Copy-on-Write, COW
Version 1.0.0 · Updated 2026-07-28
CORE DEFINITION
Copy-on-write (COW) is an optimization strategy in computer programming. Its core idea is that if multiple callers simultaneously request the same resource (such as memory or disk data storage), they all get the same pointer to the same resource until one caller attempts to modify the content, at which point the system actually clones a private copy for that caller, while other callers still see the original resource unchanged. This process is transparent to other callers. The main advantage is that if no caller modifies the resource, no private copy is created, so multiple callers can share the same resource for read-only operations.
SCAFFOLDING EFFECT
Reduce cognitive load
Copy-on-write (COW) is an optimization strategy in computer programming. Its core idea is that if multiple callers simultaneously request the same resource (such as memory or disk data storage), they all get the same pointer to the same resource until one caller attempts to modify the content, at which point the system actually clones a private copy for that caller, while other callers still see the original resource unchanged.
Anchor fast decisions
When creating a copy, do not immediately copy the resource; instead, share it. Only when a party attempts to modify does it actually copy (write-time split). The mechanism is "delayed separation" — maximize resource utilization through sharing, and only incur the copy cost when a real fork occurs.
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