On Friday I posted a question about the performance of directory
lookups in NFS V3. Interestingly, the first 3 replies were:
1. A "me too", saying that Digital support had been no help with it.
2. A reply from somebody in Digital giving the answer.
3. A copy of a patch received from Digital.
Although nobody said so explicitly, it appears that my conjecture
about anticipatory attribute caching is correct, but there are kernel
variables that can be patched with dbx to disable it.
There appear to be two variables:
doreaddirplus Appears to control whether the server side gives
the attributes.
do_client_readdirplus Appears to control whether the client side asks
for the attributes.
Setting doreaddirplus to zero in the server or do_client_readdirplus
in the client will cause V3 getdirentries to behave like V2. These can
be changed with "dbx -k", using "assign" to change the running kernel
or "patch" to change the on-disc /vmunix. (Of course the latter will
go away if the kernel is rebuilt, so it's probably best to add a
startup script to change it at boot time).
Particular thanks to Lance Berc and John Jorgensen.
Now that we've got that one out of the way, we will continue to look
at other issues with V3. Initial tests suggest that it is slower than
V2 for simple writes, but further investigation is needed before I can
say anything definite.
--
Martyn Johnson maj_at_cl.cam.ac.uk
University of Cambridge Computer Lab
Cambridge UK
Received on Mon Jun 01 1998 - 15:15:34 NZST