In this article we will discuss Lightweight Transactions(LWT) in
Cassandra which is also help to improve performance.
Sometimes insert or update operations must be unique which require a
read-before-write. The read-before-write has performance implications – Use wisely! This type of problem solved by CQL Lightweight Transactions (LWT) by using an IF clause on inserts and updates.
For Example:
Creating a keyspace:
CREATE KEYSPACE IF NOT EXIST keyspace1
WITH replication = {'class': 'SimpleStrategy',
'replication_factor' : 2};
Creating a table:
CREATE TABLE User (
U_email text,
U_password int,
U_id UUID,
PRIMARY KEY (email)
);
To read used the following CQL query.
Select *
from keyspace1.User
where U_email = ‘ashish@gmail.com’;
Output:
[0 rows]
To insert the data into table used the following CQL Query.
Insert into keyspace1.User (U_email, U_password, U_id)
values (‘ashish@gmail.com’, ‘password_A’, uuid())
if not exists;
Let's have a look.
👁 Image
Now, LWT created the row.
Select *
from keyspace1.User
where U_email = ‘ashish@gmail.com’;
Output:
[1 rows] LWT created the row
LWT on Existing Row:
Insert into keyspace1.User (U_email, U_password, U_id)
values (‘ashish@gmail.com’, ‘password_XYZ’, uuid())
if not exists;
Let's have a look,
👁 Image
Here is the output of the above CQL query.
👁 Image
Select *
from keyspace1.User
where U_email = ‘ashish@gmail.com’;
Output:
👁 Image
Lightweight Transactions(LWT) on Updating Row:
CQL query for updating an existing row and now we are applying LWT on this. CQL query for updating an existing row.
UPDATE keyspace1.User SET U_password = 'password_XYZ'
WHERE U_email = 'ashish@gmail.com'
IF U_password = 'password_A' ;
Operators can be used for UPDATE command:
=, <,, >=, != and IN
Let's have a look,
👁 Image
