Storage Engine

What is a Write-Ahead Log (WAL) and Why Do Databases Use One?

A write-ahead log (WAL) is a durability mechanism where the database records every change as a sequential log entry on stable storage before it modifies the ac…

What is Checkpointing in a Database and Why is it Needed?

Checkpointing is the process of periodically flushing all dirty (modified but unwritten) data pages from memory to disk and recording a marker in the write-ahe…

Columnar Storage vs Row Storage: What is the Difference?

Row storage writes all columns of a single record contiguously on disk, making it fast to read or write an entire row at once, while columnar storage groups ea…

What is a Bloom Filter and How Do Databases Use It?

A Bloom filter is a compact, probabilistic data structure that tests whether an element is possibly in a set or definitely not in it, letting a database quickl…

What is an LSM-Tree and How Does it Handle Writes?

A Log-Structured Merge-tree (LSM-tree) is a storage engine design that turns random writes into fast sequential appends by first buffering writes in an in-memo…

What is a B-Epsilon Tree and How Does it Differ from a B-Tree?

A B-epsilon tree (Bε-tree) is a write-optimized variant of a B-tree that attaches a message buffer to each internal node, so inserts, updates, and deletes are…

What is Write Amplification and Why Does it Matter?

Write amplification is the ratio between the amount of data actually written to physical storage and the amount of data the application logically intended to w…

What is a Write-Ahead Log (WAL) and Why Do Systems Use It?

A write-ahead log is an append-only file that records every change durably before it is applied to the actual data structures on disk, so a crash can never los…

How Does a Write-Ahead Log Relate to an LSM-Tree?

A write-ahead log provides crash durability for a single write, while an LSM-tree is the broader storage engine architecture that uses that WAL alongside an in…