Comment by Const-me | Hacker News Reader

Comment by Const-me | Hacker News Reader

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Windows kernel uses all free RAM as a file cache. Low priority one i.e. when an app wants to allocate RAM, the file system cached pages are evicted. Their Win7 test machine has 4GB RAM, Win10 16GB RAM.

I think I know what’s going on. They don’t publish absolute numbers, they only publish result compared to SQLight on the same machine. Windows has approximately fixed overhead when opening files. Most of that overhead goes to access checks, NTFS security descriptors are way more sophisticated than 9 bits of security in Linuxes. With a fast disk that overhead dominates in the cost, SQLight doesn’t open any files while running the test, the DB already opened at startup. With a slow disk, that overhead is masked by large IO cost which affects both SQLight and NTFS.

Nitpick, but file permissions in Linux take normally 12 bits. You probably did not count SUID, SGID and sticky bit.

I’ve only counted these famous RWX bits, settable by chmod. You’re right, there’s more security metadata involved in Linux.

Still, Windows permissions are way more complicated, especially when AD domains are involved. These access control lists have arbitrary count of entries each. There’s another list, SACL, for audit. Access permissions are inherited through file system with non-trivial inheritance rules, e.g. allow + deny = deny. User permissions are inherited through group membership, and security groups can be nested i.e. include other groups. Security descriptors may include custom permissions unknown to MS. Any thread can run as any user in the forest through client impersonation, many network servers do. The kernel tries to apply effective permissions instantly, as soon as anything changes (but not for every read/write, that would be too slow, it only does access checks when opening files).

Combined, these features make access checks way more expensive in Windows, by orders of magnitude.

Or the ACLs or extended attributes

https://linux.die.net/man/1/chattr

https://linux.die.net/man/1/setfacl

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