What is the purpose of the Write-Ahead Log in HBase?

The Write-Ahead Log (WAL) in HBase is a technology used to ensure data durability and consistency. When a client writes data to HBase, the data is first written to the WAL and then to the MemStore in memory. This ensures that even in the event of a system failure or unexpected termination, the data can be recovered from the WAL to maintain data integrity and consistency. When the HBase server starts up, it first recovers data from the WAL and then from the MemStore to guarantee data consistency. Therefore, the WAL plays a crucial role in HBase, ensuring data safety and reliability.