# OPC HDA aggregation mode

**URL:** <https://forum.inductiveautomation.com/t/opc-hda-aggregation-mode/33572>\
**Category:** Ignition\
**Created:** [April 1, 2020, 12:43am UTC](https://forum.inductiveautomation.com/t/opc-hda-aggregation-mode/33572 "2020-04-01T00:43:10Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![SamuelsenLarsen](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/samuelsenlarsen/32/11901_2.png) [@SamuelsenLarsen](https://forum.inductiveautomation.com/u/SamuelsenLarsen)\
**Post date:** [April 1, 2020, 12:43am UTC](https://forum.inductiveautomation.com/t/opc-hda-aggregation-mode/33572/1 "2020-04-01T00:43:10Z")

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Hi,

I have a OPC HDA interface to Factory Talk Historian SE, an OsiSoft PI database. I do have some latency when using EasyChart with pens pointing to this historical database.

After 10-20 sec, the client is reporting:  
“PI\_208DAS\_HDA (id=c6bdded7) Some of the requested aggregation modes are not available on the server. The backup mode ‘OPCHDA\_INTERPOLATIVE’ will be used.”

… and then the read is finished after 2 sec.

What aggregation mode shale i use?

If i write OPCHDA\_INTERPOLATIVE in the aggregation mode column i have an error in designer: “Invalid aggregation mode: OPCHDA\_INTERPOLATIVE on pen:”. Now I got the same message  
immediately in client, and the read is finished after 2 sec.