On 19.04.2016 11:05, Addshore wrote:
In the case we are discussing here the truncated JSON
is caused by blaze
graph deciding it has been sending data for too long and then stopping
(as I understand).
Thus you will only see a spike on the graph for the amount of data
actually sent from the server, not the size of the result blazegraph was
trying to send back.
I successfully got five files of 250M JSON each, but even those
successful queries did not show up in the stats. The five files had
three different versions (slightly different sizes) so they did not all
come from a common cache either. Maybe the size is counted in terms of
compressed or otherwise "raw" results?
I also ran into this with some simple queries that returned big sets of
data.
Although with my issue I did actually also see a Java exception somewhere.
I know the case where large result sets end in a Java timeout exception.
This occurs reproducibly when you retrieve all humans or something like
that. However, in my case, the behaviour is not always reproducible and
there is no Java exception at the end of the output; it just stops in
the middle of the file.
Markus
On 18 April 2016 at 21:51, Markus Kroetzsch
<markus.kroetzsch(a)tu-dresden.de <mailto:markus.kroetzsch@tu-dresden.de>>
wrote:
On 18.04.2016 22:21, Markus Kroetzsch wrote:
On 18.04.2016 21:56, Markus Kroetzsch wrote:
Thanks, the dashboard is interesting.
I am trying to run this query:
SELECT ?subC ?supC WHERE { ?subC p:P279/ps:P279 ?supC }
It is supposed to return a large result set. But I am only
running it
once per week. It used to work fine, but today I could not
get it to
succeed a single time.
Actually, the query seems to work as it should. I am
investigating why I
get an error in some cases on my machine.
Ok, I found that this is not so easy to reproduce reliably. The
symptom I am seeing is a truncated JSON response, which just stops
in the middle of the data (at a random location, but usually early
on), and which is *not* followed by any error message. The stream
just ends.
So far, I could only get this in Java, not in Python, and it does
not always happen. If successful, the result is about 250M in size.
The following Python script can retrieve it:
import requests
SPARQL_SERVICE_URL = 'https://query.wikidata.org/sparql'
query = """SELECT ?subC ?supC WHERE { ?subC p:P279/ps:P279 ?supC
}"""
print requests.get(SPARQL_SERVICE_URL, params={'query': query,
'format': 'json'}).text
(output should be redirected to a file)
I will keep an eye on the issue, but I don't know how to debug this
any further now, since it started to work without me changing any code.
I also wonder how to read the dashboard after all. In spite of me
repeating an experiment that creates a 250M result file for five
times in the past few minutes, the "Bytes out" figure remains below
a few MB for most of the time.
Markus
On 18.04.2016 21:40, Stas Malyshev wrote:
Hi!
I have the impression that some not-so-easy SPARQL
queries that used to
run just below the timeout are now timing out
regularly. Has there been
a change in the setup that may have caused this, or
are we maybe seeing
increased query traffic [1]?
We've recently run on a single server for couple of days
due to
reloading of the second one, so this may have made it a
bit slower. But
that should be gone now, we're back to two. Other than
that, not seeing
anything abnormal in
https://grafana.wikimedia.org/dashboard/db/wikidata-query-service
[1] The deadline for the Int. Semantic Web Conf. is
coming up, so it
might be that someone is running experiments on the
system to get their
paper finished. It has been observed for other
endpoints that traffic
increases at such times. This community sometimes is
the greatest enemy
of its own technology ... (I recently had to
IP-block an RDF crawler
from one of my sites after it had ignored robots.txt
completely).
We don't have any blocks or throttle mechanisms right
now. But if we see
somebody making serious negative impact on the service,
we may have to
change that.
--
Markus Kroetzsch
Faculty of Computer Science
Technische Universität Dresden
+49 351 463 38486 <tel:%2B49%20351%20463%2038486>
http://korrekt.org/
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Addshore
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