Thursday, 28 June 2012

Difference between Full load & Incremental load

In most OBIA projects we create both incremental and full load mappings for each tables in DWH target.Below you can find the difference bw both.

Full Load is the entire data dump load taking place the very first time.In this we give the last extract date as empty so that all the data gets loaded

Incremental - Where delta or difference between target and source data is dumped at regular intervals.Here we give the last extract date such that only records after this date are loaded.

  • Full load: $$Last_Extract_Date = either leave it blank or give some old date so that all the records are loaded
  • Incremental load:$$Last_Extract_Date = The date from which you need the data (to get latest record).

Why Incremental?
  1. Speed. Opting to do a full load on larger datasets will take a great amount of time and other server resources. Ideally all the data loads are performed overnight with the expectation of completing them before users can see the data the next day. The overnight window may not be enough time for the full load to complete.
  2. Preserving history. When dealing with a OLTP source that is not designed to keep history, a full load will remove history from the destination as well, since full load will remove all the records first, remember! So a full load will not allow you to preserve history in the data warehouse.
Full Load vs. Incremental Load:

Full Load
Incremental Load
Truncates all rows and loads from scratch.
New records and updated ones are loaded
Requires more time.
Requires less time.
Can easily be guaranteed
Difficult. ETL must check for new/updated rows.
Can be lost.

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