On Fri, Oct 24, 2008 at 7:58 PM, Adam Rybicki <[EMAIL PROTECTED]> wrote:
> Scott, > > I mis-diagnosed the issue. I just ran the same test, except I only ran one > instance of memcached. I am getting a high error rate on ticket > validations. So, it has nothing to do with memcached replication. To > investigate further, I disabled the second CAS server, and all errors are > gone. Of course that is not a viable workaround. :-) > > My guess is that the error occurs when a ticket issued by one CAS server is > being validated on another CAS server. I could not find a way to enable > debug logging in /cas/serviceValidate, but I think I have found a major > clue. It took most of the day today to hunt this down. > > With a single instance of memcached running in verbose mode you can see a > sequence of messages like this: > ------------------------------ > <11 add ST-8023-M0sU2U2ijyQ53QPYWnGm-arybicki1 1 300 2689 > >11 STORED > <7 get ST-8023-M0sU2U2ijyQ53QPYWnGm-arybicki1 > >7 sending key ST-8023-M0sU2U2ijyQ53QPYWnGm-arybicki1 > >7 END > <7 replace ST-8023-M0sU2U2ijyQ53QPYWnGm-arybicki1 1 300 2689 > >7 STORED > <7 delete ST-8023-M0sU2U2ijyQ53QPYWnGm-arybicki1 0 > >7 DELETED > ------------------------------ > This is when everything went OK. The sequence below, however, represents a > service ticket that failed to validate. That's apparently because an > attempt to read the ticket was made before it was actually stored in cache! > ------------------------------ > <11 add ST-8024-tKeeo5gYhjqoQzstAgqO-arybicki1 1 300 2689 > <7 get ST-8024-tKeeo5gYhjqoQzstAgqO-arybicki1 > >7 END > >11 STORED > ------------------------------ > There may be some code that synchronizes access to the same object from the > same client. However, it would seem that the service ticket is returned by > CAS before it's actually stored in memcached. If this service ticket is > then presented to another instance of CAS for validation, it fails to > retrieve it from memcached because the "add" operation has not completed. > > Again, I have to emphasize that this is not an unrealistic test. The > jMeter is simply following redirects at the time of the failure, as a > browser would. > We never saw that in production and we ran 500 virtual users. However, if you are experiencing it, you most likely could update the MemcacheTicketRegistry to block on the Futures. I've actually updated the code in HEAD with an option to block on Futures. :-) I have not tried it at all, since I wrote it all of 30 seconds ago. You can grab it from HEAD and try it out. The new property to enable it is "synchronizeUpdatesToRegistry" Let me know if it helps/doesn't help. -Scott > > Adam > > Scott Battaglia wrote: > > You have no need for sticky sessions. If you have two repcached servers > and you've told your CAS instance about both of them, the memcached client > essentially sees them as two memcached servers (since its not familiar with > repcached). > > The memcached client works in that it takes a hash of the key and that > determines what instance of memcached/repcached to store the item on. > repcached will then do its async replication. When you come to validate a > ticket the memcached client will again hash the key to determine what server > the item is stored on. If that server is unreachable (as determined by the > memcached client) then it will try the next likely server that would hold > the data. > > -Scott > > -Scott Battaglia > PGP Public Key Id: 0x383733AA > LinkedIn: http://www.linkedin.com/in/scottbattaglia > > > On Fri, Oct 24, 2008 at 8:21 AM, Andrew Ralph Feller, afelle1 < > [EMAIL PROTECTED]> wrote: > >> So what you are saying is that even with replication enabled, asynchronous >> replication CAS clusters should have sticky sessions on regardless? I >> realize that synchronous replication CAS cluster have no need of sticky >> sessions seeing as how it goes to all servers before the user can move on. >> >> Andrew >> >> >> On 10/23/08 9:29 PM, "Scott Battaglia" <[EMAIL PROTECTED]> wrote: >> >> It actually shouldn't matter if the async works or not. The memcache >> clients are designed to hash to a particular server and only check the >> backup servers if the primary isn't available. >> >> So you should always be validating against the original server unless its >> no longer there. >> >> -Scott >> >> -Scott Battaglia >> PGP Public Key Id: 0x383733AA >> LinkedIn: http://www.linkedin.com/in/scottbattaglia >> >> >> On Thu, Oct 23, 2008 at 9:17 PM, Adam Rybicki <[EMAIL PROTECTED]> >> wrote: >> >> >> Scott, >> >> I have run into a issue with MemCacheTicketRegistry and was wondering if >> you have any thoughts. I didn't want to create a new thread for this note. >> Anyone else with comments should feel free to reply, too. ;-) >> >> My tests have shown that when a ticket is generated on a CAS cluster >> member it may sometimes fail to validate. This is apparently because the >> memcached asynchronous replication did not manage to send the ticket replica >> in time. Fast as repcached may be, under a relatively light load, ST >> validation failed in 0.1% of the cases, or once in 1000 attempts. It would >> seem that the following tasks should be fairly complex: >> >> - Browser accesses a CAS-protected service >> - Service redirects to CAS for authentication >> - CAS validates the TGT >> - CAS issues the ST for service >> - CAS redirects the browser to service >> - Service sends the ST for validation >> >> But they are fast! My jMeter testing showed this taking 28 milliseconds >> under light load on CAS server , which is amazingly fast. Please note that >> in real life, this can be just as fast because the browser, CAS, and service >> perform these steps without the user slowing them down. CAS is indeed a >> lightweight system, and memcached does nothing to slow it down. It seems >> that in 0.1% of the cases this outperforms repcached under light load. The >> bad news is that under heavy load the failure rate increases. I've seen as >> bad as 8% failure rate. >> >> Have you or anyone else seen this? Have you had to work around this? >> >> Thanks, >> Adam >> >> Scott Battaglia wrote: >> >> >> On Tue, Oct 14, 2008 at 11:15 AM, Andrew Ralph Feller, afelle1 < >> [EMAIL PROTECTED]> wrote: >> >> >> >> >> Hey Scott, >> >> Thanks for answering some questions; really appreciate it. Just a handful >> more: >> >> >> >> 1. What happens whenever the server it intends to replicate with is >> down? >> >> >> >> >> >> It doesn't replicate :-) The client will send its request to the primary >> server and if the primary server is down it will replicate to the secondary. >> The repcache server itself will not replicate to the other server if it >> can't find it. >> >> >> >> >> >> >> 1. >> 2. >> 3. What happens whenever it comes back up? >> >> >> >> >> >> The repcache servers will sync with each other. The memcache clients will >> continue to function as they should >> >> >> >> >> >> >> 1. >> 2. >> 3. Does the newly recovered machine synchronize itself with the other >> servers? >> >> >> >> >> >> The newly recovered machine with synchronize with its paired memcache >> server. >> >> -Scott >> >> >> >> >> >> >> 1. >> 2. >> >> >> Thanks, >> Andrew >> >> >> On 10/14/08 9:56 AM, "Scott Battaglia" <[EMAIL PROTECTED] < >> http://[EMAIL PROTECTED]> > wrote: >> >> >> >> >> >> Memcache, as far as I know, uses a hash of the key to determine which >> server to write to (and then with repcache, its replicated to its pair, >> which you configure). >> >> -Scott >> >> -Scott Battaglia >> PGP Public Key Id: 0x383733AA >> LinkedIn: http://www.linkedin.com/in/scottbattaglia >> >> >> On Tue, Oct 14, 2008 at 10:38 AM, Andrew Ralph Feller, afelle1 < >> [EMAIL PROTECTED] <http://[EMAIL PROTECTED]> > wrote: >> >> >> >> >> Scott, >> >> I've looked at the sample configuration file on the JA-SIG wiki, however I >> was curious how memcached handles cluster membership for lack of a better >> word. One of the things we are getting burned on by JBoss/Jgroups is the >> frequency the cluster is being fragmented. >> >> Thanks, >> Andrew >> >> >> >> >> >> On 10/14/08 8:58 AM, "Scott Battaglia" <[EMAIL PROTECTED] < >> http://[EMAIL PROTECTED]> <http://[EMAIL PROTECTED]> > >> wrote: >> >> >> >> >> >> We've disabled the registry cleaners since memcached has explicit time >> outs (which are configurable on the registry). We've configured it by >> default with 1 gb of RAM I think, though I doubt we need that much. >> >> -Scott >> >> -Scott Battaglia >> PGP Public Key Id: 0x383733AA >> LinkedIn: http://www.linkedin.com/in/scottbattaglia >> >> >> >> >> On Mon, Oct 13, 2008 at 11:41 PM, Patrick Hennessy <[EMAIL PROTECTED] < >> http://[EMAIL PROTECTED]> <http://[EMAIL PROTECTED]> > wrote: >> >> >> >> >> >> I've been working on updating from 3.2 to 3.3 and wanted to give >> memcached a try instead of JBoss. I read Scott's message about >> performance and we've had good success here with memcached for other >> applications. It also looks like using memcached instead of JBoss will >> simplify the configuration changes for the CAS server. >> >> I do have the JBoss replication working with CAS 3.2 but pounding the >> heck out of it with JMeter will cause some not so nice stuff to happen. >> I'm using VMWare VI3 and configured an isolated switch for the >> clustering and Linux-HA traffic. I do see higher traffic levels coming >> to my cluster in the future, but I'm not sure if they'll meet the levels >> from my JMeter test. (I'm just throwing this out there because of the >> recent Best practice thread.) >> >> If I use memcached, is the ticketRegistryCleaner not needed anymore? I >> left those beans in the ticketRegistry.xml file and saw all kinds of >> errors. After taking it out it seems to load fine and appears to work, >> but I wasn't sure what the behavior is and I haven't tested it further. >> What if memcached fills up all the way? Does anyone have a general >> idea of how much memory to allocate to memcached with regards to >> concurrent logins and tickets stored? >> >> Thanks, >> >> Pat >> -- >> =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= >> >> Patrick Hennessy ([EMAIL PROTECTED] < >> http://[EMAIL PROTECTED]> <http://[EMAIL PROTECTED]> ) >> >> >> Senior Systems Specialist >> Division of Information and Educational Technology >> Delaware Technical and Community College >> =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= >> _______________________________________________ >> Yale CAS mailing list >> >> [email protected] <http://[email protected]> < >> http://[email protected]> >> >> http://tp.its.yale.edu/mailman/listinfo/cas >> >> >> >> >> >> >> ------------------------------ >> _______________________________________________ >> Yale CAS mailing list >> [email protected] <http://[email protected]> < >> http://[email protected]> >> >> http://tp.its.yale.edu/mailman/listinfo/cas >> >> >> >> >> >> >> >> -- >> Andrew R. Feller, Analyst >> Information Technology Services >> 200 Fred Frey Building >> Louisiana State University >> Baton Rouge, LA 70803 >> (225) 578-3737 (Office) >> (225) 578-6400 (Fax) >> >> >> >> _______________________________________________ >> Yale CAS mailing list >> [email protected] >> http://tp.its.yale.edu/mailman/listinfo/cas >> >> >> >> >> >> >> >> ------------------------------ >> >> _______________________________________________ >> Yale CAS mailing list >> [email protected] >> http://tp.its.yale.edu/mailman/listinfo/cas >> >> >> >> _______________________________________________ >> Yale CAS mailing list >> [email protected] >> http://tp.its.yale.edu/mailman/listinfo/cas >> >> >> >> ------------------------------ >> _______________________________________________ >> Yale CAS mailing list >> [email protected] >> http://tp.its.yale.edu/mailman/listinfo/cas >> >> >> -- >> Andrew R. Feller, Analyst >> Information Technology Services >> 200 Fred Frey Building >> Louisiana State University >> Baton Rouge, LA 70803 >> (225) 578-3737 (Office) >> (225) 578-6400 (Fax) >> >> _______________________________________________ >> Yale CAS mailing list >> [email protected] >> http://tp.its.yale.edu/mailman/listinfo/cas >> >> > ------------------------------ > > _______________________________________________ > Yale CAS mailing [EMAIL PROTECTED]://tp.its.yale.edu/mailman/listinfo/cas > > > _______________________________________________ > Yale CAS mailing list > [email protected] > http://tp.its.yale.edu/mailman/listinfo/cas > >
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