[Info-vax] CRTL and RMS vs SSIO

[Arne Vajhøj]

On 10/6/2021 9:45 AM, Dave Froble wrote:
> On 10/6/2021 8:40 AM, Craig A. Berry wrote:
>> On 10/5/21 9:06 PM, Greg Tinkler wrote:
>>> An extra that could be added, if the file is RFM=fixed, and the C
>>> code  uses it that way with the same record length then use the
>>> SYS$GET/SYS$PUT so it will play nicely with an RMS access to those 
>>> files.
>>
>> I don't know the degree to which the current plan corresponds to the
>> original plan from a decade or so ago, but back then only stream files
>> were going to be supported by SSIO, which makes sense since the whole
>> point is locking byte ranges.
> 
> It has been my impression that for quite some time at HP, work on 
> specific requests tended to be very specific to that request, and failed 
> to consider capabilities as general to VMS.
> 
> The approach to SSIO appears to be an example of this.  Basically, do 
> the least required to achieve the specific result.  In the case of SSIO 
> the result appears to be rather useless, at least so far.

General is better than specific.

When not considering resources.

My impression is that VSI engineering resources are very limited - and
several orders of magnitudes smaller than DEC 40 years ago.

So when they have the choice of solving something 80% for 200 hours of
effort or 100% for 1000 hours of effort then ...

> For some years I've advocated a more general enhancement to the VMS DLM, 
> specifically, numeric range locking.  Such would address a basic issue 
> I've had with the VMS DLM for a rather long time.

> I've also suggested in the past that a simple enhancement to the DLM, 
> specifically the addition of a "type of lock" with the capability of 
> adding logic for specific "types" would solve the locking part of SSIO 
> and do so as a part of VMS, not as part of the CRTL.

That would make sense to me.

But I do not count.

> As for byte range I/O, I'm not sure what is and isn't possible with disk 
> drives.  It has been my impression that only whole block transfers are 
> possible.  Perhaps I've been wrong.  Perhaps SSDs have more flexibility.

No matter what the disk can do then the VMS file system is still
block oriented and I believe the system services take block offsets
not byte offsets.

Arne