One of our client awarded us the contract of CIVICRM data migration. We were very excited that this was the first time we were doing such a big data migration (250K Contacts and related contribution data) in CIVICRM.

We started Data migration When importing data for our client we encounter with a "error already exists db error". It took little to find the reason for the same. Initially we thought that it could be data problem may the size of the data as we were importing 22K contact in single import. We ruled out php error like script execution time exceeds the limit or memory limit.

Finally we found that the problem was due to import of external identifier. in our case it was not unique. The data we received from our client had Organization_name (employer) and individual in one file. We imported organization first and try to import individual with the same external identifier and got the error.

We added another external identifier and imported the data.

So be aware that the EXTERNAL IDENTIFIER in CIVICRM should be unique for all contacts. You can reproduce the error even by create to contact record using same External Id. 

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