Mahendra M created LIBCLOUD-254:
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Summary: Provide generator based iteration instead of LazyList
Key: LIBCLOUD-254
URL: https://issues.apache.org/jira/browse/LIBCLOUD-254
Project: Libcloud
Issue Type: Improvement
Components: Core, Storage
Reporter: Mahendra M
Priority: Minor
LazyList was implemented by issue (LIBCLOUD-78) for more efficient iteration
over objects stored in a container (S3, CloudFiles etc. limit the maximum
number of objects returned in a single call).
LazyList solved this problem, but I think it might have the following issues
while handling containers with large number of objects
1) It loads the entire list to memory
2) caller has to wait for the entire list to be loaded in memory before any
operation can be done
3) The api invocation using get_more() and value_list is a bit complex (as-in,
it can be simplified)
By using python generators, the above two problems can be alleviated. Results
can be returned to the caller as and when it is returned from the server.
The following changes were done to the libcloud apis
1) A new api called - iterate_container_objects() was introduced. The storage
drivers need to implement this instead of list_container_objects(). This API
now returns a generator. Usage of this API will alleviate the above three
problems.
2) list_container_objects() will simply do -
list(self.iterate_container_objects(container)) - this is maintained for
backwards compatibility. It would be better if users can start using
iterate_**() api instead.
3) The same changes have been made for the DNS base class also.
4) LazyList() can be removed from libcloud if it is OK with everyone.
5) The generator based interface can be used (WIP) for providing paginated
access to objects - This will be useful for webpages/apps where the user has to
paginate through the results. The same can be implemented by providing
"start_key" and "count" parameters (similar to CouchDB) instead of generating
the entire list and then doing an offset. This will be more performance/memory
efficient than generating the entire list for every request.
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