Subject: Making file-based getXent quicker
To: None <>
From: Darren Reed <>
List: tech-userlevel
Date: 03/19/2006 20:41:14
In a discussion about how NetBSD opens and closes nls files way too
often, it was brought up that there are similar problems with the
name-number files like /etc/services and /etc/protocols.

So the problem is, what to do about it?  How can they be made quicker?

One idea I'd like to discuss is what about using a shared memory map
that is published by a daemon ?  If the daemon isn't present or the
map is missing, fall back to the "slow approach."

The daemon would use kqueue events to know when it should refresh the
cache as changes to the files are made - this won't work if /etc or the
mount point the files come from isn't local.

The file created by the daemon would live in /var/run, perhaps a

This file would need to be opened and read only once in the lifetime
of a program.  The shared memory segment would act as an in-core
database (maybe 8k-16k) that get*name/get*by* would copy data out
of before returning it to the caller.  Some use of locking would
be required to keep people out while it is being updated.

Unfortunately I can't think of a better name for it than nscd.

What this solution means in the context of NIS/LDAP serving these
databases hasn't yet been considered yet.  But in a local files
approach, I can see the following being cached:


Other files?

Thoughts?  Comments?  Suggestions?  Flames?