bug#43850: cuirass: inconsistent SQL queries execution time.

[Mathieu Othacehe]

Hey Maxim,

> Perhaps we should run 'vacuum' when invoking 'guix gc' or at some other
> key places (where lots of data gets removed from the DB).  There's also
> the auto_vacuum PRAGMA, which is not enabled currently:

Vacuuming periodically seems important, however, it didn't resulted in
noticeable improvements during high I/O pressure when I tested it.

I still think that we should vacuum periodically, even though it means
that all database writes are postponed during the duration of the
vacuuming.

Having a separate fiber in charge of that operation could work I guess.

Thanks,

Mathieu