bug#29654: Manual database index.db embeds timestamps

[Ricardo Wurmus <rekado@elephly.net>]

Hi Ludo,

> I was already motivated to create the database directly from Scheme
> (‘man-db’ is quite slow), so that gave me an additional excuse.  ;-)
>
> The attached patch does that.  The timestamps are always set to zero.

That’s great!

> Unfortunately, this is not fully deterministic: when running --check
> several times in a row, I occasionally get different results.  I suspect
> GDBM’s output is not fully deterministic.

Hmm, I dumped the contents of the generated databases with gdbm_dump and
couldn’t find any difference aside from the header (which is produced by
gdbm_dump itself).  Diffoscope shows a lot of differences, though.

I thought that maybe the difference comes from the fact that upon adding
new entries gdbm grows the hash table.  After setting the initial size
to a multiple of the number of entries I haven’t been able to generate a
non-reproducible database.

My only change is in “write-mandb-database”:

  (gdbm-open file GDBM_WRCREAT #:block-size (* 512 (length entries)))

I tried this:

    ./pre-inst-env guix package -p foo -i coreutils guile
    for i in `seq 30`; do ./pre-inst-env guix build --check -K /gnu/store/pg3684khpj69py40v7p76b90r9q4j2lv-manual-database.drv; done

Seems fine.  Coincidence or did I get lucky?

> +(define (entry->string entry)
> +  "Return the wire format for ENTRY as a string."
> +  (match entry
> +    (($ <mandb-entry> file name section synopsis)
> +     (string-append (abbreviate-file-name file) "\t"
> +                    (number->string section) "\t"
> +                    (number->string section)
> +
> +                    ;; Timestamps, that we always set to the epoch.
> +                    "\t0\t0"
> +
> +                    ;; XXX: Weird things.
> +                    "\tB\t-\t-\tgz\t"

What’s that?

-- 
Ricardo

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