ExecuteQuery gets stuck forever, sporadically

Question

I have a table t with around 160K records. I need to pull out all the rows an pack them in files each files with a maximum of 50K records.
The following code is called (standard pagination) with page size = 10000. That means, this code needed to be called 16 times to archive whole table into files.
query = "select  from (select t_name, row_number() over (order by t_timestamp asc) rn from t where t_id = ? and t_timestamp between ? and ?) where rn between ? and ?";               try{ conn = DriverManager.getConnection(url, user, pass); pstmt = conn.prepareStatement(query); pstmt.setFetchSize(10000); pstmt.setLong(1, t_id); pstmt.setDate(2, fromDate); pstmt.setDate(3, todate); pstmt.setLong(4, startIdx); pstmt.setLong(5, endIdx); rs = pstmt.executeQuery(); while(rs.next()){ /**get the rows and pack in ovo object*/ lst.add(ovo); } }catch{                             /*catch code*/                 }finally{   /* Clean up the resources */ try{ if(pstmt!=null) { pstmt.close(); } if (rs != null) { rs.close(); } if(conn!=null) { conn.close(); } }catch(Exception e){ /*catch code*/ } }
This code is a part of a stand-alone application. The query is pretty fast.
The problem is, the thread hangs at
pstmt = conn.prepareStatement(query);
without any error.
And this happens sporadically (some of the 16 calls fail). There is no hanging query when we see from DB side. Looks like the thread has gone in idle state. No garbage collection trace is printed.
This process fails with (connection timeout)
at oracle.jdbc.driver.SQLStateMapping.newSQLException(SQLStateMapping.java:74)
I considered following possibilities and added fix for that none worked:
1. There might be resource crunch. So, made sure preparedStatement and resultset are closed explicitly as well.
2. tested with setQueryTimeout.
3. added System.gc() before each call.
4. using pooled and non-pooled connections
Not sure what's wrong.
- Nishant

Answer 1

Tolls wrote:
I wouldn't expect high memory usage, but I would expect something along the lines of a connection timeout...maybe.
Still, rereading your OP I would also expect it to hang at the getConnection() rather than the following executeUpdate(), so it's possibly not resource leaking.
Have you tried over at OTN? [Found this post from a couple of months back.|http://forums.oracle.com/forums/thread.jspa?threadID=922664&tstart=0]
Thanks for the link.
The weirdest thing is, If I do something like this
                        pstmt.setQueryTimeout(30);
                        System.out.println("Before");
               rs = pstmt.executeQuery();
               System.out.println("After");The iteration which the code fails in, three things happen:
1. "Before" gets printed but not "After".
2. No timeout happens after 30 seconds. In fact, the timeout takes place after 90 minutes. (may be the default connection timeout)
3. there is no active query when seen from DBA tool.
I am wondering if some particular resource gets unavailable like socket or something, not sure though. Neither the error indicates that.
- Nishant