Why is Mac Calendar non-functional in Yosemite?

Question

I installed Yosemite onto my 27" iMac (2009, intel chips, 1gb hard drive, 4 gb RAM) and all **** broke loose. Nothing worked for four days, all anything would do is to freeze up for five minutes to an hour at a time or until I used force quit to get out of there: Calendar, iPhoto, Preview, all native and third party programs. After almost a week of not being able to work, I did a re-install, which is a time consuming process. Since then, most things are working, third party software seems to work, albeit slowly and periodically spinning for minutes on end before settling down. iPhoto seems to be working again, likewise Preview, (I haven't worked my way through everything, I admit. I realize that RAM might be part of the problem (thanks for not telling us that you need 8GB to run the **** OSX) but even with no other programs running, here is what happens with Calendar: It launches. It opens every calendar, several in duplicated form (BIrthdays and US Holidays), it freezes. It acts like it's unfrozen. I click on a calendar that I don't want to view. It freezes. After a while it stops spinning and unchecks. The calendar is still visible. Repeat this for a half dozen background calendars, each time it freezes and after a few minutes it unchecks the box, but the calendar is still visible. I click on an event, it freezes for a while, then everytime I move the cursor onto the calendar it starts spinning again. After numerous attempts, I open the info box for a calendar item, it freezes, five or ten minutes later I look at it again and it seems to be okay, then when I move the cursor over the calendar, it closes the event window ande starts spinning again. I notice that all the duplicates are there and all the calendars I closed that never really closed are now checked as being visible again. After many, many attempts and freezes, at some point a few hours into the process, it lets me type a calendar item and save it (taking maybe 20 minutes through the freezing process). I quit and restart over and again, hoping that will solve the issue. Then after two days of this, I open up the calendar, all the calendars are checked again and my recent postings are missing, edits have been undone, everything is freezing and spinning, duplicates still show, etc., etc. Then I go to icloud and make some changes there. The next time Calendar locks up, I force it to quit, reopen, everything is back to being checked, duplicated, etc., but the item I posted is now on the iMac calendar, so it did sync, but again I can't work on anything because it just goes into spin mode. Almost a week into this (I did the install last Friday, today is Wednesday and I worked on it part of the weekend) I would like to stop using mac Calendar, but what calendar should I use and how do I synchronize it all and I am heavily invested in this program since it has been my main way of tracking my schedule for many years now and my business relies on it. There is no option to reinstall calendar. There are no threads discussing this problem. I have lost almost a week of income because I've spent all my office time every day since the initial install trying to get my computer functional. I am warning everyone I know to NOT upgrade to Yosemite as it is a piece of crap. Can anyone help me figure this out before I start a Facebook page "Mac Calendar is a piece of ****?" I like the program quite a bit all the way through Mavericks but now it only works via iCloud and may or may not be deleting my schedule as I go along. Any ideas? Should I just buy a different calendar program (I need to have this on my computer I can't rely on online programs due to privacy issues.) The desktop version is a clutter of duplicates and calendars that it says are hidden, and I go back to iCloud, which won't let me copy and paste or anything and I don't like that interface but at least it (seems to) syncs with my mac but not always with my iphone, Thanks. I am really hating this experience. 

Answer 1

Back up all data. If you have iCloud calendars, archive them by following the instructions on this page under the heading "Downloading a calendar from iCloud.com." All you need is a web browser, not the Calendar application. Do the same with any other network calendars you have, if possible.
Before taking each of these steps, quit (force quit if necessary) the application. After taking the step, relaunch and test. When the problem is resolved (or when you complete Step 3 without resolving it), stop and close the Library folder.  
Step 1
Hold down the option key and select
          Go ▹ Library
from the Finder menu bar. From the folder that opens, move these items (some may not exist) to the Trash, leaving the Library folder open:
          Calendars/Calendar Cache
          Calendars/Calendar Cache-shm
          Calendars/Calendar Cache-wal
Step 2
Move these files from the Library folder to the Desktop (again, some may not exist):
          Containers/com.apple.CalendarAgent (and any others with a name beginning in "com.apple.Calendar")
          Containers/com.apple.iCal (and any others with a name beginning in "com.apple.iCal")
          Preferences/com.apple.CalendarAgent.plist
          Preferences/com.apple.iCal.plist
If the problem is resolved, you may be able to put back some of the items you moved in this step, relaunching and testing after each one. Eventually you may find the one that caused the problem; delete it. Recreate your settings as necessary.
If the problem still isn't solved, put back each of the items you moved in this step, overwriting the one that may have been created in its place. You don't have to put back the files you moved in Step 1.
Step 3
Move this folder to the Desktop:
          Calendars
Note: you're not moving the Calendars application; you're moving a folder named "Calendars". If there's no change, put the folder back where it was.
If the problem is resolved after you move the Calendars folder, the event database is corrupt. You have these choices:
          Restore the folder from a Time Machine snapshot or other backup that predates the corruption.
          Use a third-party application such as Calendar Cleaner to try to repair the database.
For network calendar accounts, such as iCloud, all you should need to do is re-enter them in the preferences. For subscribed calendars, you only need to re-subscribe.