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DBD::Proxy(3)  User Contributed Perl Documentation  DBD::Proxy(3)

       DBD::Proxy - A proxy driver for the DBI

         use DBI;

         $dbh = DBI->connect("dbi:Proxy:hostname=$host;port=$port;dsn=$db",
                             $user, $passwd);

         # See the DBI module documentation for full details

       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 connec-
       tions 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

       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 DBI::ProxyServer(3)
       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

         $dbh = DBI->connect("DBI:ODBC:mydb", "joe", "hello");

       With DBD::Proxy this becomes

         $dsn = "DBI:Proxy:hostname=alpha;port=3334;dsn=DBI:ODBC:mydb";
         $dbh = DBI->connect($dsn, "joe", "hello");

       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.

       Refer to the DBI(3) documentation on the "connect" method
       for a way to automatically use DBD::Proxy without having
       to change your code.

       DBD::Proxy's DSN string has the format

         $dsn = "DBI:Proxy:key1=val1; ... ;keyN=valN;dsn=valDSN";

       In other words, it is a collection of key/value pairs. The
       following keys are recognized:

           Hostname and port of the Proxy server; these keys must
           be present, no defaults. Example:


       dsn 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,


           (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 RPC::PlClient(3). Example:


           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 userci-
           pher/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 config-
           ured server. See DBD::ProxyServer(3)/CONFIGURATION

           Turn on debugging mode

           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.


           Similar to the stderr attribute, but output will be
           redirected to the given file.


           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

           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).

       Complex handle attributes

       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

         $dbh->{"csv_tables"}->{"passwd"} =
               { "sep_char" => ":", "eol" => "\n";

       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 car-
       riage 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 exam-
       ple in two steps:

       1.) The first step is fetching the value of the key
           "csv_tables" in the handle $dbh. The value returned is
           complex, a hash ref.

       2.) 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

         $tables = $dbh->{"csv_tables"};
         $tables->{"passwd"} = { "sep_char" => ":", "eol" => "\n";

       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:

         $tables = $dbh->{"csv_tables"};
         $tables->{"passwd"} = { "sep_char" => ":", "eol" => "\n";
         $dbh->{"csv_tables"} = $tables;

       This module is Copyright (c) 1997, 1998

           Jochen Wiedmann
           Am Eisteich 9
           72555 Metzingen

           Phone: +49 7123 14887

       The DBD::Proxy module is free software; you can redis-
       tribute 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.

       DBI(3), RPC::PlClient(3), Storable(3)

perl v5.6.1                 2002-01-21              DBD::Proxy(3)

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