I've got three main data extensions. I have a query that segments subscribers and puts them into a separate data extension which is designated as the entry source for the journey. The journey has decision splits that point to the source data extension(s).

Here's my question - what are the impacts in terms of journey behavior if these three data extensions are overwritten on a daily basis (the overwrite will contain the same data and any additional records that might have been added). By the way, the alternative is to do an add/update on these three data extensions to update the data, and if that's the route I need to take, that's fine.

My initial thoughts are around "_CustomObjectKey" and how that affects journey behavior because the new data in these overwritten data extensions will all have new _CustomObjectKey(s). Does this matter? High water mark issues? Thoughts here?


Once a contact has entered a journey, they're in the journey and they don't need to be in the Data Extension any longer. The entry into the data extension is the event that triggers the journey. As long as you have accounted for what will happen if duplicate contacts are added to the Data Extension there should be no problem with overwriting.

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  • Thanks @Matthew. So, to confirm, if I'm making decisions in the journey that depend on data extensions (that are overwritten) outside of the journey, that shouldn't be an issue? – Mike Marks Oct 12 '18 at 20:37
  • It should be treated as Journey Data, which is post-in-time data. It should be safe to delete since that data is attached to that entrant and follows it through the journey. – Matthew Wash Oct 12 '18 at 20:43
  • Ah okay - so if my use case requires a constant, up to date version of the data at all times within the journey, I need to use Contact Data (rather than Journey Data). In that case, my guess is that overwriting might be an issue? We need to make decisions within the lifecycle of the journey that depends on the most recent, up to date values of certain fields in data extensions. – Mike Marks Oct 12 '18 at 21:01
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    Yep then in that case you might want to use contact data and separate that from your journey data. – Matthew Wash Oct 13 '18 at 0:15

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