Re: [Gnu-arch-users] [PATCH] arch speedups on big trees

[Miles Bader]

On Tue, Jan 06, 2004 at 04:20:19PM -0500, Chris Mason wrote:
> 1) Maintain a reverse mapping of ids to the objects that own them.  This
> lives in project_root/{arch}/++id-mapping, one file per id.

One file per id?!  That seems insane for large trees (the only case where
such optimizations are interesting anyway)...

> 3) Avoid inode signatures for everything except library revisions. 
> Since taking an inode signature involves a whole tree inventory, we
> should only take them when we know we're going to read them at least
> twice before snapping them again.  Otherwise, the inode sig is a net
> loss in speed

I assume this is done _only_ when someone specifies a list of filenames for
commit, i.e., whole-tree commits still make inode-sigs, right?

Actually even in the restricted-commit case, it seems like you could update
inode-sigs by simply reading an old inode-sigs file (if there is one), and
updating it to include the commited files.

[I've got to say I'm a bit worried by my vague impression I'm getting from
this dicussion: it seems like adding lots of little grotty hacks to speed up
specific special cases -- with the onus on the _user_ to give the magic
incantations required to hit the sweet spot -- and
ignoring/removing/screwing-with more general optimizations.

It's clear that there's a lot of non-optimal behavior by tla (I've lately
been trying to use tla on NFS-mounted filesystems, so I well understand
this), but it would be nice to see changes that improve things generally...]

-Miles
-- 
We have met the enemy, and he is us.  -- Pogo