As it was noted on the list, we recently tried to update Blazegraph -
software running Wikidata Query Service - to version 2.0, which has
numerous bugfixes and performance improvements, and some infrastructure
for future work on Geospatial search, etc.
Unfortunately, it seems, as it sometimes happens with new major
releases, that there are certain bugs in it, and yet more unfortunately,
one of the bugs seems to be of a race condition nature, which is very
hard to trigger on test environment, and that, when triggered, seriously
impacts the stability of the service. All this lead to WDQS service
being somewhat unstable last couple of days.
Due to this, I have rolled the production deployment back to pre-2.0
state. This means the service should be stable again and not experience
glitches anymore. I'll be watching it just in case and if you notice
anything that looks broken (like queries producing weird exceptions -
timeout does not count - or service being down, etc.) please ping me.
In the meantime, we will look for the cause of instability, and once it
is identified and fixed, we'll try the Blazegraph 2.0 roll-out again,
with the fixes applied. I'll send a note to the list when it happens.