bug#32190: Cuirass doesn't check if two subsequent jobs yield the same derivation

[ludo@gnu.org (Ludovic Courtès)]

Hi Clément,

Clément Lassieur <clement@lassieur.org> skribis:

> Consider the following table:
>
> CREATE TABLE Derivations (
>   derivation    TEXT NOT NULL,
>   evaluation    INTEGER NOT NULL,
>   job_name      TEXT NOT NULL,
>   system        TEXT NOT NULL,
>   nix_name      TEXT NOT NULL,
>   PRIMARY KEY (derivation, evaluation),
>   FOREIGN KEY (evaluation) REFERENCES Evaluations (id)
> );
>
>
> And the following code:
>
> (define (db-add-derivation db job)
>   "Store a derivation result in database DB and return its ID."
>   (catch 'sqlite-error
>     (lambda ()
>       (sqlite-exec db "\
> INSERT INTO Derivations (derivation, job_name, system, nix_name, evaluation)\
>   VALUES ("
>                    (assq-ref job #:derivation) ", "
>                    (assq-ref job #:job-name) ", "
>                    (assq-ref job #:system) ", "
>                    (assq-ref job #:nix-name) ", "
>                    (assq-ref job #:eval-id) ");")
>       (last-insert-rowid db))
>     (lambda (key who code message . rest)
>       ;; If we get a unique-constraint-failed error, that means we have
>       ;; already inserted the same (derivation,eval-id) tuple.  That happens
>       ;; when several jobs produce the same derivation, and we can ignore it.
>       (if (= code SQLITE_CONSTRAINT_PRIMARYKEY)
>           (sqlite-exec db "SELECT * FROM Derivations WHERE derivation="
>                        (assq-ref job #:derivation) ";")
>           (apply throw key who code rest)))))
>
> I think the above constraint can't happen because by definition a new
> job (for the same job_name) is produced at each evaluation.  So eval-id
> will be incremented every time.

I added it at the time because it did happen.  In a given eval, there
can be two jobs producing the same derivation (for instance a job called
“gcc” produces xyz-gcc-5.5.0.drv, and a job called “gcc-5.5.0” produces
the very same xyz-gcc-5.5.0.drv.)

> Also, the docs (and a comment in schema.sql) says:
>
>     Builds are not in a one to one relationship with derivations in
>     order to keep track of non deterministic compilations.
>
> But I think it doesn't make sense, because Guix won't try to build twice
> the same thing unless '--check' is used (which obviously isn't the
> case).

The rationale (that was back in Mathieu’s GSoC) was that sometimes, you
can have several builds logs for one derivation.  In Hydra this happens
if a build fails for some non-deterministic reason and then you click on
“Restart” in the hope that it’ll succeed this time.  ;-)  In this
situation Hydra keeps both build logs IIRC.

Anyway, I lean towards keeping only one build log, at least for now,
which is what guix-daemon does.

> So not only we have a huge Derivations table full of identical items,
> but we also ask Guix to build them and we store the results in the
> Builds table...
>
> Maybe the solution is to replace the (derivation, evaluation) primary
> key with (derivation), and only build the newly added derivations.
> WDYT?

I agree, we don’t need all these identical items, it makes no sense.

You can go ahead and clean that up!  ;-)

Thank you,
Ludo’.