# Review No. 1

This page contains miscellaneous concepts briefly explained.

# What is the meaning of "Clean Code" ?

"Clean Code" signify a code which is easy to

• read
• maintain (fix bugs, add new functionalities with ease)
• test

Here we need to consider:

• Single Responsibility Principle
• meaningful names
• comments are not a substitute for Clean Code
• error handling
• no code duplication
• proper modularity
• keep the code simple
• good observability
• use code analysis tools like SonarQube or CodeClimate

# Shared vs Exclusive lock

• A shared (S) lock permits the transaction that holds the lock to read a row.
• An exclusive (X) lock permits the transaction that holds the lock to update or delete a row.

# Pessimistic vs Optimistic Locking

• Pessimistic Locking (when we READ/WRITE to a database) - a conflict is likely to happen and thus locks data before it is read or modified.
• Optimistic Locking (when we WRITE rarely to a database) - a conflict is NOT likely to happen and thus the data is not locked. However, a "version" column (which is incremented on each UPDATE or DELETE) and the 2nd parallel operation on the same row will not be done.