[Zope] should stream iterator be used for ZODB-generated string file?

[Petri Savolainen]

We have an application whereby multimegabyte strings, each generated 
from the contents of several thousands of small objects in ZODB, are 
downloaded from zope as a CSV files. A particular CSV file is typically 
downloaded once or twice a day at a maximum.

The major issue is that it takes a long time for the download to start. 
Would it be possible to use a stream iterator (introduced in zope 2.7.1) 
or should we simply do chunks of REQUEST.write() ? What are the 
requirements for using chunked REQUEST.write - do some specific HTTP 
headers need to be set or does zope take care of it all?

Any advice or specific pointers would be appreciated. I've googled all I 
could find about the stream iterators, serving blobs etc. but all the 
info seems to be focused on serving large filesystem-based data. I am 
not sure what parts of that info applies to an use case that involves 
reading data from ZODB, or if stream iterators make sense for the use 
case at all.

I guess we could generate a temporary file and then serve that using a 
stream iterator. I understand some parts of the zope machinery could 
perhaps be released faster that way, but I wonder if the benefits are 
worth the extra step.

Thanks!

  Petri