Re: [9fans] fossil woe

[Russ Cox <rsc@swtch.com>]

> of course. or don't call it a cache but "something that may
> fill up and screw you over".  the machine was far too hosed
> to connect to fscons and in any case telling a user "if you
> do too much stuff you will have to call me to fix fossil" is
> not aacceptable.

I'm not claiming, under any circumstances, that fossil
becoming unusable is acceptable.  However, the solution
is not as simple as "just write the blocks to venti".
First, writing blocks to venti requires some knowledge
of the rest of the file server state, and you can't always
write any block to venti.  Second, some people don't even
use venti and they can fill their fossils too.

There are plenty of subtle things going on in fossil that make
it much harder to handle the disk being full than in a conventional
file system.

Fossil needs some notion of being close to full, at which point
its behavior would change.  Automatic snapshots would stop,
as would mtime updates and any other source of automatic
dirtying of blocks.  There should be a few blocks reserved for
snapshots taken in response to manual console commands.
Then when fossil fills, you can remove recently written data
(if some runaway program has filled the disk) or connect to
the console and delete old snapshots or take an archival
snapshot.

If someone wants to work on making this happen, I would be
happy to provide further details.

Russ