What level of transaction isolation do you apply in your projects?

In my projects, I most often used the transaction isolation levels Read Committed and Repeatable Read.

• Read Committed prevents reading "dirty" data, meaning data that has been modified but the transaction has not yet been completed. This is the standard level for many DBMSs and provides a balance between performance and integrity.

• Repeatable Read guarantees that data read within a transaction will not change until the transaction completes, preventing non-repeatable reads but allowing phantom reads.

In some cases, when maximum consistency is required, I used the Serializable level, which provides full transaction isolation but reduces concurrency and performance.

Example in SQLAlchemy (Python):

from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker

engine = create_engine('postgresql://user:pass@localhost/db')
Session = sessionmaker(bind=engine)
session = Session()
session.connection().execution_options(isolation_level="REPEATABLE READ")

# then work with the transaction