Describe the problem

While a big data import migrating a huge mongo database into cockroachdb, suddenly the processed stopped importing. The reason: duplicate key value. But I do have ON CONFLICT DO NOTHING active. I got a doubt and was just able to reproduce it. The reason for this is:

We do bulk inserts to go through the import faster. But it turns out in the same batch the same key pair (a distinct key made from 3 fields) appeared at least twice. Cockroachdb does not handle this well yet. This is clearly a bug and only happens in this scenario, if the database holds a value for the duplication already, the conflict handling will work even though there are multiple entries for this key in the statement.

Expectation

The expectation I have from cockroachdb is: If in the same bulk insert statement a key conflict exists and there is an ON CONFLICT DO NOTHING, write the first value and ignore further ones. This is how they would be treated should a value exist in the database already anyways though.

To Reproduce

Create a table with some unique value (we had a primaryKey spanned over 3 columns) and execute a bulk statement. The table should not have any record yet with the same key.

INSERT INTO "table" ("key1", "key2", "key3", "randomfield") VALUES (12,12,13,"1"), (12,12,13,"2") ON CONFLICT DO NOTHING