Webform is a great module and I use it on several customer sites. One customer has a Site with a Form for registering for a competition. By end of the registration period there are 74000 entries.
When I try to download all 74000 results at once I always get the PHP-Error message:
Fatal error: Allowed memory size of 1073741824 bytes exhausted (tried to allocate 72 bytes) in .../sites/all/modules/webform/includes/webform.submissions.inc on line 664
As you can see I allready gave PHP 1024M memory, which should not be the normal value for a Drupal site.
As of Version 6.x-3.13 I can download a specific range of submissions, thank you very much for that ;-))
The Form collects quit some data: for 10000 entries the resultung text file is about 4MB big. So 40000 results are about 16MB in the text file.
As my customer blames me for this behaviour I should mark this as a bug report. But I think the module is working fine so I mark it as a feature request. I really wuold like to see an optimized version for many many results. Maybe its also a good idea to zip the results before downloading it.