[Info-vax] CRTL and RMS vs SSIO

[Dave Froble]

On 10/7/2021 8:54 AM, Greg Tinkler wrote:
>
>> Well the perceived issue is what happens when taking out locks, and at
>> some point there is a conflict. Say needing 127 blocks locked, and the
>> conflict is on the last block. That means 126 locks to be released, and
>> perhaps try again.
> Maybe, maybe not.  It depends on the locking fan out factors for the differing levels.  It is possible that only 1 lock is needed, may be more, the wort case would be 127.  NB there is also BLAST to assist with managing the lock promotion/demotions.
>
>
>> As long as storage is block oriented, then regardless of the numeric
>> range of bytes, all blocks encompassing the byte range will need to be
>> read, including locking, and written. This usually will include data
>> outside the byte range.
>
> Yup, as is the case on Unix...let the drivers worry about how and why this is done, block/byte what ever the IO device needs.
>
>> Forget RMS, I/O would be at the QIO level.
>
> Why?  Underneath RMS is QIO, what RMS gives us the the coordination of the buffers/buckets/clumps/block across the cluster to ensure not lost updates, as per the example used to justify SSIO.

Too limited and specific purpose.  RMS might be able to make use of some 
capabilities, but so might other applications.

RMS does some things well, and doesn't have some capabilities that it 
perhaps should have.  Data field definitions in records comes to mind.

>> RMS keyed files can have variable record lengths.
> True, VAR only not VFC or STM*, but fixed length key fields, with fixed offsets in the record
>
>> RMS relative files require fixed length records. (if I remember correctly)
> Yup, there are implicitly fixed length.
>
> ===
> Have been thinking about the byte range locking.  As most of the use will be for locking ranges in a file it should be integrated with RMS, i.e. RMS should have an API to allow this as it already does the locking to the buffer/bucket/clump/block.  Just need another 1 or 2 layers of lock tree and you have it.  And it all be cluster wide, and it will be compatible with other users of RMS.

Short sighted thinking.  Numeric range locking might be useful in many 
applications.


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David Froble                       Tel: 724-529-0450
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