[Mulgara-general] Can't connect to remote Mulgara repository using ConnectionFactory

David Legg david.legg at searchevent.co.uk
Thu Nov 20 22:14:51 UTC 2008

Thanks Paul + Alex,

>> So RMI can't connect to it at all, huh? What about HTTP? On the
>> WIndows box, try to retrieve:
>> http://SearchMaster:8080/sparql/?query=select+%24subject+%24predicate+%24object+from+%3Crmi%3A%2F%2FSearchMaster%2Fserver1%23sampledata%3E+where+%7B%24subject+%24predicate+%24object%7D

That works!  I get an XML file downloaded containing the results.

>> While typing this, it occurred to me to ask about your DNS. Is
>> SearchMaster resolving to for you?

On optimus (the Linux server) SearchMaster (the Windows client) resolves 
to using nslookup but if I type 'ping SearchMaster' it 
correctly uses

>>  Try changing your
>> graph name to:
>> rmi://
>> You can also try the URL with addresses instead of host names:

This doesn't bomb out but it does return error code 500 and Jetty 
announces that the query failed.

> This reminds me of another issue I've experienced in the past.  RMI connections
> with a Mulgara server tend not to work unless the hostname on the server is
> properly set (can be easily verified using the Linux 'hostname' command).  The
> hostname needs to be a real hostname (not "localhost") which resolves to the
> external interface (not the loopback address).  Otherwise RMI connections from
> remote machines won't work; I'm not sure if this is a problem with the
> canonicalization of server names that Mulgara does, or is deeper in Java RMI.

Running 'hostname' on the Linux server correctly returns 'optimus'.  I 
had an issue a while ago with optimus not seeing the windows machines on 
the network because of the lack of a DNS but the solution was to run 
winbind which makes use of netbios calls to find their names.  I suppose 
something in RMI might assume there is a DNS service?

Ho hum, this is a real pain.  I was hoping to spend the last two days 
writing a Fresnel library to run natively over the connection to a 
remote Mulgara store.


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