I'm trying to perform an upsert using the Dataloader. Basically, I have records with duplicate ID numbers. This is not a mistake (but probably a source of larger data integrity issues). They are two parts of the same object and I want to keep them both.

Naturally, dataloader doesn't like this and returns the error:
Duplicate external id specified...

In setup for this object, the box do not allow duplicate values is not checked.

Any advice for me?

2 Answers 2


If Batch size of 1 via dataloader is too slow for you.

  1. Use excel to sort by Accountid
  2. Separate the Duplicate Accountids into different csvs, making sure each csv you load has only unique Accountids
  3. Load each CSV via Dataloader with batch size of any given number (2000 is max)

If you have duplicate ids but need them processed you could break this into multiple transactions, such that no two duplicate ids are processed together. For example assuming you can live with a batch size of 1 for this work, you could set Data Loaders batch size to 1.

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