Troubleshooting Over Runs / Overruns

Overview: Overruns increment when you have tags that can't collect as fast as you ask them to, but depending on which type of collector is incrementing overruns, could be a different issue.

Calc Collector: Likely due to bad code in the calculation.

OPC: Can be because of a read group that includes tags inside the group that are not defined or have the wrong address. 

Migrations: Perhaps some tags that were kept around because they had history associated with them, but they actually went out of commission long ago, and in this case, they may have set them to disabled. Disabling them allows you to read the old data while excluding them from a read group.

More about read groups: The OPC collector groups tags based on poll frequency. So if you have 10,000 tags set to 1 second poll rate, you only have 1 group of 10,000 tags. If any one of those tags is not found in the OPC Server, depending on the OPC Server and how it resolves the source address, it could slow down the whole group. So disabling bad tags can reduce or eliminate overruns.

Finding the bad tags:

• Use the excel addin to have it fetch the current "timestamp, value, and quality" of every tag. Then scroll down to fine the bad quality tags.

• Inside the Historian Admin, rightclick on and select “last 10 values”. This will display values and quality for the tag. This method is simpler but cant be applied en masse.