12.14Why Salesforce unique External IDs are valuable

Suppose two Mule workers both simultaneously perform:

Upsert C001

Salesforce can enforce uniqueness on the External ID.

Now the race is handled by the downstream system rather than by fragile Mule-side logic.

That is much safer than:

Mule Query
↓
record not found
↓
Create

because both workers could query before either creates.