CQL performance inserting multiple cluster keys under same partition key

[Jaydeep Chovatia]

Hi,

I have question on inserting multiple cluster keys under same partition
key.

Ex:

CREATE TABLE Employee (
  deptId int,
  empId int,
  name   varchar,
  address varchar,
  salary int,
  PRIMARY KEY(deptId, empId)
);

BEGIN *UNLOGGED *BATCH
  INSERT INTO Employee (deptId, empId, name, address, salary) VALUES (1,
10, 'testNameA', 'testAddressA', 20000);
  INSERT INTO Employee (deptId, empId, name, address, salary) VALUES (1,
20, 'testNameB', 'testAddressB', 30000);
APPLY BATCH;

Here we are inserting two cluster keys (10 and 20) under same partition key
(1).
Q1) Is this batch transaction atomic and isolated? If yes then is there any
performance overhead with this syntax?
Q2) Is this CQL syntax can be considered equivalent of Thrift
"batch_mutate"?

-jaydeep