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Re: Strange JDBC problem

From: Mark Lewis <mark(dot)lewis(at)mir3(dot)com>
To: Trygve Hardersen <trygve(dot)hardersen(at)no(dot)scala(dot)com>
Cc: pgsql-jdbc(at)postgresql(dot)org
Subject: Re: Strange JDBC problem
Date: 2006-09-01 14:54:06
Message-ID: 1157122446.9657.619.camel@archimedes (view raw or flat)
Thread:
Lists: pgsql-jdbc
Wow, that sounds weird.  

We once had an application bug with a web-app where Tomcat would give a
500 error sometimes when accessed by IE, but would work fine with other
browsers.  We used a packet sniffer and verified that the requests were
pretty much identical.

It turned out that the application had multiple frames, and IE requested
the different frames with a slightly different timing than Firefox or
Opera, and that slight timing difference exposed a race condition in a
library we were using (Struts).

Perhaps your app has a similar race condition somewhere.  You should be
able to check by putting in some kind of manual synchronization so you
only deal with one request at a time, and see if the problem goes away.
It's kind of a stretch, but it would explain why the problem only
happens on localhost with IE.

-- Mark


On Fri, 2006-09-01 at 15:40 +0200, Trygve Hardersen wrote:
> Hi
> I'm experiencing a strange problem with the PostgreSQL JDBC driver on a
> project I'm working on. Our setup is like this:
> 
> JRE 1.5
> Apache Tomcat 5.5.17
> Hibernate 3.1
> C3P0 0.9.0
> PostgreSQL 8.1-407.jdbc3
> PostgreSQL 8.1.4
> 
> We exclusively use the JDBC connections through Hibernate, which again
> uses the C3P0 connection pool. Normally this setup works fine, but on
> Win2K SP4, we are experiencing strange problems. 
> 
> Randomly we get "java.net.SocketException: Connection reset". The error
> occurs in different parts of the application, but more frequently some
> places, and mysteriously much more frequent when using Internet Explorer
> 6 (IE) on the same host as the web and DB server (localhost) than when
> using Firefox (FF). In fact to begin with we thought the error only
> occurred with IE, but we've also seen it happen with FF and Opera
> sometimes, but very rarely.
> 
> There is nothing in our architecture that links the browser to the JDBC
> connection, so I cannot explain why the error almost exclusively occurs
> with IE. Even more strangely in not able to reproduce the error when
> debugging the JDBC driver (by setting loglevel=2 on the connection URL),
> nor when running against a DB on a different server, or when running
> Tomcat on a different server using the DB on the affected server. The
> application also supports MySQL and we're not seeing this error there.
> We've also not seen the error Windows XP.
> 
> Here is the stack trace from the "Connection reset" exception. For the
> sake of readability I removed some parts which I think is of no
> significance:
> 
> 01-09-2006 07:50:02,071  WARN JDBCExceptionReporter: SQL Error: 0,
> SQLState: 08006
> 01-09-2006 07:50:02,071 ERROR JDBCExceptionReporter: An I/O error
> occured while sending to the backend.
> 01-09-2006 07:50:02,081 ERROR [jsp]: Servlet.service() for servlet jsp
> threw exception
> org.hibernate.exception.JDBCConnectionException: could not initialize a
> collection: [mypackage.pojo.modules.department.Department.children#827]
> 
> ... Removed
> 
> Caused by: org.postgresql.util.PSQLException: An I/O error occured while
> sending to the backend.
>         at
> org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:
> 214)
>         at
> org.postgresql.jdbc2.AbstractJdbc2Statement.execute(AbstractJdbc2Stateme
> nt.java:452)
>         at
> org.postgresql.jdbc2.AbstractJdbc2Statement.executeWithFlags(AbstractJdb
> c2Statement.java:354)
>         at
> org.postgresql.jdbc2.AbstractJdbc2Statement.executeQuery(AbstractJdbc2St
> atement.java:258)
>         at
> com.mchange.v2.c3p0.impl.NewProxyPreparedStatement.executeQuery(NewProxy
> PreparedStatement.java:76)
>         at
> org.hibernate.jdbc.AbstractBatcher.getResultSet(AbstractBatcher.java:139
> )
>         at org.hibernate.loader.Loader.getResultSet(Loader.java:1669)
>         at org.hibernate.loader.Loader.doQuery(Loader.java:662)
>         at
> org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loade
> r.java:224)
>         at org.hibernate.loader.Loader.loadCollection(Loader.java:1919)
>         ... 89 more
> Caused by: java.net.SocketException: Connection reset
>         at java.net.SocketInputStream.read(SocketInputStream.java:168)
>         at
> java.io.BufferedInputStream.fill(BufferedInputStream.java:218)
>         at
> java.io.BufferedInputStream.read(BufferedInputStream.java:235)
>         at org.postgresql.core.PGStream.ReceiveChar(PGStream.java:256)
>         at
> org.postgresql.core.v3.QueryExecutorImpl.processResults(QueryExecutorImp
> l.java:1163)
>         at
> org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:
> 188)
>         ... 98 more
> 
> Does this make sense to any of you? It doesn't to me, but the error is
> consistent, and I've tested this a lot. Any help or suggestions are much
> appreciated.
> 
> Regards
> 
> Trygve Hardersen
> Senior Software Engineer 
> Scala Nordic
> 
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