postgresql执行一个查询时报了如下一个错误

org.postgresql.util.PSQLException: An I/O error occured while sending to the backend.

at org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:281)

at org.postgresql.jdbc2.AbstractJdbc2Statement.execute(AbstractJdbc2Statement.java:555)

at org.postgresql.jdbc2.AbstractJdbc2Statement.executeWithFlags(AbstractJdbc2Statement.java:403)

at org.postgresql.jdbc2.AbstractJdbc2Statement.executeUpdate(AbstractJdbc2Statement.java:331)

at com.spy2k3.core.business.processor.ProcessorImpl.executeUpdate(ProcessorImpl.java:237)

at com.spy2k3.core.business.object.BusinessObject.executeUpdate(BusinessObject.java:54)

at com.spy2k3.core.business.object.LoginObject.deleteSession(LoginObject.java:127)

at com.spy2k3.core.business.processor.LoginProcessor.userValidation(LoginProcessor.java:79)

at com.spy2k3.core.business.processor.LoginProcessor.execute(LoginProcessor.java:30)

at com.spy2k3.core.business.processor.ProcessorImpl.process(ProcessorImpl.java:73)

at com.spy2k3.core.handler.request.RequestHandler.doService(RequestHandler.java:90)

at com.spy2k3.core.handler.AbstractHandler.doPost(AbstractHandler.java:25)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:709)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:802)

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:237)

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:157)

at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:214)

at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104)

at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520)

at org.apache.catalina.core.StandardContextValve.invokeInternal(StandardContextValve.java:198)

at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:152)

at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104)

at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520)

at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:137)

at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104)

at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:118)

at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:102)

at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520)

at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)

at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104)

at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520)

at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:929)

at org.apache.coyote.tomcat5.CoyoteAdapter.service(CoyoteAdapter.java:160)

at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:799)

at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.processConnection(Http11Protocol.java:705)

at org.apache.tomcat.util.net.TcpWorkerThread.runIt(PoolTcpEndpoint.java:577)

at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:683)

at java.lang.Thread.run(Thread.java:662)

Caused by: java.net.SocketException: Socket closed

at java.net.SocketInputStream.socketRead0(Native Method)

at java.net.SocketInputStream.read(SocketInputStream.java:129)

at org.postgresql.core.VisibleBufferedInputStream.readMore(VisibleBufferedInputStream.java:143)

at org.postgresql.core.VisibleBufferedInputStream.ensureBytes(VisibleBufferedInputStream.java:112)

at org.postgresql.core.VisibleBufferedInputStream.read(VisibleBufferedInputStream.java:71)

at org.postgresql.core.PGStream.ReceiveChar(PGStream.java:269)

at org.postgresql.core.v3.QueryExecutorImpl.processResults(QueryExecutorImpl.java:1700)

at org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:255)

这是为什么，如何解决这个问题？