In database storage architecture, an extent is defined as a contiguous section of disk space allocated to store data pages or segments. Does this definition accurately describe an extent?

Introduction / Context:
An extent is a low-level physical storage concept used by many database engines (for example, SQL Server, Oracle, PostgreSQL tablespaces with segment-like behavior) to manage space efficiently. Understanding extents helps DBAs reason about I/O patterns, fragmentation, growth, and capacity planning.

Given Data / Assumptions:

• We consider common DBMS implementations that allocate data in fixed-size pages/blocks.
• Extents group consecutive pages/blocks on disk.
• Goal is to reduce allocation overhead and improve sequential I/O.

Concept / Approach:
Instead of allocating individual pages each time a table or index grows, the DBMS requests a larger unit — an extent — consisting of a contiguous run of pages. Contiguity promotes sequential reads/writes, reduces fragmentation, and lowers metadata overhead because one allocation operation reserves multiple pages at once.

Step-by-Step Solution:
Recognize that a page/block is the fundamental I/O unit (e.g., 8 KB).Extents are made of multiple adjacent pages (e.g., 8 pages for 64 KB).When a table or index needs more space, the engine allocates another extent rather than a single page.Because pages in an extent are contiguous, scanning them incurs fewer random I/Os.This contiguous allocation defines what an “extent” is.

Verification / Alternative check:
Examine allocation maps or space usage DMVs for a given DBMS; you will observe that growth occurs by extent-sized chunks and that adjacent pages belong to the same extent identifier, confirming contiguity.

Why Other Options Are Wrong:
Noncontiguous by design (option b) contradicts the definition; while fragmentation may occur over time, each extent itself is contiguous. Log-only (option c) is incorrect; extents apply broadly to data and index allocations. Cloud-only (option d) is wrong; the concept predates cloud storage. Single-page (option e) misstates the unit; an extent is multi-page.

Common Pitfalls:
Confusing “contiguous extent” with “the whole object is contiguous.” Objects may span many extents; not all extents for one object remain adjacent. Also, page size and extent size are DBMS-specific; do not assume identical sizes across platforms.

Final Answer:
Applies — this definition is accurate