Understanding Write Operations in HBase: Ensuring Durability and Consistency
Learn how HBase handles write operations, ensuring data durability and consistency through its write-ahead log (WAL) and MemStore. Explore the steps involved in writing data to HBase and how it leverages these components for efficient and reliable data management.
Write Operations in HBase
Writing data to HBase involves several steps to ensure data durability and consistency. Unlike traditional databases that directly write to the main storage, HBase uses a combination of in-memory storage and a write-ahead log for efficient and reliable data handling. This section will explore how this works.
The Write-Ahead Log (WAL) and MemStore
When you perform a write operation in HBase, the data is written to two places in parallel:
- Write-Ahead Log (WAL) or HLog: A persistent log file that stores all write operations before they are applied to the main storage. This ensures that the write operation is recorded even if the database crashes.
- MemStore: An in-memory buffer that stores data temporarily before it is written to disk. This provides faster write performance but means the data is not persistent unless written to disk. The MemStore is an in-memory store that holds the data until it is flushed to disk.
Both WAL and MemStore must successfully complete a write operation for it to be considered confirmed. Clients don't directly interact with the underlying storage files (HFiles) during write operations; instead, writes go to WAL and MemStore, ensuring data durability and consistency even during system failures.