Xapian discuss - Jun 2021 - How to recover from this permanent fatal error?

On Sat, Jun 5, 2021 at 8:45 PM Olly Betts <olly at survex.com>
wrote:
>
> On Sat, Jun 05, 2021 at 09:39:28AM -0500, Felipe Contreras wrote:
> > On Fri, Jun 4, 2021 at 9:43 PM Olly Betts <olly at survex.com>
wrote:
> > > I'd suggest trying this simple tool I wrote that can probably
rescue the
> > > tags from a broken notmuch database (the tags are the part
notmuch can't
> > > just recreate by reindexing):
> > >
> > >
https://git.xapian.org/?p=xapian;a=blob;f=README.notmuch;hb=refs/heads/notmuch-tag-rescue-hack
> >
> > I can't seem to build it:
> [...]
> > ./backends/documentinternal.h:339:29: error: ?numeric_limits? was not
> > declared in this scope
> >   339 |                 wdf_delta =
numeric_limits<Xapian::termcount>::max();
> >       |                             ^~~~~~~~~~~~~~
>
> Oh, that's a missing header include which older compilers seemed to
> not complain about - it was fixed on master a few months ago, and I've
> just merged master to the branch to pick up the fix so it should build
> now.
This is what I get:

% xapian-core/bin/xapian-check ~/mail/.notmuch/xapian/termlist.glass
termlist:
xapian-core/bin/.libs/lt-xapian-check: DatabaseCorruptError: Db block
overwritten - are there multiple writers?

-- 
Felipe Contreras

On Sat, Jun 05, 2021 at 11:40:58PM -0500, Felipe Contreras
wrote:
> % xapian-core/bin/xapian-check ~/mail/.notmuch/xapian/termlist.glass
> termlist:
> xapian-core/bin/.libs/lt-xapian-check: DatabaseCorruptError: Db block
> overwritten - are there multiple writers?
Ah - this tool currently requires the termlist table to be undamaged
enough to at least scan through.

You could try commenting out the body of GlassTable::set_overwritten()
in xapian-core/backends/glass/glass_table.cc so it keeps going instead
of throwing this exception, which might allow it to usefully recover
some or all tags.  If you (or anyone) try that and it works let me know
and I can patch the branch to emit a warning message and continue there.

If the postlist table is readable it'd be possible to rescue the tag
data from there instead, but that's more complicated to do because
the tags would need collating for each message.

Cheers,
    Olly