XFC cachinh of no_caching file ?

[Mark Hopkins_4 · Accepted solution]

Opps - you're right.

This problem was fixed after V7.3-1 shipped.
The original design had i/os marked nocache
allocating space in the cache (there were
good reasons for this at the time) and not
releasing the space when the I/O was complete. There were several things that
were done to fix this -
1) Write I/Os marked nocache (either because of the volume state, file state,
I/O size or directly marked) will bypass the
cache very early in the processing. (This
was already true for read I/Os).
2) At the completion of the I/O, if a
page doesn't contain valid data, the page is
released.

Sorry for the confusion. A kit for V7.3-2
containing this fix and other performance
enhancements should be available by tomorrow
morning Eastern Standard Time. This kit will
named VMS731_XFC-V0200.PCSI and replaces
the V0100 kit. The kit for V7.3 has been
available for about a week. I recommend
applying these kits. Note that these
include all the changes and enhancements made
to XFC for V7.3-2.

A work around in the meantime is to mount
the volume /nocache. For V7.3-1, this case
was treated correctly for write i/os.
Unfortunately, this has the nasty effect of
turning off the file system caches (i.e.
XQP).

The problem isn't quite as bad as it
appears. It turns out that the blocks added
to this file will be in the low end of the
LRU queue and so will be deposed prior to
valid blocks.

You're procedure for setting the file
attributes is correct. Setting the nocache
bit on the directory will cause new files
to inherit this attribute. It will not
affect existing files.

Sorry for the confusion,

Mark Hopkins

[DICTU OpenVMS]

Mark,

Thanks for your reply. We applied the patch yesterday (along with update 2, sys 5, acrtl 3, graphics 2 and partitioning 2). But it doens't seem to have solved the "problem". There are still a lot of pages allocated to the export file, which is marked no_cache...

I know that the file will be pushed out of the cache, when needed, but I actually don't wan't it to get into the cache in the first place... ;-) Mounting /nocache is a bad option, because the disk also contains files that take advantage of the cache...

The output :

$ sh mem /cach=(file=DISK$EXPDISK:*.*)
System Memory Resources on 8-JAN-2004 08:22:53.91

Extended File Cache File Statistics:

_$1$DGA714:[EXPORTS]ENTIRE_REP.EXP;1 (closed)
Caching is enabled, active caching mode is No Caching
Allocated pages 183141 Total QIOs 94329
Read hits 0 Virtual reads 0
Virtual writes 94329 Hit rate 0 %
Read aheads 0 Read throughs 0
Write throughs 94329 Read arounds 0
Write arounds 0

Total of 1 file for this volume

$ dir $1$DGA714:[EXPORTS] /cache

Directory $1$DGA714:[EXPORTS]

ENTIRE_REP.EXP;1 No_caching

Total of 1 file.


$ prod show hist /since=yes
----------------------------------- ----------- ----------- --------------------
PRODUCT KIT TYPE OPERATION DATE AND TIME
----------------------------------- ----------- ----------- --------------------
DEC AXPVMS VMS731_GRAPHICS V3.0 Patch Install 07-JAN-2004 18:59:51
DEC AXPVMS VMS731_XFC V2.0 Patch Install 07-JAN-2004 18:59:09
DEC AXPVMS VMS731_SYS V5.0 Patch Install 07-JAN-2004 18:58:38
DEC AXPVMS VMS731_PARTITIONING V2.0 Patch Install 07-JAN-2004 18:57:54
DEC AXPVMS VMS731_ACRTL V3.0 Patch Install 07-JAN-2004 18:57:21
DEC AXPVMS VMS731_UPDATE V2.0 Patch Install 07-JAN-2004 18:53:48
----------------------------------- ----------- ----------- --------------------

6 items found

[Mark Hopkins_4]

O my...

I've reproduced this here. I'll let you
know when I have more information.

Thanks for reporting this.

Mark

[Mark Hopkins_4]

I believe that I've identied the bug (not
in XFC). It was introduced in V7.3-1. I'm
not going to give any details in case I'm
wrong (2 wrong answers in one thread is
sending me home pretty humble).

If this is a sequential file, the following
will flush the pages for the file from
the cache. I think that the bug applies
to either non-shared, sequential files or
files open with deferred write enabled
(DFW).

$ open/read/share x x.x
$ close x

Let me know if this doesn't work. I'll look
for something better, but nothing comes to
mind.

I'll log a report, but it might help to
log a customer report as well.

Thanks for your patience and persistence.

Mark Hopkins

[Wim Van den Wyngaert]

I have 7.3 and have the same problem.
It's not solved by open+close.

But if I use the file it clearly isn't cached any more because hit rate decreases.

Wim