time travel with DLT

leelee3000
Databricks Employee
Databricks Employee

‎12-14-2023 06:30 AM

Needed some help with Time Travel with Delta Live tables
 
We were trying to figure out if we can go in and alter the history on this table, and what would happen to data that we mass upload?  By this we mean we have data from the past that we would like to upload, and were wondering what the Time Travel information would look like for that.  
 
Our concern is that since it already happened and potentially schema changes took place, data was updated etc how would that look within the Delta Live tables and its time travel output. #deltalivetables #DLT #timetravel
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leelee3000
Databricks Employee
Databricks Employee

‎12-14-2023 06:50 AM

I'm assuming Time Travel in Delta Lake doesn't allow you to change historical data versions?

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Louis_Frolio
Databricks Employee
Databricks Employee

‎12-14-2023 06:50 AM

Delta Live Tables leverage Delta Lake, or Delta Tables.  Delta tables, through transactions (e.g. insert, update, delete, merges, optimization) create versions of said Delta Table.  Once a version is created it cannot be altered, it is immutable.  You can always roll back (restore) to an ealier version of the Delta table, this action will create a new version of the table.  The older versions will always be present unless vacuum is run.

Hope this helps.

Louis

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