[Info-vax] VMS version numbers, was: Re: DCL enhancements

[Simon Clubley]

On 2021-01-28, Ji?í Ka?par <kaspaji3 at fit.cvut.cz> wrote:
> Shuffling when ;32767 is reached can be late.

Not really as it would be an atomic operation started when something
attempts to create another version. The create would stall until the
shuffling was complete and hence would never fail.

> We need a new file attribute to start autopurge:
>
> $ SET FILE x.y/SHUFFLE_LIMIT=n
> When version reaches the limit, shuffle autopurge starts asynchronously and application should be able to continue run and create new file versions over the limit.
>

Async is bad as it is not deterministic and there can be interaction issues
if something tries creating multiple new versions while this is in progress.

Much better and safer to stall the create of a new version until the
shuffling is complete.

> There is a question if there shoudn't be more general mechanism for triggering file events:
>
> $ SET FILE x.y/TRIGGER=event/ACTION=procedure
> Or maybe better to define/store it in ACL.
> But this can be security issue.
>

What you are looking for is a VMS version of inotify. It's been asked for
multiple times...

For those unaware: https://en.wikipedia.org/wiki/Inotify

There was also FAM: https://en.wikipedia.org/wiki/File_Alteration_Monitor

Simon.

-- 
Simon Clubley, clubley at remove_me.eisner.decus.org-Earth.UFP
Walking destinations on a map are further away than they appear.