[Info-vax] VMS databases

[Stephen Hoffman]

On 2023-11-18 14:22:52 +0000, Arne Vajhøj said:

> On 11/17/2023 8:10 PM, Arne Vajhøj wrote:
> 
> Niel Rieck replied (for some reason the post did not propagate to 
> eternal-september, so this is a manual copy from Google Groups):

Probably caught in the Google Groups spam.

>>  Two additional points.
>> 
>>  1) I've done a bit of hacking with SQLite (on both OpenVMS + Linux ) 
>> and can inform that it should only be used in single user applications. 
>> When any process issues an "update table" command, all other processes 
>> are locked out.
> 
> For multi user scenarios database servers are usually better than 
> embedded databases.

As with many things in IT, that depends.

Expectations and related sizes can also differ. What can be considered 
a small database for SQLite can potentially be considered a large 
database for OpenVMS, for instance.

Expectations? SQLite tops out at 256 TiB databases, while OpenVMS file 
storage tops out at 2 TiB files absent 'heroic' efforts.

> I would have thougth SQLite could only have locked some part of the 
> database when doing an UPDATE, but ...

If you ask nicely, SQLite will defer the locking until the commit:

https://sqlite.org/cgi/src/doc/begin-concurrent/doc/begin_concurrent.md

Otherwise, SQLite picks a simpler approach to database locking, 
permitting one concurrent writer.

That section also includes suggestions around how to arbitrate update 
access from within the application, when (if?) that becomes necessary.



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