Set chunk size to 64 KB

Still, this is an arbitrary choice. But as send_long_data() is designed
to send out data to the network immediately, it is probably a good thing
performance-wise to have a little bit bigger chunks (think TCP windows
or offloading). And, on the other hand, 64 KB of memory in PHP should
not hurt that much.

lib/Doctrine/DBAL/Driver/Mysqli/MysqliStatement.php

@@ -257,7 +257,7 @@ private function _processLongData()
             if (is_resource($value) && get_resource_type($value) === 'stream') {
                 $stream = $value;
                 while (! feof($stream)) {
-                    $chunk = fread($stream, 8192);
+                    $chunk = fread($stream, 64 * 1024);
                     if ($chunk === false) {
                         throw new MysqliException("Failed processing the stream resource for parameter offset ${paramNr}.");
                     }