Concerning the other servers in the server group, the behavior is discussed in one of the AR server guides, but I'm not sure which one (it's been a while since I read it). It probably wouldn't be too hard to find if needed.
In a nutshell, though, each of the servers in the server group periodically checks to see if the schema has been updated (or if new groups have been added, etc.), and builds a new copy of the cache from the database when they see that it has changed. If I recall correctly, the polling frequency may be able to be configured in ar.conf, and it doesn't immediately update once it notices a change. Rather, it will wait until something like two successive polling cycles have passed without additional changes occurring before rebuilding its local cache. That way, it's less likely to do an update in the middle of a set of changes. If Dev Cache Mode is turned off on the other servers in the group, and users are logged into those servers, users will continue to use the old copy of the cache until they log out and back in again. Note that this means that, depending on the frequency of changes (including adding new Remedy group or ITSM Support Groups), this can be a significant source of memory usage on the server. We have run out of memory and had the server crash in the past due to creating several new Support Groups throughout the day, and each one causing yet another copy of the cache to be held in memory for the people that logged in since the last time it was updated. This is even more of an issue if people don't log out correctly (e.g., if they're using the mid-tier and simply close their browser window without logging out), as the system will NOT log them out automatically, even though it will eventually release their write licenses. This causes old copies of the cache to be retained for longer periods than necessary. The old copies of the cache will be held in memory until everyone that was using that particular copy log out of Remedy; it will then release it, and you memory usage will drop. Like I said, that's from memory and recent experience. I do recall reading it in one of the guides in the standard documentation, so you should be able to find the specifics if you want them. Lyle From: Action Request System discussion list(ARSList) [mailto:[email protected]] On Behalf Of Tony Worthington Sent: Friday, November 20, 2009 12:28 PM To: [email protected] Subject: Re: Development Cache Mode revisited ** Be aware that (mysterious) things in ITSM7 trigger recaches -- not just definition imports or changes. I haven't quite figured out what -- but we have one or two a day -- no admin involved. They show as Remedy Application Service user. Some can be traced to group changes, which we now perform after-hours. Others are a mystery. I don't think there are db read differences when updating the cache - just the server handling of the in-memory copy. If you watch the size of the server when doing changes on vs. off you should see the differences. What happens with the cache in the other servers in the server group? I think this is dealt with in the server_cache, servgrp_board and servgrp_cache and related servgrp_* tables. No server group here so I can't say for sure. My thinking is the server watches for a signal to trigger a recache. That signal is is an API call or a change in the meta-data. Can anyone confirm how it really works? Tony Worthington | Sr. Technical Analyst | Kohl's Department Stores N56 W17000 Ridgewood Drive | Menomonee Falls, WI 53051 | office: (262) 703-7763 | e-mail: [email protected] From: Misi Mladoniczky <[email protected]> To: [email protected] Date: 11/20/2009 01:13 PM Subject: Re: Development Cache Mode revisited Sent by: "Action Request System discussion list(ARSList)" <[email protected]> ________________________________ Lyle and Tony, Thank you for the reply. In other words, there should be no impact whatsoever if you perform NO admin-changes. If you apply your changes when both users, email engine and escalations are taking it easy, it would probably be faster to use Developer Cache Mode even in production (Cache-Mode: 1). Two more questions: 1. I turned on SQL-logs to see what happened when disabling an escalation with both settings. Nothing much happened, and the server did not seem to reread much from the database repository. I had expected a bunch of SQL-selects from the repository. Maybe it just updated the memory cache without rereading the DB? 2. What happens with the cache in the other servers in the server group? Is the admin-change propagated to these in some magic way? Best Regards - Misi, RRR AB, http://rrr.se<http://rrr.se/> > I just worked through a longstanding issue that we have had in our > environment related to Dev Cache Mode. Due to extremely slow performance > when making admin changes on a 7.0 server, I had gotten into the habit of > keeping our admin server set with Dev Cache Mode turned on, which > significantly sped up migrations to production and such. However, in this > environment (7.1 p5 server), I was seeing exactly the opposite - admin > changes were very frequently timing out and migrations were painfully slow > (for example, a patch that took a few minutes to apply in dev and stage > took an hour and twenty minutes to apply in production). Thinking that it > should go faster since Dev Cache Mode was turned on, I looked everywhere I > could think of to try and isolate why it was so slow. I got BMC involved > in my search twice. This last time, the support rep forwarded this same > KB article to me and recommended that I leave Dev Cache Mode turned OFF in > order to improve performance with admin actions. I tried it, and it > worked. My migrations now go very quickly, and I haven't seen any > timeouts since. The only slowness is in the initial period where the AR > server creates a copy of the cache in memory, but that's generally fairly > quick, since it's just doing an in memory copy rather than trying to pull > it all from the database again (like I suspect it was doing on the 7.0 > server). > > In short, in our environment, we see significantly better performance > making admin changes in production with Dev Cache Mode turned off. The > support rep told me that since AR Server 7.1, their recommendation is to > keep it turned off. > > That said, if I understand it correctly, your mileage may vary depending > on what kind of activity you have going on on the server you're trying to > make changes on. As I understand it, when Dev Cache Mode is turned on, > since it doesn't make a copy of the cache for existing users, it has to > wait until user operations have ceased before it can make the change, then > it makes the change in between user operations. In our case, since this > server also runs all our back-end processes (e-mail, escalations, etc.), > and we apparently have some things going on that take a long time to > complete, the admin thread ended up having to wait a long time (more than > 10 minutes in some cases) before it could get a lock on the cache and make > the changes. This was what was causing the timeouts and slow performance > that we saw. Now, since it simply makes a relatively quick copy of the > cache for existing user operations (just system operations in our case, > but still, they're ongoing), the overall time to make the changes is > quick, because once the cache is copied, it can proceed with the changes > without having to wait for a break between user operations. > > So, if you don't have much going on on the server you're trying to make > admin changes on, it could be quicker to leave Dev Cache Mode turned on, > because then you don't have to wait for the cache to get copied (I think > it takes less than 30 seconds in our case to copy about 400MB of cache). > However, if you have lots of stuff going on (e-mail, user access, > escalations, etc.), you may see better performance with it turned off. > > I hope this helps a bit. > > Lyle > > > From: Action Request System discussion list(ARSList) _Platinum Sponsor: [email protected] ARSlist: "Where the Answers Are"_ NOTICE: This email message is for the sole use of the intended recipient(s) and may contain confidential and privileged information. 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