> For the complete documentation index, see [llms.txt](https://til.notdu.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://til.notdu.com/database/intro-to-database-systems/buffer-pool-and-memory-management/os-page-cache.md).

# OS Page Cache

Most disk operations go through the OS API.

Unless you tell it not to, the OS maintains its own filesystem cache.

Most DBMSs use direct I/O (0\_DIRECT) to bypass the OS's cache.

* Redundant copies of pages
* Different eviction policies