Writes to the file mapped in memory are not necessarily immediate writes to the file on disk

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Quizplus · Accepted Answer

When a file is mapped into memory, changes made to the in-memory version may not be immediately written to the actual file on disk. Instead, the changes are cached in memory and periodically sync'd with the disk version. This means that writing to a mapped file can be faster than writing directly to a file on disk, but it also means that there is the potential for data loss in the event of a crash or other system failure before the changes have been sync'd to disk.

Writes to the File Mapped in Memory Are Not Necessarily