Re: 02/09: guix: store: Make register-items transactional, register drv outputs

["Ludovic Courtès" <ludo@gnu.org>]

Hi reepca,

guix-commits@gnu.org skribis:

> commit 91cbfa8da90d8d1723da753c171a378dae13cb40
> Author: Caleb Ristvedt <caleb.ristvedt@cune.org>
> Date:   Wed Jan 30 17:03:38 2019 -0600
>
>     guix: store: Make register-items transactional, register drv outputs
>     
>     * guix/store/database.scm (SQLITE_BUSY, register-output-sql): new variables
>       (add-references): don't try finalizing after each use, only after all the
>       uses.
>       (call-with-transaction): New procedure.
>       (register-items): Use call-with-transaction to prevent broken intermediate
>       states from being visible. Also if item is a derivation register its
>       outputs (the C++ registering does this).
>       ((guix derivations)): use it for read-derivation-from-file and
>       derivation-path?
>     
>     * .dir-locals.el (call-with-transaction): indent it.

That looks interesting!

That’s really two changes: making a proper transaction, and registering
the outputs.  Could you make it two separate commits?

> +(define SQLITE_BUSY 5)

Please add a comment stating that this is missing in
Guile-SQLite3 0.1.0 (which we should consider fixing.)

> +(define (call-with-transaction db proc)
> +  "Starts a transaction with DB (makes as many attempts as necessary) and runs
> +PROC. If PROC exits abnormally, aborts the transaction, otherwise commits the
> +transaction after it finishes."

Please use imperative tense (“Start”, not “Starts”) and two spaces after
an end-of-sentence period.  I realize I’m nitpicking but I think that
can help make the process smoother as we go.

>  (define* (register-items items
>                           #:key prefix state-directory
>                           (deduplicate? #t)
> @@ -305,6 +336,22 @@ Write a progress report to LOG-PORT."
>      (define real-file-name
>        (string-append store-dir "/" (basename (store-info-item item))))
>  
> +    (define (register-derivation-outputs)
> +      "Register all output paths of REAL-FILE-NAME as being produced by
> +it (note this doesn't mean 'already produced by it', but rather just
> +'associated with it'). This assumes REAL-FILE-NAME is a derivation!"
> +      (let ((drv (read-derivation-from-file real-file-name))
> +            (stmt (sqlite-prepare db register-output-sql #:cache? #t)))
> +        (for-each (match-lambda
> +                    ((outid . ($ <derivation-output> path))
> +                     (sqlite-bind-arguments stmt
> +                                            #:drvpath to-register
> +                                            #:outid outid
> +                                            #:outpath path)
> +                     (sqlite-fold noop #f stmt)))
> +                  (derivation-outputs drv))
> +        (sqlite-finalize stmt)))

I don’t feel comfortable using (guix derivations) here because that’s
supposed to be a higher level of abstraction.  I don’t see any way
around it though.

Could you add a test in tests/store-database.scm for this bit?

> +        (when (derivation-path? real-file-name)
> +          (register-derivation-outputs))

For clarity I’d make it:

  (register-derivation-outputs (read-derivation-from-file real-file-name))

Otherwise LGTM.  I hope we can merge things piecemeal while preserving
existing functionality.

Could you send updated patches?

Thanks,
Ludo’.