>From the documentation of D2RQ, have you read the following and enabled keep
>alive?
3.4 Keep-alive long-term connections #<http://d2rq.org/d2rq-language#keep-alive>
Some database servers like MySQL may terminate open client connections after
some interval (MySQL default is 8 hours). To keep alive long-term connections,
D2R can be configured to periodically run "noop" queries. This feature can be
enabled with the special property jdbc:keepAlive. An example is given below:
@prefix jdbc: <http://d2rq.org/terms/jdbc/> .
map:database a d2rq:Database;
# ... other database configuration ...
jdbc:keepAlive "3600"; # value in seconds
jdbc:keepAliveQuery "SELECT 1"; # (optionally to override default noop
query)
.
By default the noop query is “SELECT 1”, which may not work with some DBMS. For
this purpose, the default query may be overridden with a custom noop query.
Regards,
Srikar
On Aug 21, 2014, at 11:56 AM, Torsten Eid
<eid_tors...@lilly.com<mailto:eid_tors...@lilly.com>> wrote:
Hello,
I am faced with occasional problems when accessing D2RQ server. It seems that
the connection to the DB is lost.
The start page for the D2R projects can still be access (so tomcat showing it)
, but drilling down into “data” results in a HTTP 500.
Looks like the db connection is lost , error message is :
de.fuberlin.wiwiss.d2rq.D2RQException: No more data to read from socket
This happens to occasionally to oracle db’s using an oracle jdbc driver , and
much more frequently to a MS SQL DB connected where we use the latest jtds
driver. All D2R endpoints run under same tomcat instance. using D2RQ version
0.8 under a linux tomcat, system runs 24/7
if this problem occurs the log shows this (I renamed table names for this
post):
19:15:06 INFO Servlet :: Service URI = <sparql>
19:15:06 INFO SPARQL :: Query: SELECT ?s WHERE {?s ?p ?o} LIMIT 1
19:15:06 INFO SPARQL :: JenaException: I/O Error: Connection
reset: SELECT DISTINCT "ABC"."CDE"."FGH" FROM "
KLMOP"."Reason" (E0)
19:15:06 INFO ResponseHttp :: Error: URI = sparql : I/O Error:
Connection reset: SELECT DISTINCT "ABC"."CDE"."FGH"
FROM "LMNOP"."Reason" (E0)
19:15:06 WARN Servlet :: Internal server error
de.fuberlin.wiwiss.d2rq.D2RQException: Invalid state, the Connection object is
closed.; query was: SELECT DISTINCT "ABC"."FGH"."
ReasonId" FROM "ABC"."RFGH" (E0)
at
de.fuberlin.wiwiss.d2rq.sql.QueryExecutionIterator.close(QueryExecutionIterator.java:114)
at
de.fuberlin.wiwiss.d2rq.optimizer.iterators.RelationToBindingsD2RQIterator$StagePattern.closeIterator(RelationToBindingsD2RQIt
erator.java:203)
Any thougths / suggestions welcome. (Bouncing the tomcat is a workaround but
not a good solution.)
Thx in advance
Torsten
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