'Optimizing unique_together in Django Models

I have a model containing an FK and a CharField, and this pair should be unique:

class Map(models.Model):
    uuid = models.UUIDField(unique=True, default=uuid4, editable=False, db_index=True)
    user = models.ForeignKey(User, related_name="uploaded_map", on_delete=models.CASCADE)
    workspace = models.ForeignKey(Workspace, on_delete=models.CASCADE)
    c_layer = models.CharField(max_length=40, blank=False)

    class Meta:
        unique_together = ["workspace", "c_layer"]

The project uses PostgreSQL, and I am a bit worried that this constraint will create heavy indexes because of the 40 chars limit for c_layer, but I'm not sure this is really something that will impact performance.

Would index a sha1 hash version of this field be less heavy for the DB?

pythondjangopostgresql


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