DBD::Proxy is a Perl module for connecting to a database via a remote DBI driver.
This is of course not needed for DBI drivers which already
support connecting to a remote database, but there are engines which
don't offer network connectivity.
Another application is offering database access through a firewall, as
the driver offers query based restrictions. For example you can
restrict queries to exactly those that are used in a given CGI application.
Speaking of CGI, another application is (or rather, will be) to reduce
the database connect/disconnect overhead from CGI scripts by using
proxying the connect_cached method. The proxy server will hold the
database connections open in a cache. The CGI script then trades the
database connect/disconnect overhead for the DBD::Proxy connect/disconnect overhead which is typically much less.
Note that the connect_cached method is new and still experimental.
Before connecting to a remote database, you must ensure, that a Proxy
server is running on the remote machine. There's no default port, so
you have to ask your system administrator for the port number. See
the DBI::ProxyServer manpage for details.
Say, your Proxy server is running on machine ``alpha'', port 3334, and
you'd like to connect to an ODBC database called ``mydb'' as user ``joe''
with password ``hello''. When using DBD::ODBC directly, you'd do a
You see, this is mainly the same. The DBD::Proxy module will create a
connection to the Proxy server on ``alpha'' which in turn will connect
to the ODBC database.
perldoc2tree.cgi: /usr/lib/perl5/vendor_perl/5.8.8/i386-linux-thread-multi/DBD/Proxy.pm: cannot resolve L in paragraph 112.
Refer to the DBI documentation on the connect method for a way
to automatically use DBD::Proxy without having to change your code.
The value of this attribute will be used as a dsn name by the Proxy
server. Thus it must have the format DBI:driver:..., in particular
it will contain colons. The dsn value may contain semicolons, hence
this key *must* be the last and it's value will be the complete
remaining part of the dsn. Example:
By using these fields you can enable encryption. If you set,
for example,
cipher=$class;key=$key
(note the semicolon) then DBD::Proxy will create a new cipher object
by executing
$cipherRef = $class->new(pack("H*", $key));
and pass this object to the RPC::PlClient module when creating a
client. See the RPC::PlClient manpage. Example:
cipher=IDEA;key=97cd2375efa329aceef2098babdc9721
The usercipher/userkey attributes allow you to use two phase encryption:
The cipher/key encryption will be used in the login and authorisation
phase. Once the client is authorised, he will change to usercipher/userkey
encryption. Thus the cipher/key pair is a host based secret, typically less secure than the usercipher/userkey secret and readable by anyone.
The usercipher/userkey secret is your private secret.
Of course encryption requires an appropriately configured server. See
<DBD::ProxyServer/CONFIGURATION FILE>.
This attribute will set the corresponding attribute of the RPC::PlClient
object, thus logging will not use syslog(), but redirected to stderr.
This is the default under Windows.
The DBD::Proxy driver supports this attribute (which is DBI standard,
as of DBI 1.02). It's used to reduce network round-trips by fetching
multiple rows in one go. The current default value is 20, but this may
change.
This attribute can be used to reduce network traffic: If the
application is calling $sth->finish() then the proxy tells the server
to finish the remote statement handle. Of course this slows down things
quite a lot, but is prefectly good for reducing memory usage with
persistent connections.
However, if you set the proxy_no_finish attribute to a TRUE value,
either in the database handle or in the statement handle, then finish()
calls will be supressed. This is what you want, for example, in small
and fast CGI applications.
This attribute can be used to reduce network traffic: By default calls
to $dbh->quote() are passed to the remote driver. Of course this slows
down things quite a lot, but is the safest default behaviour.
However, if you set the proxy_quote attribute to the value 'local'
either in the database handle or in the statement handle, and the call
to quote has only one parameter, then the local default DBI quote
method will be used (which will be faster but may be wrong).
Sometimes handles are having complex attributes like hash refs or
array refs and not simple strings or integers. For example, with
DBD::CSV, you would like to write something like
The above example would advice the CSV driver to assume the file
``passwd'' to be in the format of the /etc/passwd file: Colons as
separators and a line feed without carriage return as line
terminator.
Surprisingly this example doesn't work with the proxy driver. To understand
the reasons, you should consider the following: The Perl compiler is
executing the above example in two steps:
The first step is fetching the value of the key ``csv_tables'' in the
handle $dbh. The value returned is complex, a hash ref.
The second step is storing some value (the right hand side of the
assignment) as the key ``passwd'' in the hash ref from step 1.
This becomes a little bit clearer, if we rewrite the above code:
While the examples work fine without the proxy, the fail due to a
subtile difference in step 1: By DBI magic, the hash ref
$dbh->{'csv_tables'} is returned from the server to the client.
The client creates a local copy. This local copy is the result of
step 1. In other words, step 2 modifies a local copy of the hash ref,
but not the server's hash ref.
The workaround is storing the modified local copy back to the server:
Jochen Wiedmann
Am Eisteich 9
72555 Metzingen
Germany
Email: joe@ispsoft.de
Phone: +49 7123 14887
The DBD::Proxy module is free software; you can redistribute it and/or
modify it under the same terms as Perl itself. In particular permission
is granted to Tim Bunce for distributing this as a part of the DBI.
perldoc2tree.cgi: /usr/lib/perl5/vendor_perl/5.8.8/i386-linux-thread-multi/DBD/Proxy.pm: cannot resolve L in paragraph 176.
perldoc2tree.cgi: /usr/lib/perl5/vendor_perl/5.8.8/i386-linux-thread-multi/DBD/Proxy.pm: cannot resolve L in paragraph 176.
