()".
Default (0)
The default ranking scheme considers the number of times a term
appears in a document (frequency), the MetaNamesRank and the struc‐
ture value. The rank might be summarized as:
DocRank = Sum of ( structure + metabias )
Consider this output with the DEBUG_RANK variable set at compile
time:
Ranking Scheme: 0
Word entry 0 at position 6 has struct 7
Word entry 1 at position 64 has struct 41
Word entry 2 at position 71 has struct 9
Word entry 3 at position 132 has struct 9
Word entry 4 at position 154 has struct 9
Word entry 5 at position 423 has struct 73
Word entry 6 at position 541 has struct 73
Word entry 7 at position 662 has struct 73
File num: 1104. Raw Rank: 21. Frequency: 8 scaled rank: 30445
Structure tally:
struct 0x7 = count of 1 ( HEAD TITLE FILE ) x rank map of 8 = 8
struct 0x9 = count of 3 ( BODY FILE ) x rank map of 1 = 3
struct 0x29 = count of 1 ( HEADING BODY FILE ) x rank map of 6 = 6
struct 0x49 = count of 3 ( EM BODY FILE ) x rank map of 1 = 3
Every word instance starts with a base score of 1. Then for each
instance of your word, a running sum is taken of the structural
value of that word position plus any bias you've configured. In
the example above, the raw rank is "1 + 8 + 3 + 6 + 3 = 21".
Consider this line:
struct 0x7 = count of 1 ( HEAD TITLE FILE ) x rank map of 8 = 8
That means there was one instance of our word in the title of the
file. It's context was in the <head> tagset, inside the <title>.
The <title> is the most specific structure, so it gets the
RANK_TITLE score: 7. The base rank of 1 plus the structure score of
7 equals 8. If there had been two instances of this word in the
title, then the score would have been "8 + 8 = 16".
IDF (1)
IDF is short for Inverse Document Frequency. That's fancy ranking
lingo for taking into account the total frequency of a term across
the entire index, in addition to the term's frequency in a single
document. IDF ranking also uses the relative density of a word in a
document to judge its relevancy. Words that appear more often in a
doc make that doc's rank higher, and longer docs are not weighted
higher than shorter docs.
The IDF Scheme might be summarized as:
DocRank = Sum of ( density * idf * ( structure + metabias ) )
Consider this output from DEBUG_RANK:
Ranking Scheme: 1
File num: 1104 Word Score: 1 Frequency: 8 Total files: 1451
Total word freq: 108 IDF: 2564
Total words: 1145877 Indexed words in this doc: 562
Average words: 789 Density: 1120 Word Weight: 28716
Word entry 0 at position 6 has struct 7
Word entry 1 at position 64 has struct 41
Word entry 2 at position 71 has struct 9
Word entry 3 at position 132 has struct 9
Word entry 4 at position 154 has struct 9
Word entry 5 at position 423 has struct 73
Word entry 6 at position 541 has struct 73
Word entry 7 at position 662 has struct 73
Rank after IDF weighting: 574321
scaled rank: 132609
Structure tally:
struct 0x7 = count of 1 ( HEAD TITLE FILE ) x rank map of 8 = 8
struct 0x9 = count of 3 ( BODY FILE ) x rank map of 1 = 3
struct 0x29 = count of 1 ( HEADING BODY FILE ) x rank map of 6 = 6
struct 0x49 = count of 3 ( EM BODY FILE ) x rank map of 1 = 3
It is similar to the default Scheme, but notice how the total num‐
ber of files in the index and the total word frequency (as opposed
to the document frequency) are both part of the equation.
Ranking is a complicated subject. SWISH-E allows for more Ranking
Schemes to be developed and experimented with, using the -R option
(from the swish-e command) and the RankScheme (see the API documenta‐
tion). Experiment and share your findings via the discussion list.
How can I limit searches to the title, body, or comment?
Use the "-t" switch.
I can't limit searches to title/body/comment.
Or, I can't search with meta names, all the names are indexed as
"plain".
Check in the config.h file if #define INDEXTAGS is set to 1. If it is,
change it to 0, recompile, and index again. When INDEXTAGS is 1, ALL
the tags are indexed as plain text, that is you index "title", "h1",
and so on, AND they loose their indexing meaning. If INDEXTAGS is set
to 0, you will still index meta tags and comments, unless you have
indicated otherwise in the user config file with the IndexComments
directive.
Also, check for the "UndefinedMetaTags" setting in your configuration
file.
I've tried running the included CGI script and I get a "Internal Server
Error"
Debugging CGI scripts are beyond the scope of this document. Internal
Server Error basically means "check the web server's log for an error
message", as it can mean a bad shebang (#!) line, a missing perl mod‐
ule, FTP transfer error, or simply an error in the program. The CGI
script swish.cgi in the example directory contains some debugging sug‐
gestions. Type "perldoc swish.cgi" for information.
There are also many, many CGI FAQs available on the Internet. A quick
web search should offer help. As a last resort you might ask your
webadmin for help...
When I try to view the swish.cgi page I see the contents of the Perl
program.
Your web server is not configured to run the program as a CGI script.
This problem is described in "perldoc swish.cgi".
How do I make Swish-e highlight words in search results?
Short answer:
Use the supplied swish.cgi or search.cgi scripts located in the example
directory.
Long answer:
Swish-e can't because it doesn't have access to the source documents
when returning results, of course. But a front-end program of your
creation can highlight terms. Your program can open up the source doc‐
uments and then use regular expressions to replace search terms with
highlighted or bolded words.
But, that will fail with all but the most simple source documents. For
HTML documents, for example, you must parse the document into words and
tags (and comments). A word you wish to highlight may span multiple
HTML tags, or be a word in a URL and you wish to highlight the entire
link text.
Perl modules such as HTML::Parser and XML::Parser make word extraction
possible. Next, you need to consider that Swish-e uses settings such
as WordCharacters, BeginCharacters, EndCharacters, IgnoreFirstChar, and
IgnoreLast, char to define a "word". That is, you can't consider that
a string of characters with white space on each side is a word.
Then things like TranslateCharacters, and HTML Entities may transform a
source word into something else, as far as Swish-e is concerned.
Finally, searches can be limited by metanames, so you may need to limit
your highlighting to only parts of the source document. Throw phrase
searches and stopwords into the equation and you can see that it's not
a trivial problem to solve.
All hope is not lost, thought, as Swish-e does provide some help.
Using the "-H" option it will return in the headers the current index
(or indexes) settings for WordCharacters (and others) required to parse
your source documents as it parses them during indexing, and will
return a "Parsed Words:" header that will show how it parsed the query
internally. If you use fuzzy indexing (word stemming, soundex, or
metaphone) then you will also need to stem each word in your document
before comparing with the "Parsed Words:" returned by Swish-e.
The Swish-e stemming code is available either by using the Swish-e Perl
module (SWISH::API) or the C library (included with the swish-e distri‐
bution), or by using the SWISH::Stemmer module available on CPAN. Also
on CPAN is the module Text::DoubleMetaphone. Using SWISH::API probably
provides the best stemming support.
Do filters effect the performance during search?
No. Filters (FileFilter or via "prog" method) are only used for build‐
ing the search index database. During search requests there will be no
filter calls.
I have read the FAQ but I still have questions about using Swish-e.
The Swish-e discussion list is the place to go. http://swish-e.org/.
Please do not email developers directly. The list is the best place to
ask questions.
Before you post please read QUESTIONS AND TROUBLESHOOTING located in
the INSTALL page. You should also search the Swish-e discussion list
archive which can be found on the swish-e web site.
In short, be sure to include in the following when asking for help.
* The swish-e version (./swish-e -V)
* What you are indexing (and perhaps a sample), and the number of files
* Your Swish-e configuration file
* Any error messages that Swish-e is reporting
Document Info
$Id: SWISH-FAQ.pod 2147 2008-07-21 02:48:55Z karpet $
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2.4.7 2009-04-04 SWISH-FAQ(1)
