Yesterday the SharePoint Team posted on their blog about a major issue with the latest Cumulative Update for SharePoint 2010 and recommending not to install it. If you have installed it you might experience major problems with User Profile services - contact Microsoft Support as soon as possible for help.
So what about these Cumulative Updates?
Everyone that has been in the business for some time working with products such as SharePoint and other products such as SQL Server knows that the CU's are coming every each month or quarter. These updates contains the latest hotfixes assembled into a one package to make it easier for you to patch your server product. One problem with these CU's (not the actual CU's though) is that a lot of people download them and install them as soon as they are released - Fail! This is not the intended purpose of Cumulative Updates, let me explain why:
Since the CU's contains of hotfixes, critical on-demand fixes and security fixes; some might already be available for download and some can only be reached through the Microsoft Support Services. A hotfix is intended to fix one or more specific bugs. The aim is to release a high-quality fix in an acceptable time frame - which in some cases might be a real issue. Sometimes there is not enough time to thoroughly test each hotfix for the wide diversity of environment and use-cases. One problem with the CU thing is that Microsoft also try to release them on a predictable schedule - this also means that there is not enough time to test.
If you need to install a hotfix or a CU you must (just as you do with custom code or similar) test the installation before applying it to the production servers. One problem I've seen here is the lack of a test/staging environment where you can apply these hotfixes - if you do not have these environments - do not install the fixes! Even if you have a staging environment the best tip is to wait for a Service Pack, more about these later, or take it easy and listen (read Twitter, blogs etc.) for any issues. Oh, and how about making sure that you have a backup plan!
For each and every hotfix Microsoft releases a set of Knowledge Base articles describing (almost) exactly what the hotfix is intended to fix. Before applying even the smallest hotfix - make sure that you read and understand the KB articles and also that you are experiencing the problems mentioned. If you do not experience them - there is no reason to apply the fix!
The KB articles might not be ready when the CU/hotfix is published (back to the time frame issue). So wait until it is published and then read it. But still - only apply fixes that fix a problem you are having or if the CSS tells you to install it.
Sooner or later Microsoft bundles all CU's, hotfixes and optionally some new features together into a Service Pack. These are treated differently since most often there are more time to plan and test these. Service Packs are not flawless though. Same goes for all patching, updating, upgrading etc. - TEST, TEST and TEST!
Been there, done that...
I know I shouldn't throw stones in a glass house - I've been too trigger happy sometimes finding that a CU fixes one of my problems, installed it without testing enough and finally finding out that it only caused me more trouble on another end. Nevertheless I've learned my lesson...
You can read more about the CU's in this KB article: http://support.microsoft.com/kb/953878