On Thu, 23 Feb 2023 at 16:39, Kingsley Idehen
<kidehen(a)openlinksw.com>
wrote:
On 2/22/23 3:28 AM, Guillaume Lederrey wrote:
On Wed, 22 Feb 2023 at 00:03, Kingsley Idehen
via Wikidata
<wikidata(a)lists.wikimedia.org> wrote:
On 2/21/23 4:05 PM, Guillaume Lederrey wrote:
Hello all!
TL;DR: We expect to successfully complete the recent data
reload on
Wikidata Query Service soon, but we've
encountered multiple
failures
related to the size of the graph, and anticipate
that this
issue may
worsen in the future. Although we succeeded this
time, we
cannot
guarantee that future reload attempts will be
successful
given the
current trend of the data reload process. Thank
you for your
understanding and patience..
Longer version:
WDQS is updated from a stream of recent changes on
Wikidata, with a
maximum delay of ~2 minutes. This process was
improved as
part of the
WDQS Streaming Updater project to ensure data
coherence[1]
. However,
the update process is still imperfect and can
lead to data
inconsistencies in some cases[2][3]. To address this, we
reload the
data from dumps a few times per year to
reinitialize the
system from a
known good state.
The recent reload of data from dumps started in
mid-December and was
initially met with some issues related to
download and
instabilities
in Blazegraph, the database used by WDQS[4].
Loading the
data into
Blazegraph takes a couple of weeks due to the
size of the
graph, and
we had multiple attempts where the reload failed
after >90%
of the
data had been loaded. Our understanding of the
issue is
that a "race
condition" in Blazegraph[5], where subtle
timing changes
lead to
corruption of the journal in some rare cases, is
to blame.[6]
We want to reassure you that the last reload job was
successful on one
of our servers. The data still needs to be copied
over to
all of the
WDQS servers, which will take a couple of weeks,
but should
not bring
any additional issues. However, reloading the
full data
from dumps is
becoming more complex as the data size grows, and
we wanted
to let you
know why the process took longer than expected.
We
understand that
data inconsistencies can be problematic, and we
appreciate
your
patience and understanding while we work to
ensure the
quality and
Hi Guillaume,
Are there plans to decouple WDQS from the back-end database?
Doing that
provides more resilient architecture for Wikidata as a whole
since you
will be able to swap and interchange SPARQL-compliant backends.
It depends what you mean by decoupling. The coupling points as I
see them are:
* update process
* UI
* exposed SPARQL endpoint
The update process is mostly decoupled from the backend. It is
producing a stream of RDF updates that is backend independent,
with a very thin Blazegraph specific adapted to load the data
into Blazegraph.
Does that mean that we could integrate the RDF stream into our
setup re keeping our Wikidata instance up to date, for instance?
That data stream isn't exposed publicly. There are a few tricky part
about the stream needing to be synchronized with a specific Wikidata
dump that makes it not entirely trivial to reuse outside of our
internal use case. But if there is enough interest, we could
potentially work on making that stream public.