Disk IO

What Are Database Compression Techniques and Why Do They Matter?

Database compression techniques shrink the physical size of stored data by removing redundancy — through methods like dictionary encoding, run-length encoding,…

What is a B-Tree?

A B-tree is a self-balancing, multi-way search tree where each node can hold multiple keys and multiple children, keeping the tree shallow so search, insert, a…

What is a B+ Tree and Why Do Databases Use It?

A B+ tree is a self-balancing, multi-way search tree where all actual data (or record pointers) lives only in the leaf nodes, internal nodes hold only routing…

What is External Sorting?

External sorting is a family of algorithms for sorting data too large to fit in main memory, most commonly external merge sort: split the data into memory-size…

What is the C-SCAN Disk Scheduling Algorithm?

C-SCAN (Circular SCAN) services disk requests by sweeping the head in one direction only to the end of the disk, then jumping immediately back to the starting…

What is the LOOK Disk Scheduling Algorithm?

LOOK is a disk scheduling algorithm that moves the head in one direction servicing requests, but reverses as soon as there are no more requests in that directi…

What is Spooling in Operating Systems?

Spooling (Simultaneous Peripheral Operations On-Line) is a technique where output or input data for a slow device is first buffered onto a faster intermediate…

What is I/O Buffering and Why Is It Needed?

I/O buffering is the technique of holding data temporarily in an in-memory area while it moves between a process and a device, so the speed mismatch between fa…

What is the Dirty Bit in Paging?

The dirty bit (also called the modified bit) is a single flag in each page table entry that the hardware sets whenever a process writes to that page in memory,…

What is a Log-Structured File System?

A log-structured file system treats the entire disk as a single sequential append-only log, buffering all writes — data and metadata alike — into large segment…

What is the Buffer Cache in an Operating System?

The buffer cache is a region of kernel memory that holds recently used raw disk blocks so that repeated reads and writes to the same block hit fast RAM instead…

Page Cache vs Buffer Cache: What Is the Difference?

The page cache caches file contents in memory indexed by file and byte offset (used for regular file reads, writes, and mmap()), while the buffer cache histori…

What is Read Amplification in Storage Engines?

Read amplification is the ratio between the amount of data a storage engine actually reads from disk and the amount of data the application logically requested…