faq.pm

视频监控网络部分的协议ddns,的模块的实现代码,请大家大胆指正.

drivers or whether a driver is not fully compliant with the DBI Specification.

=item I<Rambles, Tidbits and Observations>

    http://dbi.perl.org/tidbits
    http://www.symbolstone.org/technology/perl/DBI/tidbits

There are a series of occasional rambles from various people on the
DBI mailing lists who, in an attempt to clear up a simple point, end up
drafting fairly comprehensive documents. These are quite often varying in
quality, but do provide some insights into the workings of the interfaces.

=item I<Articles>

A list of articles discussing the DBI can be found on the DBI WWW page at:

    http://dbi.perl.org/
    http://www.symbolstone.org/technology/perl/DBI

These articles are of varying quality and age, from the original Perl Journal
article written by Alligator and Tim, to more recent debacles published online
from about.com.

=item I<README files>

The I<README> files included with each driver occasionally contains 
some useful information ( no, really! ) that may be pertinent to the user.
Please read them. It makes our worthless existences more bearable. These
can all be read from the main DBI WWW page at:

    http://dbi.perl.org/
    http://www.symbolstone.org/technology/perl/DBI

=item I<Mailing Lists>

There are three mailing lists for DBI:

    [e-mail]     -- for announcements, very low traffic
    [e-mail]        -- general user support
    [e-mail]          -- for driver developers (no user support)

For information on how to subscribe, set digest mode etc, and unsubscribe,
send an email message (the content will be ignored) to:

    [e-mail]
    [e-mail]
    [e-mail]

=item I<Mailing List Archives>

=over 4

=item I<US Mailing List Archives>

    http://outside.organic.com/mail-archives/dbi-users/

Searchable hypermail archives of the three mailing lists, and some of the
much older traffic have been set up for users to browse.

=item I<European Mailing List Archives>

    http://www.rosat.mpe-garching.mpg.de/mailing-lists/PerlDB-Interest

As per the US archive above.

=back

=back

=head1 Compilation Problems

=head2 2.1. Compilation problems or "It fails the test!"

First off, consult the README for that driver in case there is useful 
information about the problem. It may be a known problem for your given 
architecture and operating system or database. You can check the README
files for each driver in advance online at:

    http://dbi.perl.org/
    http://www.symbolstone.org/technology/perl/DBI

If it's a known problem, you'll probably have to wait till it gets fixed. If 
you're I<really> needing it fixed, try the following:

=over 4

=item I<Attempt to fix it yourself>

This technique is generally I<not> recommended to the faint-hearted.
If you do think you have managed to fix it, then, send a patch file
( context diff ) to the author with an explanation of:

=over 4

=item *

What the problem was, and test cases, if possible.

=item *

What you needed to do to fix it. Please make sure you mention everything.

=item *

Platform information, database version, perl version, module version and 
DBI version.

=back

=item I<Email the author> Do I<NOT> whinge!

Please email the address listed in the WWW pages for whichever driver you
are having problems with. Do I<not> directly email the author at a
known address unless it corresponds with the one listed.

We tend to have real jobs to do, and we do read the mailing lists for
problems. Besides, we may not have access to <I<insert your
favourite brain-damaged platform here>> and couldn't be of any
assistance anyway! Apologies for sounding harsh, but that's the way of it!

However, you might catch one of these creative genii at 3am when we're
doing this sort of stuff anyway, and get a patch within 5 minutes. The
atmosphere in the DBI circle is that we I<do> appreciate the users'
problems, since we work in similar environments.

If you are planning to email the author, please furnish as much information
as possible, I<ie>:

=over 4

=item *

I<ALL> the information asked for in the README file in
the problematic module. And we mean I<ALL> of it. We don't
put lines like that in documentation for the good of our health, or
to meet obscure README file standards of length.

=item *

If you have a core dump, try the I<Devel::CoreStack> module for
generating a stack trace from the core dump. Send us that too.
I<Devel::CoreStack> can be found on CPAN at:

    http://www.perl.com/cgi-bin/cpan_mod?module=Devel::CoreStack

=item *

Module versions, perl version, test cases, operating system versions
and I<any other pertinent information>.

=back

Remember, the more information you send us, the quicker we can track 
problems down. If you send us no useful information, expect nothing back.

Finally, please be aware that some authors, including Tim Bunce, specifically
request that you do I<not> mail them directly. Please respect their wishes and
use the email addresses listed in the appropriate module C<README> file.

=item I<Email the dbi-users Mailing List>

It's usually a fairly intelligent idea to I<cc> the mailing list
anyway with problems. The authors all read the lists, so you lose nothing
by mailing there.

=back

=head1 Platform and Driver Issues

=head2 3.1 What's the difference between ODBC and DBI?

In terms of architecture - not much: Both define programming
interfaces. Both allow multiple drivers to be loaded to do the
actual work.

In terms of ease of use - much: The DBI is a 'high level' interface
that, like Perl itself, strives to make the simple things easy while
still making the hard things possible. The ODBC is a 'low level'
interface. All nuts-bolts-knobs-and-dials.

Now there's an ODBC driver for the DBI (DBD::ODBC) the "What's the
difference" question is more usefully rephrased as:

Chapter 7 of "Programming the Perl DBI" covers this topic in far more
detail and should be consulted.

=head2 3.2 What's the difference between Win32::ODBC and DBD::ODBC?

The DBI, and thus DBD::ODBC, has a different philosophy from the
Win32::ODBC module:

The Win32::ODBC module is a 'thin' layer over the low-level ODBC API.
The DBI defines a simpler 'higher level' interface.

The Win32::ODBC module gives you access to more of the ODBC API.
The DBI and DBD::ODBC give you access to only the essentials.
(But, unlike Win32::ODBC, the DBI and DBD::ODBC do support parameter
binding and multiple prepared statements which reduces the load on
the database server and can dramatically increase performance.)

The Win32::ODBC module only works on Win32 systems.
The DBI and DBD::ODBC are very portable and work on Win32 and Unix.

The DBI and DBD::ODBC modules are supplied as a standard part of the
Perl 5.004 binary distribution for Win32 (they don't work with the
older, non-standard, ActiveState port).

Scripts written with the DBI and DBD::ODBC are faster than Win32::ODBC
on Win32 and are trivially portable to other supported database types.

The DBI offers optional automatic printing or die()ing on errors which
makes applications simpler and more robust.

The current DBD::ODBC driver version 0.16 is new and not yet fully stable.
A new release is due soon [relative to the date of the next TPJ issue :-]
and will be much improved and offer more ODBC functionality.

To summarise: The Win32::ODBC module is your best choice if you need
access to more of the ODBC API than the DBI gives you. Otherwise, the
DBI and DBD::ODBC combination may be your best bet.

Chapter 7 of "Programming the Perl DBI" covers this topic in far more
detail and should be consulted.

=head2 3.3 Is DBI supported under Windows 95 / NT platforms?

Finally, yes! Jeff Urlwin has been working diligently on building
I<DBI> and I<DBD::ODBC> under these platforms, and, with the
advent of a stabler perl and a port of I<MakeMaker>, the project has
come on by great leaps and bounds.

The I<DBI> and I<DBD::Oracle> Win32 ports are now a standard part of DBI,
so, downloading I<DBI> of version higher than I<0.81> should work fine as 
should using the most recent I<DBD::Oracle> version.

=head2 3.4 Can I access Microsoft Access or SQL-Server databases with DBI?

Yes, use the I<DBD::ODBC> driver.

=head2 3.5 Is the a DBD for <I<insert favourite database here>>?

Is is listed on the DBI drivers page?

    http://dbi.perl.org/
    http://www.symbolstone.org/technology/perl/DBI

If not, no. A complete absence of a given database driver from that
page means that no-one has announced any intention to work on it, not that
such a driver is impossible to write.

A corollary of the above statement implies that if you see an announcement
for a driver I<not> on the above page, there's a good chance it's not
actually a I<DBI> driver, and may not conform to the specifications. Therefore,
questions concerning problems with that code should I<not> really be addressed
to the DBI Mailing Lists.

=head2 3.6 What's DBM? And why should I use DBI instead?

Extracted from ``I<DBI - The Database Interface for Perl 5>'':

    ``UNIX was originally blessed with simple file-based ``databases'', namely
    the dbm system. dbm lets you store data in files, and retrieve
    that data quickly. However, it also has serious drawbacks.

        File Locking

        The dbm systems did not allow particularly robust file locking
        capabilities, nor any capability for correcting problems arising through
        simultaneous writes [ to the database ].

        Arbitrary Data Structures

        The dbm systems only allows a single fixed data structure:
        key-value pairs. That value could be a complex object, such as a
        [ C ] struct, but the key had to be unique. This was a large
        limitation on the usefulness of dbm systems.

    However, dbm systems still provide a useful function for users with
    simple datasets and limited resources, since they are fast, robust and 
    extremely well-tested. Perl modules to access dbm systems have now
    been integrated into the core Perl distribution via the
    AnyDBM_File module.''

To sum up, DBM is a perfectly satisfactory solution for essentially read-only
databases, or small and simple datasets. However, for more 
scaleable dataset handling, not to mention robust transactional locking, 
users are recommended to use a more powerful database engine I<via> I<DBI>.

Chapter 2 of "Programming the Perl DBI" discusses DBM files in detail.

=head2 3.7 What database do you recommend me using?

This is a particularly thorny area in which an objective answer is difficult
to come by, since each dataset, proposed usage and system configuration
differs from person to person.

From the current author's point of view, if the dataset is relatively
small, being tables of less than 1 million rows, and less than 1000 tables
in a given database, then I<mSQL> is a perfectly acceptable solution
to your problem. This database is extremely cheap, is wonderfully robust
and has excellent support. More information is available on the Hughes
Technology WWW site at:

    http://www.hughes.com.au

You may also wish to look at MySQL which is a more powerful database engine
that has a similar feel to mSQL.

    http://www.tcx.se

If the dataset is larger than 1 million row tables or 1000 tables, or if you
have either more money, or larger machines, I would recommend I<Oracle RDBMS>.
Oracle's WWW site is an excellent source of more information.

    http://www.oracle.com

I<Informix> is another high-end RDBMS that is worth considering. There are
several differences between Oracle and Informix which are too complex for
this document to detail. Information on Informix can be found on their
WWW site at:

    http://www.informix.com

In the case of WWW fronted applications, I<mSQL> may be a better option
due to slow connection times between a CGI script and the Oracle RDBMS and