Memcache errors break the GAE-internal session handling. Our application is almost unusable now. Help, please?

[Per]

Memcache errors are frequently breaking the sessions-persistence, as there doesn't seem to be any try-catch in the GAE session handling. This results in tons of 500 errors for our end users.  This seems like fundamental flaw in the framework to me.

Uncaught exception from servlet
com.google.appengine.api.memcache.MemcacheServiceException: Memcache put: Error setting single item (_ahsvuHmc0fDcNMbpwqBsbrJ4Q)
	at com.google.appengine.api.memcache.AsyncMemcacheServiceImpl$7.transform(AsyncMemcacheServiceImpl.java:426)
	at com.google.appengine.api.memcache.AsyncMemcacheServiceImpl$7.transform(AsyncMemcacheServiceImpl.java:418)
	at com.google.appengine.api.memcache.MemcacheServiceApiHelper$RpcResponseHandler.convertResponse(MemcacheServiceApiHelper.java:60)
	at com.google.appengine.api.memcache.MemcacheServiceApiHelper$1.wrap(MemcacheServiceApiHelper.java:112)
	at com.google.appengine.api.memcache.MemcacheServiceApiHelper$1.wrap(MemcacheServiceApiHelper.java:105)
	at com.google.appengine.api.utils.FutureWrapper.wrapAndCache(FutureWrapper.java:57)
	at com.google.appengine.api.utils.FutureWrapper.get(FutureWrapper.java:98)
	at com.google.appengine.api.utils.FutureWrapper.get(FutureWrapper.java:90)
	at com.google.appengine.api.memcache.MemcacheServiceImpl.quietGet(MemcacheServiceImpl.java:28)
	at com.google.appengine.api.memcache.MemcacheServiceImpl.put(MemcacheServiceImpl.java:81)
	at com.google.apphosting.runtime.jetty.MemcacheSessionStore.saveSession(MemcacheSessionStore.java:39)
	at com.google.apphosting.runtime.jetty.SessionManager$AppEngineSession.save(SessionManager.java:164)
	at com.google.apphosting.runtime.jetty.SaveSessionFilter.doFilter(SaveSessionFilter.java:41)
	at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
	at com.google.apphosting.utils.servlet.TransactionCleanupFilter.doFilter(TransactionCleanupFilter.java:43)
	at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
	at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:388)
	at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
	at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)
	at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:765)
	at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:418)
	at com.google.apphosting.runtime.jetty.AppVersionHandlerMap.handle(AppVersionHandlerMap.java:249)
	at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
	at org.mortbay.jetty.Server.handle(Server.java:326)
	at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
	at org.mortbay.jetty.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:923)
	at com.google.apphosting.runtime.jetty.RpcRequestParser.parseAvailable(RpcRequestParser.java:76)
	at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
	at com.google.apphosting.runtime.jetty.JettyServletEngineAdapter.serviceRequest(JettyServletEngineAdapter.java:135)
	at com.google.apphosting.runtime.JavaRuntime$RequestRunnable.run(JavaRuntime.java:477)
	at com.google.tracing.TraceContext$TraceContextRunnable.runInContext(TraceContext.java:449)
	at com.google.tracing.TraceContext$TraceContextRunnable$1.run(TraceContext.java:455)
	at com.google.tracing.TraceContext.runInContext(TraceContext.java:695)
	at com.google.tracing.TraceContext$AbstractTraceContextCallback.runInInheritedContextNoUnref(TraceContext.java:333)
	at com.google.tracing.TraceContext$AbstractTraceContextCallback.runInInheritedContext(TraceContext.java:325)
	at com.google.tracing.TraceContext$TraceContextRunnable.run(TraceContext.java:453)
	at com.google.apphosting.runtime.ThreadGroupPool$PoolEntry.run(ThreadGroupPool.java:251)
	at java.lang.Thread.run(Thread.java:679)


No matter what causes the Memcache error, the exception should get caught by the framework. Or there should be a way to catch it from the application side. I've tried unsuccessfully to apply the LogAndContinue-Errorhandler. 
Is there some way to disable memcache for session-handling maybe? Or is it possible to copy select GAE source code into your own application, applying your own error-handler some way? I'd do anything to make our application work again.

I've raised a Production Issue, I've reported this in the forum. And other suggestions? I'd go premium if I had some kind of reassurance that it wouldn't simply add insult to injury.


Application ID is small-improvements.

Kind regards,
Per

[Takashi Matsuo]

Hi Per,

There is also an issue on our issue tracker:

http://code.google.com/p/googleappengine/issues/detail?id=6463

You might want to start it, and we'll likely follow up there.

Yes, it seems a real issue to me as well. I've just started an internal discussion about it.

-- Takashi

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