Hello,

I recently upgraded from ZCS 7.1.3 (on Ubuntu 10.04) to ZCS 8.0.5 (on Ubuntu 12.04). The upgrade went smoothly and 8.0.5 is running well now, except that some users are getting the following error fairly frequently:
2013-10-14 09:32:09,793 WARN [qtp571606922-24635:http://192.168.0.2:80/service/soap/NoOpRequest] [name=myusername@mydomain.com;mid=95;ip=192.168.1.1 0;ua=ZimbraWebClient - FF24 (Win)/8.0.5_GA_5839;] soap - handler exception
com.zimbra.cs.mailbox.MailboxLock$LockFailedExcept ion: too many waiters: 15
at com.zimbra.cs.mailbox.MailboxLock.lock(MailboxLock .java:50)
at com.zimbra.cs.mailbox.Mailbox.beginTransaction(Mai lbox.java:1489)
at com.zimbra.cs.mailbox.Mailbox.beginTransaction(Mai lbox.java:1474)
at com.zimbra.cs.mailbox.Mailbox.getMessagesByConvers ation(Mailbox.java:3848)
at com.zimbra.cs.mailbox.Mailbox.getMessagesByConvers ation(Mailbox.java:3841)
at com.zimbra.cs.service.mail.ToXML.encodeConversatio nSummary(ToXML.java:1038)
at com.zimbra.cs.service.mail.ToXML.encodeItem(ToXML. java:188)
at com.zimbra.cs.session.SoapSession.putQueuedNotific ations(SoapSession.java:1452)
at com.zimbra.cs.session.SoapSession.putNotifications (SoapSession.java:1393)
at com.zimbra.soap.SoapEngine.generateResponseHeader( SoapEngine.java:639)
at com.zimbra.soap.SoapEngine.dispatch(SoapEngine.jav a:426)
at com.zimbra.soap.SoapEngine.dispatch(SoapEngine.jav a:258)
at com.zimbra.soap.SoapServlet.doWork(SoapServlet.jav a:293)
at com.zimbra.soap.SoapServlet.doPost(SoapServlet.jav a:209)
at javax.servlet.http.HttpServlet.service(HttpServlet .java:727)
at com.zimbra.cs.servlet.ZimbraServlet.service(Zimbra Servlet.java:208)
at javax.servlet.http.HttpServlet.service(HttpServlet .java:820)
at org.eclipse.jetty.servlet.ServletHolder.handle(Ser vletHolder.java:654)
at org.eclipse.jetty.servlet.ServletHandler$CachedCha in.doFilter(ServletHandler.java:1320)
at com.zimbra.cs.servlet.RequestStringFilter.doFilter (RequestStringFilter.java:52)
at org.eclipse.jetty.servlet.ServletHandler$CachedCha in.doFilter(ServletHandler.java:1291)
at com.zimbra.cs.servlet.SetHeaderFilter.doFilter(Set HeaderFilter.java:57)
at org.eclipse.jetty.servlet.ServletHandler$CachedCha in.doFilter(ServletHandler.java:1291)
at org.eclipse.jetty.servlets.UserAgentFilter.doFilte r(UserAgentFilter.java:82)
at org.eclipse.jetty.servlets.GzipFilter.doFilter(Gzi pFilter.java:256)
at org.eclipse.jetty.servlet.ServletHandler$CachedCha in.doFilter(ServletHandler.java:1291)
at com.zimbra.cs.servlet.ETagHeaderFilter.doFilter(ET agHeaderFilter.java:45)
at org.eclipse.jetty.servlet.ServletHandler$CachedCha in.doFilter(ServletHandler.java:1291)
at com.zimbra.cs.servlet.ZimbraQoSFilter.doFilter(Zim braQoSFilter.java:114)
at org.eclipse.jetty.servlet.ServletHandler$CachedCha in.doFilter(ServletHandler.java:1291)
at org.eclipse.jetty.servlets.DoSFilter.doFilterChain (DoSFilter.java:474)
at org.eclipse.jetty.servlets.DoSFilter.doFilter(DoSF ilter.java:345)
at org.eclipse.jetty.servlets.DoSFilter.doFilter(DoSF ilter.java:316)
at org.eclipse.jetty.servlet.ServletHandler$CachedCha in.doFilter(ServletHandler.java:1291)
at org.eclipse.jetty.servlet.ServletHandler.doHandle( ServletHandler.java:443)
at org.eclipse.jetty.server.handler.ScopedHandler.han dle(ScopedHandler.java:137)
at org.eclipse.jetty.security.SecurityHandler.handle( SecurityHandler.java:556)
at org.eclipse.jetty.server.session.SessionHandler.do Handle(SessionHandler.java:227)
at org.eclipse.jetty.server.handler.ContextHandler.do Handle(ContextHandler.java:1044)
at org.eclipse.jetty.servlet.ServletHandler.doScope(S ervletHandler.java:372)
at org.eclipse.jetty.server.session.SessionHandler.do Scope(SessionHandler.java:189)
at org.eclipse.jetty.server.handler.ContextHandler.do Scope(ContextHandler.java:978)
at org.eclipse.jetty.server.handler.ScopedHandler.han dle(ScopedHandler.java:135)
at org.eclipse.jetty.server.handler.ContextHandlerCol lection.handle(ContextHandlerCollection.java:255)
at org.eclipse.jetty.server.handler.HandlerCollection .handle(HandlerCollection.java:154)
at org.eclipse.jetty.server.handler.HandlerWrapper.ha ndle(HandlerWrapper.java:116)
at org.eclipse.jetty.rewrite.handler.RewriteHandler.h andle(RewriteHandler.java:317)
at org.eclipse.jetty.server.handler.DebugHandler.hand le(DebugHandler.java:81)
at org.eclipse.jetty.server.handler.HandlerWrapper.ha ndle(HandlerWrapper.java:116)
at org.eclipse.jetty.server.Server.handle(Server.java :369)
at org.eclipse.jetty.server.AbstractHttpConnection.ha ndleRequest(AbstractHttpConnection.java:486)
at org.eclipse.jetty.server.AbstractHttpConnection.co ntent(AbstractHttpConnection.java:944)
at org.eclipse.jetty.server.AbstractHttpConnection$Re questHandler.content(AbstractHttpConnection.java:1 005)
at org.eclipse.jetty.http.HttpParser.parseNext(HttpPa rser.java:865)
at org.eclipse.jetty.http.HttpParser.parseAvailable(H ttpParser.java:240)
at org.eclipse.jetty.server.AsyncHttpConnection.handl e(AsyncHttpConnection.java:82)
at org.eclipse.jetty.io.nio.SelectChannelEndPoint.han dle(SelectChannelEndPoint.java:668)
at org.eclipse.jetty.io.nio.SelectChannelEndPoint$1.r un(SelectChannelEndPoint.java:52)
at org.eclipse.jetty.util.thread.QueuedThreadPool.run Job(QueuedThreadPool.java:608)
at org.eclipse.jetty.util.thread.QueuedThreadPool$3.r un(QueuedThreadPool.java:543)
at java.lang.Thread.run(Thread.java:724)
I have clients syncing via ActiveSync and also users have a particularly large number of calendar mounts (each user has a couple hundred calendar mounts: a folder for each organizational group and then a calendar mount in each folder for each user in said group). I have already adjusted the DoSFilter parameters as outlined here:
zmprov mcf zimbraHttpDosFilterMaxRequestsPerSec 100
zmprov mcf zimbraHttpDosFilterDelayMillis 20
zmmailboxdctl restart
Any ideas on what is causing this locking error, and how to resolve it?

Thanks,

Andrew