SUMMARY: This week I experienced an issue when uploading several
hundred very high resolution maps as part the NYPL maps project.[1]
Discussion has been going on in several places and this thread is an
attempt to share a discussion in one place so all users can benefit.
[Gilles, Could you join this low volume open email list to keep track
of GWT issues and be a voice for WMF Operations to help us reach a
recommendation for end user best practices?]
HISTORY
For our GLAM projects my upload was unusually stressful for the WMF
servers. Individual map scans are up to 300 MB images, and resolutions
can exceed 80 megapixels (80 million pixels). There are 20,000 tiff
images to be uploaded, I have completed around 12%. I used the
GLAMtoolset at full capacity (20 threads) though I had broken the xml
file up, so runs were a few hundred images at a time. My intention was
to ramp this up to a couple of thousand per upload "tranche".
I was contacted on Tuesday by operations asking for me to suspend the
upload as the demand for attempted thumbnail rendering of the tiff
images was too high a load on WMF servers.[2] Over 500 of the tiff
images were greater than 50 megapixels and as a consequence Commons
fails to render any thumbnails (they are created for jpegs greater
than this limit, this is a tiff specific constraint).[3]
CURRENT STATE
With no obvious immediate fix/work-around on the table from WMF ops, I
have proposed to re-start my uploads for this project with an
effective throttle by using 2 threads (this is a setting on the first
screen of the GWToolset. In practice, having tried a run of a couple
of hundred, this means that the tool is uploading 100MB sized images
at a rate of 2 every 5 minutes. This seems to not be causing any
issues.
WAY FORWARD
In the longer term the WMF is looking at alternatives for rendering
tiff thumbnails which will enable 50MP+ images to be handled; this may
or may not help solve the problem seen this week.[4]
I recommend that the GWToolset on-wiki guides include a recommendation
about how to choose the number of processing threads based on the
types of images to be uploaded. To date, no other project has seen
these problems, probably because the image resolutions fall well under
the 50MP threshold. The maximum allowed number of threads is 20, with
a default being 10. For the time being I suggest that we agree a best
practice that for upload projects with tiffs over 50MP, that no more
than 2 threads are used; these problems do not appear to exist for
projects uploading smaller resolution files.
I propose that WMF Operations consider finding ways of testing the
peak loads possible from the GWT and decide if this can be fixed by
future operational improvements, whether the tool might benefit from
some simple "load management" changes, or if establishing a best
practice for our (relatively) small number of GWT users would be a
sufficient community based control.
Links
1.
https://commons.wikimedia.org/wiki/Commons:Batch_uploading/NYPL_Maps
2.
https://commons.wikimedia.org/wiki/Commons_talk:Batch_uploading/NYPL_Maps
3.
https://commons.wikimedia.org/wiki/Category:NYPL_maps_%28over_50_megapixels…
4.
https://bugzilla.wikimedia.org/show_bug.cgi?id=52045
Fae
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faewik(a)gmail.com
https://commons.wikimedia.org/wiki/User:Fae