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 alternative 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 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.
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 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>.
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 perfectly 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 (selectall_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 integers. 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 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 code:
$tables = $dbh->{"csv_tables"};
$tables->{"passwd"} = { "sep_char" => ":", "eol" => "\n";
While the examples work fine without the proxy, the fail due to a
subtle 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;
SECURITY WARNING
RPC::PlClient used underneath is not secure due to serializing and
deserializing data with Storable module. Use the proxy driver only in
trusted environment.
AUTHOR AND COPYRIGHT
This module is Copyright (c) 1997, 1998
Jochen Wiedmann
Am Eisteich 9
72555 Metzingen
Germany
Email: joe AT 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.
SEE ALSO
DBI, RPC::PlClient, Storable
perl v5.16.3 2014-06-10 DBD::Proxy(3)