openstack/swift
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Add comment about ResumingGetter.used_source_etag

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This confused a couple developers and took about ten minutes to
unravel in IRC; let's leave a clue for the next person.

Change-Id: I356c8c7a44de23f02eaf68d23a39c9eb4c203ff1
This commit is contained in:
Samuel Merritt 2015-07-20 17:03:20 -07:00
parent 317fa1af49
commit c3cc98b2c9
1 changed files with 7 additions and 0 deletions
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7
swift/proxy/controllers/base.py
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@ -1045,6 +1045,13 @@ class ResumingGetter(object):
src_headers = dict(
(k.lower(), v) for k, v in
possible_source.getheaders())
# Save off the source etag so that, if we lose the connection
# and have to resume from a different node, we can be sure that
# we have the same object (replication) or a fragment archive
# from the same object (EC). Otherwise, if the cluster has two
# versions of the same object, we might end up switching between
# old and new mid-stream and giving garbage to the client.
self.used_source_etag = src_headers.get(
'x-object-sysmeta-ec-etag',
src_headers.get('etag', '')).strip('"')