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From Andy Seaborne <a...@apache.org>
Subject Re: AW: AW: AW: Error 500: No conversion to a Node: <RDF_Term >
Date Mon, 11 Mar 2019 21:59:15 GMT
Hi Andreas,

On 11/03/2019 14:37, Walker, Andreas wrote:
> Hi Andy,
> 
> 
> the database was created from the web interface, and I've only used the web interface
to add data to it, so no other version has ever touched it.

OK - so you have only run v3.10.0.

> If I understand you correctly, the problem is with the database as a whole, so dropping
and reloading the graph might not solve the problem. I have now switched to a fresh database
and am currently reloading the data, so I can see whether the problem persists beyond the
original database.

If it does then we have a reproducible test case.  That said, I can 
think of a way of a single load or a single load and a sequence of 
updates not in a parallel can break the node table.

The email of Osma's is a compaction - have you compacted the database? 
(Fuseki must not be running at the time - this is supposed to be caught 
using OS file locks but ... I'm told VMs can get this wrong (but I don't 
know which and when).

> The only backup I have done is by making snapshots of the entire virtual server this
is running on, so I don't think that is related in any way.

Probably not related but is it an instantaneous backup of the 
filesystem? If not, then it isn't a reliable backup (in the same way 
that copying all the files isn't a safe backup procedure).

The problem is that if the copy is done while a write transaction is 
running, some files may be copied before the commit point and some 
after, which risks chaos.

     Andy

> 
> 
> Thanks again for your help,
> 
> Andreas
> 
> ________________________________
> Von: Andy Seaborne <andy@apache.org>
> Gesendet: Freitag, 8. März 2019 10:50:28
> An: users@jena.apache.org
> Betreff: Re: AW: AW: Error 500: No conversion to a Node: <RDF_Term >
> 
> Hi Andreas,
> 
> Is this a database that has only ever been used with 3.10.0 or was the
> data loaded with a previous version at some time in the past?
> 
> The problem occurs silently during loading. There is no sign of the
> problem at the time and the system works just fine while the RDF term,
> or terms, are also in the node table cache.
> 
> Then the system is restarted.
> 
> Then the RDF term is needed for a query and the errors are reported.
> 
> But the problem originated back when the data was loaded or updated, may
> be several restarts ago.
> 
> Of course, it may be a different issue in which case, but the error
> message is consistent with the known bug.
> 
> Have you been backing up the server on a regular basis? A backup is
> NQuads so it is pulling every RDF term from disk (subject to already
> being cached).
> 
>       Andy
> 
> On 07/03/2019 20:47, Walker, Andreas wrote:
>> Hi Andy,
>>
>>
>> I am running Version 3.10.0. The problem with reloading the database is the regular
(multiple times a day) recurrence of the problem, so if there are any strategies to avoid
it, I'd appreciate any advice.
>>
>>
>> Best,
>>
>> Andreas
>>
>>
>> ________________________________
>> Von: Andy Seaborne <andy@apache.org>
>> Gesendet: Donnerstag, 7. März 2019 21:12
>> An: users@jena.apache.org
>> Betreff: Re: AW: Error 500: No conversion to a Node: <RDF_Term >
>>
>> Hi Andreas - which version are you running?
>>
>> It does not look like the  corruption problem, which is now fixed.
>>
>> The best thing to do is reload the database again. Whatever terms were
>> messed up are permanently damaged I'm afraid.
>>
>>        Andy
>>
>> On 07/03/2019 10:49, Walker, Andreas wrote:
>>> Dear all,
>>>
>>>
>>> as a quick follow-up which might be helpful in identifying the error; I can currently
run a SPARQL query (just listing any triples) with LIMIT 80, but no higher, before I run into
the error, so it seems like there might indeed be a particular part of the database that is
corrupted.
>>>
>>>
>>> Best,
>>>
>>> Andreas
>>>
>>> ________________________________
>>> Von: Walker, Andreas <andreas.walker@sub.uni-goettingen.de>
>>> Gesendet: Mittwoch, 6. März 2019 10:42:32
>>> An: users@jena.apache.org
>>> Betreff: Error 500: No conversion to a Node: <RDF_Term >
>>>
>>> Dear all,
>>>
>>>
>>> from time to time, my Fuseki server starts throwing the following error message
on any SPARQL query I pose to one of my graphs:
>>>
>>>
>>> "Error 500: No conversion to a Node: <RDF_Term >"
>>>
>>>
>>> Unfortunately, I couldn't find any explanation of this error message, beyond
a discussion of a corrupted TDB2 database.
>>>
>>>
>>> (https://users.jena.apache.narkive.com/LF4XE801/corrupted-tdb2-database)<https://users.jena.apache.narkive.com/LF4XE801/corrupted-tdb2-database>
>>>
>>>
>>> Once this happens, the only thing I could do so far is to drop the entire afflicted
graph and rebuild it, but of course that isn't going to be a viable solution in the long term.
>>>
>>>
>>> The only way I interact with Fuseki is by starting and stopping it, querying
it via the SPARQL endpoint (and sometimes through the web interface, e.g. when troubleshooting
my application), and uploading new triples (as turtle files) via the web interface. I haven't
been able to find a pattern in when the error appears so far.
>>>
>>>
>>> Any insights into why this error appears, and what to do in order to avoid it?
I'd appreciate any help.
>>>
>>>
>>> Best,
>>>
>>> Andreas
>>>
>>
> 

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