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



NAME
       DBD::Proxy - A proxy driver for the DBI

SYNOPSIS
         use DBI;

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

         # See the DBI module documentation for full details

DESCRIPTION
       DBD::Proxy is a Perl module for connecting to a database via a remote DBI driver. See DBD::Gofer for an alter-
       native with different trade-offs.

       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 restric-
       tions. 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
       experimental.

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

               hostname=alpha;port=3334

       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:

               dsn=DBI:ODBC:mydb

       cipher
       key
       usercipher
       userkey
           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 RPC::PlClient. 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 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 configured server. See <DBD::ProxyServer/CONFIGURATION
           FILE>.

       debug
           Turn on debugging mode

       stderr
           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.

               stderr=1

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

               logfile=/dev/null

       RowCacheSize
           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.

       proxy_no_finish
           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.

       proxy_quote
           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).

KNOWN ISSUES
       Unproxied method calls

       If a method isn't being proxied, try declaring a stub sub in the appropriate package (DBD::Proxy::db for a dbh
       method, and DBD::Proxy::st for an sth method).  For example:

           sub DBD::Proxy::db::selectall_arrayref;

       That will enable selectall_arrayref to be proxied.

       Currently many methods aren't explicitly proxied and so you get the DBI's default methods executed on the
       client.

       Some of those methods, like selectall_arrayref, may then call other methods that are proxied (selec-
       tall_arrayref calls fetchall_arrayref which calls fetch which is proxied). So things may appear to work but
       operate more slowly than the could.

       This may all change in a later version.

       Complex handle attributes

       Sometimes handles are having complex attributes like hash refs or array refs and not simple strings or inte-
       gers. For example, with DBD::CSV, you would like to write something like

         $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 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:

       1   The first step is fetching the value of the key "csv_tables" in the handle $dbh. The value returned is com-
           plex, 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 code:

         $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;

AUTHOR AND COPYRIGHT
       This module is Copyright (c) 1997, 1998

           Jochen Wiedmann
           Am Eisteich 9
           72555 Metzingen
           Germany

           Email: joeATispsoft.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.

SEE ALSO
       DBI, RPC::PlClient, Storable



perl v5.8.8                       2007-10-10                     DBD::Proxy(3)