[Info-vax] DIRCACHE hit rate.

[Richard B. Gilbert]

Jan-Erik Söderholm wrote:
> Hi.
> I have an 7.3-2 Alpha system where I think that
> the hit rate on the DIR-cache is way to low.
> 
> DS20 with 9GB disks in BA356 shelfs.
> 
> Here is what it typicaly looks like :
> 
>                        CUR     AVE   MIN      MAX
>  Dir Data (Hit %)     3.00    3.20  0.00    30.00
>      (Attempt Rate) 312.00  548.90  0.00  2460.00
> 
> 
> The ACP_DIRCACHE is at the moment at 4000 (blocks)
> but I have raised it to 10000 without any measurable
> improvment.
> 
> Yes, there are a few DIR's that are "large", but not
> *that* large, maybe 5-10.000 files and a few DIR files
> of 1-2000 blocks. Another thing is that all files
> are timestamped in the filename, so there are
> normaly only ;1 files.
> 
5-10,000 files is an extremely large directory in VMS!!

Your directories should be a MAXIMUM of 100 blocks in size if you want 
to get decent performance!

> My batch jobs create a number of temp files during
> processing and I've got a feeling that this is
> slowing them down a bit.

If the numbers of temp files are in the 5,000-10,000 range, you can be 
quite certain that it's slowing them down a bit.
> 
> Now, what I'd like to ask, is if anyone knows if
> this part of VMS has had any major improvments in
> the 8.x versions ? We are currently thinking of
> upgrading anyway, and it would be nice to know
> if these hit rates would improve simply by upgrading.
> 

I haven't heard of such.  This has been a known "limitation" in VMS for 
at least twenty years now.

Try redesigning the application in a more "VMS friendly" way.

Or use <obligatory retching noises> Unix.