[OpenAFS] limit amount of uncommitted cache manager data?

[Russ Allbery]

Adam Megacz <megacz@cs.berkeley.edu> writes:

> I've noticed that when writing really large files with something like
> "cat .. | gzip > /afs/file" on a machine with a very large cache manager
> cache, several hundred megabytes of data can accumulate locally before
> being written back when close() is called.  In some cases, this can lead
> to write() calls being quite fast, but the final close() call takes an
> hour or more to return.  We (hcoop) would like to avoid this situation
> if possible.

> I assume that this amount of "unwritten" data cannot exceed the size of
> the cache -- and I guess if this happens, the application is blocked
> until enough StoreData's have happened to free up cache space.  Is there
> any way to get the CM to start this throttling earlier on?  Say, for
> example, when the amount of unwritten data reaches 50MB?  Unfortunately
> setting the cache size to 50MB is not an option -- this machine performs
> other tasks as well.

Can you convince your application to call fsync periodically?  If so,
that's the fastest and easiest solution.  fsync will write the data back
to the server.

-- 
Russ Allbery (rra@stanford.edu)             <http://www.eyrie.org/~eagle/>