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TagHistorian Fails to Start

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Hello All, 

Recently I posted regarding the RabbitMQ issue we were having with our SystemLink server. This was resolved when we installed the newest version of SystemLink (SL 2021 R3). After installation of the new version, we are now facing yet another issue: TagHistorian failing to start/run. 

TagHistorian service will start when launched (intermittently) but crashes within seconds, if it launches at all. 

More information regarding this issue (NI Asked these questions too, we have a ticket in but maybe someone here has some insight): 
-Windows10 OS
-Not on a virtual machine
-We have noticed that in the log file it is stating Elixir has failed to start or unexpectedly crashed
-We have noticed also that there are multiple duplicate key errors regarding MongoDB 

"I am prepared to go anywhere, provided it be forward." - David Livingstone
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Something else we have observed, in MongoDB we are noticing that every tag has a duplicate with a differing UserID. 

"I am prepared to go anywhere, provided it be forward." - David Livingstone
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Accepted by topic author CMullinsEE

Well, we got it... 

After searching in our log files on a goose chase, it lead us to the MongoDB server (where you can login, and find all of your information that is utilized by MongoDB). In this instance of NI Tag Historian, all of those tags are passed through MongoDB. 

We were able to find that there were duplicate tags (quite a lot, actually) that had 2 differing factors: 
Tag 1 would have an SLS User null identification. 
Tag 2 (the same tag, duplicated) would have a SLS user identification that contained a unique number. 

After backing up the MongoDB information/folders we decided to use the MongoDB shell and delete all tags that contained the null identification information. 

You can find this command on the MongoDB website...

db.inventory.deleteMany ({ insert your filter here })

 Upon deleting the null addressed data, our TagHistorian started functioning immediately. 


😪 Making for two very tired Engineers. 

If you move to SL 2021 R3 you may want to keep your eyes open for this if you are utilizing a TagHistorian feature.

"I am prepared to go anywhere, provided it be forward." - David Livingstone
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I'm really glad you were able to track down the issue. It looks like there may have been something that went south during one of the database schema updates. What was the original SystemLink Server version that you initially started with before updating to 21 R3?


I guess another possibility is that the database schema update had started but perhaps you rebooted during the process and it didn't fully recover (which it should).

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