[Info-vax] VSI roadmap

[Arne Vajhøj]

On 8/23/2023 8:47 AM, David Jones wrote:
> On Tuesday, August 22, 2023 at 8:05:25 PM UTC-4, Arne Vajhøj wrote:
>> Are there some details that could have been done
>> different and better? Absolutely! Having record
>> size limit of 2 GB (32 bit length) instead of
>> 32 KB (16 bit length) would have been nice. If VAR
>> files has length both as line header and line trailer,
>> then such a file could easily be read backwards. I am
>> sure that if Hein could travel back in time he could
>> have optimized caching a lot. But wanting to change
>> some implementation details 45 years later is
>> no unique for RMS.
> 
> I'm not sure that's true, given how slow hardware was 45 years ago. Adding
> 6 bytes of meta-data to a VAR file with an average record length of 30
> characters will increase the size by 18%. More space on disk and more I/O
> operations to process the file.

I am not sure that I can follow the math.

Current VAR record overhead is header 2 bytes + average 0.5 even
pad byte and 2.5/30 is 8.3%.

Increasing to 32 bit would mean header 4 bytes + average 0.5 even
pad byte and 4.5/30 is 15.0%.

Increasing to 32 bit and add trailer length to support reading
backwards would mean header 4 bytes + average 0.5 even pad byte
+ trailer 4 bytes and 8.5/30 is 28.3%.

Yes - it is some overhead. But NOS/VE is almost as old as
VMS and used header 6 bytes and trailer 6 bytes. They could
apparently live with it.

Arne