Extended File Cache

[David Teixeira]

I'm running OpenVMS 7.3 on an Alpha ES45 and need to disable Extended File Cache. How would I go about this?

Any assistance would be greatly appreciated.

[Uwe Zessin · Accepted solution]

Set VCC_FLAGS = 0 to disable all cacheing or = 1 to enable the old-style VIOC.

[Ian Miller.]

why do you wish to do this?

[Uwe Zessin]

To make the system go slower?

Seriously, perhaps David has heard about problems in the initial XFC releases, but I think they have been fixed by now and ECOs, even for VMS V7.3, are available.

[Galen Tackett]

Perhaps there are reasons to turn off the cache.

Wouldn't it be possible to have access patterns such that the Extended File Cache would not help performance?

Or a memory-poor situation where the physical memory taken up by the cache could be better used for some other purpose?

Just some thoughts...

Galen

[Hein van den Heuvel]

I'd like to echo the WHY sentiment.

Galen Tackett wrote:
>>> "Perhaps there are reasons to turn off the cache."

In which case we would like to know WHY?
Perhaps we have a similar problem and do not realize it yet, or perhaps we are in a position to fix it or otherwise improve it.

>>> "Wouldn't it be possible to have access patterns such that the Extended File Cache would not help performance?"

There is a known 'pathelogical' case with CONVERTing very large (mutliple GBs) indexed files with small, odd sized buckets. For this purpose odd is = not a multiple of 8KB.
This has since been addresses, but the real solution was of course to use reasonable large bucketsize on really large files.
Too many customers leave the size at the original design point, say 6, where 10 years later in production they really need 24 or 32 blocks (still not really big).

>>> "Or a memory-poor situation where the physical memory taken up by the cache could be better used for some other purpose?

NO. The XFC will drop back if need be.

Regards,
Hein.

[David Teixeira]

Thank you for all your responses. Here is an exerpt from a report given to us from our software vendor. We are upgrading and it was recommended that we turn off the XFC.(note that the database we're upgrading is called CACHE [cash-ay])

"MEMORY UTILIZATION:
Node has 2 GB of memory, with 3% of that memory free. This could cause problems during and after the 3.0 upgrade. I would recommend turning off the Extended File Cache in VMS, as Cache does not use it, and at least .33 GB of memory is currently allocated to this feature. There has been expansion of the nonpaged dynamic memory, but with this little memory free, I would not recommend increasing NPAGEDYN."

Now my issue is that a while back I set VCC_flags to 0. But when I bounced the system, the settings did not stick. Does anyone know why this is happening?

[Ian Miller.]

David, how did you change vcc_flags?
You should put the new value in SYS$SYSTEM:MODPARAMS.DAT and run AUTOGEN.
Parhaps you changed VCC_FLAGS in SYSGEN then did WRITE ACTIVE but not WRITE CURRENT?

Cache database may not use the cache but everything else on the node does. The size of the cache is dependent on the amount of free memory and adjusts automagically.

If you are that short of free memory you should be looking at getting more or reducing MAXPROCESSCNT & BALSETCNT parhaps. Either way a look at your whole system is needed.

[David Teixeira]

Hi Ian,

I modified sys$system:modparams.dat and ran autogen but it's not working. VCC_flags is now set to 2 and the default is 2. Here is what my modparams.dat file looks like:

SCSSYSTEMID=1026
SCSNODE="PPSIDX"
VAXCLUSTER=0
MIN_KSTACKPAGES=3
WINDOW_SYSTEM = 1
MIN_NPAGEDYN = 1998848
vcc_flags=0
! End of Factory Installed Software settings
!
SHADOWING=2
SHADOW_SYS_UNIT=0
SHADOW_SYS_DISK=1
SHADOW_MAX_COPY=4
TAPE_ALLOCLASS=1
ALLOCLASS=1
WINDOW_SYSTEM=0 ! Turn Decwindows on
!
MAXPROCESSCNT=700 ! M/VX License + 30 + UCX Symbionts processes
BALSETCNT=MAXPROCESSCNT-2 ! MAXPROCESSCNT - 2 - LEAVE AS IS
MIN_GBLSECTIONS=700
MIN_SYSMWCNT=1763
MIN_WSMAX=146320
MIN_GBLPAGES=3749700 ! Stuart R Salzer, value before autogen.
MIN_GBLPAGFIL=225632 ! MINGBLPAGFIL = MIN_GBLPAGES
MIN_SYSMWCNT=1763 ! GBLPAGES / 128
!
TTY_DEFCHAR2=135170 ! Virtual Terminals
TTY_TIMEOUT=180 ! Virtual terminals ;changed 10-22-91 by JJV/IDX
TTY_ALTYPAHD=2064 ! NEW LATMASTER ;changed 01-31-92 by jjv/idx
MIN_ACP_WINDOW=80 ! RECOMMENDED BY Tuning Guide Dated 4/1/94 V1 page 1-3
MIN_CHANNELCNT=10000 ! RECOMMENDED BT DEC WHEN WE INCREASED TELNET SESSIONS
MMG_CTLFLAGS=0 ! RECOMMENDED BY Tuning Guide Dated 4/1/94 V1 page 1-3

[Ian Miller.]

are there any errors reported in SYS$SYSTEM:AGEN$PARAMS.REPORT ?

There are some entries in your modparams that look like historical entries from VAX/VMS (reference to LATMASTER for example which I think was VMS V5.4-x?) and the setting of MMG_CTLFLAGS.