On Tue, Nov 15, 2011 at 5:26 PM, Ewan Mellor <ewan.mel...@eu.citrix.com> wrote: >> From: Ewan Mellor >> > From: Jay Pipes [mailto:jaypi...@gmail.com] >> > > From: Ewan Mellor >> > > ~ # cat test_glance.py >> > > import sys >> > > import glance.client >> > > >> > > client = glance.client.Client('localhost', 9292, >> > auth_tok="999888777666") >> > > print client.add_image({}, sys.stdin) >> > > ~ # echo a | python26 ./test_glance.py >> > > {u'status': u'active', u'name': None, u'deleted': False, >> > u'container_format': None, u'created_at': u'2011-11-15T21:44:21', >> > u'disk_format': None, u'updated_at': u'2011-11-15T21:44:22', u'id': >> 6, >> > u'owner': u'Administrator', u'location': >> > u'swift+http://root:password@localhost:5000/v1.0/glance/6', >> u'min_ram': >> > 0, u'checksum': u'60b725f10c9c85c70d97880dfe8191b3', u'min_disk': 0, >> > u'is_public': False, u'deleted_at': None, u'properties': {}, u'size': >> > 0} >> > > >> > > Note that size is returned as 0, not 1. >> > >> > Yes, indeed. That is because the client is not designed to be used >> > that way [snip] >> >> But it could perfectly well be used this way, modulo the bug above, and >> this is a very useful thing to be able to do (stdin here could be a >> decompression or decryption pipeline, or a read from a remote socket, >> or >> whatever. >> >> With the bug in the Swift backend fixed, I think it will work just fine >> to stream through a glance client in this way. > > Erm, well it will until we hit the 5GB Swift chunking limit, anyway. > > Do you know what this means (glance/store/swift.py +347)? > Why can't we stream from body_file? > > else: > # Write the image into Swift in chunks. We cannot > # stream chunks of the webob.Request.body_file, unfortunately, > # so we must write chunks of the body_file into a temporary > # disk buffer, and then pass this disk buffer to Swift.
We can (and we do in the case when image_size=0 when calling the Swift backend store's add() method). Unfortunately, since you don't know the file size, you begin streaming to Swift (essentially by passing body_file on to the swift.client.Connection.put_object() method). Unfortunately, if the file is >5GB, what will happen is that Swift will vomit after attempting to upload 5G of data, resulting in a situation where the Glance Swift storage driver would then have to try to restart the upload using a segmented approach. But in order to do that, the driver would have to seek(0) back on the body_file. However, by default, webob.Request.body_file is NOT seekable. To make it seekable, you need to either do this: webob.Request.make_body_seekable() or this: webob.Request.is_body_seekable = True Unfortunately, doing either of the above results in the entire request body being buffered to disk on the server side in order for webob to convert the (unseekable) StringIO it uses for webob.Request.body into a (seekable) regular file object that it then assigns to its webob.Request.body_file attribute. So, let's say we tried to handle re-trying a segmented upload after we first try to upload a 6GB image file *without* setting the image_size to the actual size. What would happen is this: Write 5GB of data to the swift socket Get error, make body_file seekable in order to seek(0) back to the request body's starting point, which results in copying the entire body_file (6GB) into a temporary file on the server seek(SEEK_END) on that body_file to get the real image size, and then stream 6GB of data in chunks to Swift using its segmented upload method. Total data written to disk and network for 6GB image file: 5GB + 6GB + 6GB = 17GB Or you can set the image_size properly by determining the file size ahead of time. :) You can read more about this issue here: https://bugs.launchpad.net/glance/+bug/794718 https://bugs.launchpad.net/glance/+bug/818292 upstream: https://bitbucket.org/ianb/webob/issue/12/fix-for-issue-6-broke-chunked-transfer Cheers, -jay _______________________________________________ Mailing list: https://launchpad.net/~openstack Post to : openstack@lists.launchpad.net Unsubscribe : https://launchpad.net/~openstack More help : https://help.launchpad.net/ListHelp
