Peter,
On 18 Jun 2009, at 23:38, Peter Ansell wrote:
Hi all,
----- Original Message ----
From: Yves Raimond <[email protected]>
To: [email protected]
Sent: Thursday, 18 June, 2009 9:57:51 PM
Subject: [Virtuoso-devel] Deadlocking and slow queries
Another major issue we're running into is the deadlocking mechanism.
We have a constant flow of updates going in through SPARQL/Update.
Our
dataset is a collection of fairly small graphs (around 30 triples
each). When we do a query like the above, going through all these
graphs, we're almost sure to reach a deadlock at some point. At
almost
any point in time, there is an update going on in one of the graphs.
I have been having this issue too as I am fairly constantly running
SPARQL INSERT's on a single graph and intermittently asking the
graph for results. It would be nice to have a consistent solution
if possible even if the read-only query is postponed for a second
to allow the concurrent insert to run its course. None of the
inserts are very large (30 or so triples each), so it is a little
strange that the two queries needed to interfere with each other. I
have five indexes on the RDF_QUAD table btw if that interferes with
things. (RDF_QUAD_GPOS RDF_QUAD_OGPS RDF_QUAD_OPGS RDF_QUAD_POGS
RDF_QUAD_SPOG)
The whole database actually silently locked up at one point and
stopped INSERT's working at all when I was experimenting with
CLEAR'ing the graph while INSERT's were happening, but I restarted
it and haven't tried the same thing again so I can't say whether it
was a consistent bug. You might be able to test some concurrent
CLEAR GRAPH queries along with consistent INSERT's (every second or
so)and see if the lockup happens in a test scenario.
The inserts are some experimental statistics gathering based on
Bio2RDF queries that I thought would be cool and I want to
periodically check the progress without stopping the statistics
gathering process.
[Hugh] When perform SPARUL inserts/updaes/deletes you should use the
log_enable(2) function in you client to force the query to autocommit
and release all locks immediately as detailed at:
http://docs.openlinksw.com/virtuoso/
rdfperformancetuning.html#rdfperfsparul
http://docs.openlinksw.com/virtuoso/fn_log_enable.html
Note if you are querying directly against SPARQL endpoint you will
need to pass the the following pragma to set log_enable(2) for each
query:
define sql:log-enable 2
This resolved Yves's problem which was discussed on the "openlink-
virtuoso" IRC ...
Best Regards
Hugh Williams
OpenLink Software
Cheers,
Peter
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