[Info-vax] Byte range locking - was Re: Oracle on VMS

[BillPedersen]

On Monday, November 21, 2016 at 12:43:42 PM UTC-5, David Froble wrote:
> BillPedersen wrote:
> > On Sunday, November 20, 2016 at 11:21:11 PM UTC-5, David Froble wrote:
> >> BillPedersen wrote:
> >>
> >>> Well we do not yet have Postgres on VMS.  There are a couple stumbling points
> >>> that have gotten in the way.  Shared Stream IO to files to allow multiple
> >>> writers and byte-range locking in the same context as the SSIO.  There are
> >>> two features  which several "data" sharing applications running on Linux/Unix
> >>> quite often have in common and they are the biggest stumbling points of
> >>> getting these sorts of software to run on VMS effectively.
> >> I guess my first question is, how does *ix do byte range locking?  There is 
> >> nothing special about locking between cooperating tasks.  Just needs a good 
> >> design, and then implementation.  With the initial help of John Santos I've 
> >> implemented a locking system.
> >>
> >> The reason I've asked how *ix does the job is that it's my impression that to do 
> >> other than agreed upon fixed length data locks, it seems that otherwise would 
> >> have to know a bit more about the data.  That's a bit different from what I've 
> >> done in the past, and how the VMS DLM works.
> >>
> >> Got any specifications?
> > 
> > The API is via either fcntl() of flock() depending on the flavor of the day.
> 
> Bill, you must not get out much, I thought everyone knew that I don't do C, I 
> don't think of C, and if I trip over it I kick it.
> 
> :-)
> 

Now, now, now...

You asked for a specification... The link goes to a page that has no "C" on it, just English text...  It is a reasonable, external specification.

And, anyway, there are always translators of one time or another...


> > Issue with these and Samba is that fcntl() limits the range to 2^31 bytes, according to some documents I have read while Windows clients can request up to 
> > 2^32 or 2^64 bytes depending on the client.  So Samba has some other their own internal locking that I have to explore.
> 
> Yeah, I actually have started to think about this "thing", and if you're really 
> using individual bytes as the lowest unit of measure, then the numbers used are 
> going to get rather large.  Regardless if you actually convert to block numbers, 
> the byte IDs will require very large integers.
> 
> > But without a coordinated cache then that might not help much.  Since since
> > shared stream IO allows updating of non-overlapping regions in a block...
> 
> Well, as I understand it, today's disks can have a minimum cluster size of maybe 
> 8 blocks, but, while I'm not familiar how VMS does it, you can still read, and 
> update, individual 512 byte blocks.  VMS has always had to work with disk 
> cluster size.  I'm thinking that I need to get some understanding of how this is 
> implemented.  Possibly the same technique could be used for updates not on disk 
> block boundaries?
> 
> This is starting to grab my attention.  Maybe I should be afraid?

We I do keep trying to recruit...

Bill.