Re: [Virtuoso-users] checkpointSyncMode default value

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HI Balazs,

I tried your test case below of running checkpoint in a loop and then running the curl command, which quite  intermittently gives the error:

$ curl -G http://demo.openlinksw.com --data-urlencode graph=http://www.w3.org/2002/07/owl#
<html>
    <head>
	<title>Web Site Under Maintenance</title>
	<META HTTP-EQUIV="CACHE-CONTROL" CONTENT="NO-CACHE">
	<META HTTP-EQUIV="PRAGMA" CONTENT="NO-CACHE">
    </head>
    <body>
	<div><img src="data:image/gif;base64,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" style="float:left;"/>
	    <div style="font-weight: bold; font-size:18px; font-family: verdana;">
		The web-site you are currently trying to access is under maintenance at this time. <br/>
		We are sorry for any inconvenience this might cause.</div></div>
    </body>
$ 

which is what I would expect when the database is in atomic mode during the checkpoint ...

Best Regards
Hugh Williams
Professional Services
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Universal Data Access, Integration, and Management Technology Providers

> On 29 Jul 2016, at 12:47, Balazs Varhegyi <var...@gm...> wrote:
> 
> Hi Hugh,
> 
> It seems like what Lorenz said: 
> 
> Without the doing the checkpoint this curl works: "curl -G http://localhost:8890/sparql-graph-crud <http://localhost:8890/sparql-graph-crud>      --data-urlencode graph=http://www.w3.org/2002/07/owl# <http://www.w3.org/2002/07/owl#>"
> but as soon as I start doing checkpoints in an infinite-loop. Curl response turns to:
> 
> <html>
>   <head>
>     <title>Error HTTP/1.1 404 File not found</title>
>   </head>
>   <body>
>     <h3>Error HTTP/1.1 404 File not found</h3>
>     <pre>The requested URL was not found    URI  = '/sparql-graph-crud' </pre>
>   </body>
> </html>
> 
> Still no error in virtuoso.log with the settings you provided.
> 
> Regards, 
> Balazs
> 
> On 29/07/16 14:05, Balazs Varhegyi wrote:
>> Hi,
>> 
>> Hugh, I set the provided parameters but I see only the log of the successful checkpoint. No errors in virtuoso.log.
>> 
>> Regards,
>> Balazs
>> 
>> On 29/07/16 11:09, Lorenz Buehmann wrote:
>>> Hi Hugh,
>>> 
>>> 
>>> I guess Jena gets no connection to the SPARQL service at the time Virtuoso is temporarily inaccessible
>>> 
>>> and thus simply returns a 404 error.
>>> 
>>> 
>>> Cheers,
>>> 
>>> Lorenz
>>> 
>>> On 28.07.2016 15:03, Hugh Williams wrote:
>>>> Hi Balazs,
>>>> 
>>>> >From your stackoverflow post the “com.hp.hpl.jena.sparql.engine.http.QueryExceptionHTTP: File not found” error is coming from Jena, are any error in the Virtuoso log ? When performing a checkpoint which is an atomic action in Virtuoso the database will be temporarily inaccessible and a "40001 Error SR172: Transaction deadlocked” error or similar would be returned, thus a client application should handle such conditions as when handling deadlocks generally. Thus are any error being reported when this error occurs in Jena, in the “virtuoso.log” file ?
>>>> 
>>>> Can you set the following params in the "[Parameters]" section of the INI file and restart the server which should enabled more detailed client errors to be returned if occurring
>>>> 
>>>> 	CallstackOnException =  2
>>>> 	PLDebug = 1 
>>>> 
>>>> Best Regards
>>>> Hugh Williams
>>>> Professional Services
>>>> OpenLink Software, Inc.      //              http://www.openlinksw.com/ <http://www.openlinksw.com/>
>>>> Weblog   -- http://www.openlinksw.com/blogs/ <http://www.openlinksw.com/blogs/>
>>>> LinkedIn -- http://www.linkedin.com/company/openlink-software/ <http://www.linkedin.com/company/openlink-software/>
>>>> Twitter  -- http://twitter.com/OpenLink <http://twitter.com/OpenLink>
>>>> Google+  -- http://plus.google.com/100570109519069333827/ <http://plus.google.com/100570109519069333827/>
>>>> Facebook -- http://www.facebook.com/OpenLinkSoftware <http://www.facebook.com/OpenLinkSoftware>
>>>> Universal Data Access, Integration, and Management Technology Providers
>>>> 
>>>>> On 25 Jul 2016, at 10:37, Balazs Varhegyi <var...@gm...> <mailto:var...@gm...> wrote:
>>>>> 
>>>>> Ok, I managed to get this exception when CheckpointSynchMode is 1. 
>>>>> So when I do a query that only reads virtuoso when it does the checkpoint is  causes this com.hp.hpl.jena.sparql.engine.http.QueryExceptionHTTP, why?
>>>>> 
>>>>> Regards, Balazs
>>>>> 
>>>>> On 22/07/16 15:44, Balazs Varhegyi wrote:
>>>>>> Hi,
>>>>>> 
>>>>>> Why CheckpointSyncMode is 2 by default? 
>>>>>> What happens if we set this value to 1?
>>>>>> I found "CheckpointSyncMode" section in this doc: http://docs.openlinksw.com/virtuoso/dbadm/ <http://docs.openlinksw.com/virtuoso/dbadm/> 
>>>>>> but is it dangerous to set it to 1 and continue writing and reading virtuoso while it does the checkpoint? 
>>>>>> If dangerous, what can happen? if not, why it's not the default?
>>>>>> 
>>>>>> We have an API that calls virtuoso and it gets an Exception during the checkpoint:
>>>>>> "com.hp.hpl.jena.sparql.engine.http.QueryExceptionHTTP: File not found"
>>>>>> 
>>>>>> Best regards,
>>>>>> Balazs Varhegyi
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