4.2: cluster installation - stress test - error in edit mode

2 4.2 cluster (one indexing/authoring server and one publishing server) - 20 pages on my site (one template of each type + some basic content) - some load both in edit mode (25 simultaneous LDAP users - one hit every 5 sec =5 concurrent users) and the same in live mode on the publishing server.

On the authoring server, I got several time the following exception... so I do not know on which templates it occurs, if this is linked to the edit mode or if this is a collusion of users trying to access the same page at the same time... but I give to you the exception:

6402692 [http-8080-Processor54] INFO - Processed [/jahia/Jahia/op/edit/pid/6] user=[HAICHE] ip=[10.8.37.52] in [172ms]
newportlets.jsp>Column count for row 1 = 2
6403176 [http-8080-Processor21] INFO - Processed [/jahia/Jahia/op/edit/pid/35] user=[GGAIDON] ip=[10.8.37.52] in [16ms]
lastname dans jsp bottom: test
6403442 [http-8080-Processor57] INFO - Processed [/jahia/Jahia/op/edit/pid/36] user=[GGENTY] ip=[10.8.37.52] in [5938ms]
6403520 [http-8080-Processor53] INFO - Processed [/jahia/Jahia/op/edit/pid/18] user=[GGIORDAN] ip=[10.8.37.52] in [7125ms]
6403629 [http-8080-Processor44] ERROR - Error in PagePropertyDB.setPageProperty : ERROR: duplicate key violates unique constraint "jahia_pages_prop_pkey" -> BAILING OUT
6403629 [http-8080-Processor44] ERROR -
java.sql.SQLException: ERROR: duplicate key violates unique constraint "jahia_pages_prop_pkey"
at org.postgresql.core.v3.QueryExecutorImpl.receiveErrorResponse(QueryExecutorImpl.java:1471)
at org.postgresql.core.v3.QueryExecutorImpl.processResults(QueryExecutorImpl.java:1256)
at org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:175)
at org.postgresql.jdbc2.AbstractJdbc2Statement.execute(AbstractJdbc2Statement.java:388)
at org.postgresql.jdbc2.AbstractJdbc2Statement.executeWithFlags(AbstractJdbc2Statement.java:329)
at org.postgresql.jdbc2.AbstractJdbc2Statement.executeUpdate(AbstractJdbc2Statement.java:281)
at org.apache.commons.dbcp.DelegatingPreparedStatement.executeUpdate(DelegatingPreparedStatement.java:101)
at org.jahia.services.database.PreparedStatementWrapper.executeUpdate(PreparedStatementWrapper.java:70)
at org.jahia.services.pages.PagePropertyDB.setPageProperty(PagePropertyDB.java:108)
at org.jahia.services.pages.ContentPage.setProperty(ContentPage.java:2212)
at org.jahia.services.pages.ContentPage.incrementCounter(ContentPage.java:962)
at org.jahia.services.pages.JahiaPage.incrementCounter(JahiaPage.java:455)
at org.jahia.engines.core.Core_Engine.processCore(Core_Engine.java:160)
at org.jahia.engines.core.Core_Engine.handleActions(Core_Engine.java:109)
at org.jahia.operations.OperationManager.generatePage(OperationManager.java:330)
at org.jahia.operations.OperationManager.processPage(OperationManager.java:200)
at org.jahia.operations.OperationManager.handleOperations(OperationManager.java:179)
at org.jahia.bin.JahiaAction.execute(JahiaAction.java:50)
at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:421)
at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:226)
at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1164)
at org.jahia.bin.Jahia.process(Jahia.java:1560)
at org.jahia.bin.Jahia.service(Jahia.java:864)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:809)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:200)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:146)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:209)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:596)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:433)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:948)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:144)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:596)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:433)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:948)
at org.apache.catalina.core.StandardContext.invoke(StandardContext.java:2358)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:133)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:596)
at org.apache.catalina.valves.ErrorDispatcherValve.invoke(ErrorDispatcherValve.java:118)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:594)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:116)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:594)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:433)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:948)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:127)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:596)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:433)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:948)
at org.apache.coyote.tomcat4.CoyoteAdapter.service(CoyoteAdapter.java:152)
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:595)
6403723 [http-8080-Processor53] INFO - Processed [/jahia/Jahia/op/edit/pid/4] user=[GGALL] ip=[10.8.37.52] in [31ms]
6403910 [http-8080-Processor58] INFO - Processed [/jahia/Jahia/op/edit/pid/16] user=[GGAIGNAIRE] ip=[10.8.37.52] in [6609ms]
6404864 [http-8080-Processor26] INFO - Processed [/jahia/Jahia/op/edit/pid/31] user=[GGHIRINGHELLI] ip=[10.8.37.52] in [6907ms]
6404926 [http-8080-Processor56] INFO - Processed [/jahia/Jahia/op/edit/pid/24] user=[HMAVOUNGOU] ip=[10.8.37.52] in [5062ms]