Programming the Perl DBI

Compression

In the previous example, we discussed the possibility of a user querying the database via a modem line and proxy server. Suppose the user executes a query that returns 100,000 rows of data, each row being around 1 KB. That’s a lot of information to pull across a slow network connection.

To speed things up, you could configure the proxy server to use on-the-fly compression (via the Compress::Zlib module) to clients querying the database over dial-up connection. This will radically reduce the quantity of data being transferred across the modem link. You can do this by running the dbiproxy script with the additional arguments of:

--compression gzip

which specifies that the GNU gzip compression method should be used.

In order for your client to be able to send and receive compressed data from the DBI proxy server, you also must tell the proxy driver to use a compressed data stream. This is done by specifying the additional DSN key/value pair of compression=gzip when connecting to the database. For example:

$proxyloc = 'hostname=fowliswester;port=3333';
$compression = 'compression=gzip';
$dsn = 'dbi:ODBC:archaeo';
$dbh = DBI->connect( "dbi:Proxy:$proxyloc;$compression;dsn=$dsn", 
                     "username", "password" );

The trade-off is the cost in CPU time for the proxy server and proxy client to compress and decompress the data, respectively. From a client perspective, this is probably not an issue, but the proxy server might be affected, especially if several large queries are being executed ...