https://bugzilla.wikimedia.org/show_bug.cgi?id=34695

Ben Hartshorne <[email protected]> changed:

           What    |Removed                     |Added
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             Status|NEW                         |ASSIGNED

--- Comment #3 from Ben Hartshorne <[email protected]> 2012-02-24 
22:35:28 UTC ---
The initial run to purge broken thumbnails reduced our incidence from about
1.5% of all thumbnails to 0.003%, but I believe there are still a few left.  I
am currently working on a slow process to cull the rest (this will likely run
for at least 2 weeks to complete).  Though it will take a long time I think
it's ok given the low incidence. 

Re: Ralf's comment "what makes you think you solved the problem?": we were able
to recreate the issue by initiating a connection to swift requesting a
thumbnail that doens't alraedy exist and closing the connection before the
entire thumbnail is returned.  Closing the client side early resulted in a
truncated file getting written to Swift.  We adjusted the code in Swift to pay
attention to the Content-Length header and the ETag headers (if they exist) and
at the same time adjusted the code on ms5 (Swift's current backend) and the
image scalers to create content-length and ETag headers whenever possible. 
After making these changes, closing the client connection prematurely resulted
in nothing getting written to Swift instead of a truncated image.  The PUT to
swift would fail because the closed connection meant that the data pushed into
the system did not match whichever headers were available.  

While we can never be absolutely sure that a different bug with the same
symptoms doesn't also exist, all my tests so far have been unable to recreate
truncated images in Swift.  Additionally, I installed a process to monitor
roughly 30% of all newly created Swift objects and check them against the copy
on ms5 to identify any new incidence of the same (or similar) bugs.  This
monitoring process hasn't seen any truncated images appear since we deployed
the fix to the dropped connection bug.

The files referenced in this bug (the Commons emblem) was created truncated in
swift prior to the deploy of the fix for the dropped connection bug, so is a
left over remnant rather than a new example.  

I'll close this bug when the final cleanup of the remaining broken thumbnails
is complete.

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