Xapian discuss - Jan 2010 - Latest revision and backwards compatibility

Greetings,

I've been wondering about the index format and backwards compatibility.

We're using the dev version (for chert) and each svn up means that any
indexes created prior to this revision cannot be read.  Is this purely a
cautious move to prevent errors, and, barring any obvious index format
changes, can I safely force the current revision to read existing indexes?
 eg, by commenting out the throw in
xapian-core/backends/chert/chert_version.cc.

Or is there a better way?

Thanks
Henry

On Thu, Jan 14, 2010 at 11:10:45AM +0200, henka at cityweb.co.za
wrote:
> I've been wondering about the index format and backwards compatibility.
> 
> We're using the dev version (for chert) and each svn up means that any
> indexes created prior to this revision cannot be read.
That's incorrect.  The format of a "development" backend (which
chert
currently is) may change incompatibly between releases, but this has only
happened twice so far in chert's history - see the comment in
chert_version.cc:

// 200804180       Chert debuts.
// 200903070 1.1.0 doclen bounds and wdf upper bound.
// 200912150 1.1.4 shorter position, postlist, record and termlist keys.
> Is this purely a
> cautious move to prevent errors, and, barring any obvious index format
> changes, can I safely force the current revision to read existing indexes?
>  eg, by commenting out the throw in
> xapian-core/backends/chert/chert_version.cc.
No - if we bump the version, there really has been an incompatible change.
> Or is there a better way?
I guess your last "svn update" spanned 2009-12-15?  For this
particular
change there's a xapian-chert-update utility which can upgrade a database
for you with about the same efficiency as xapian-compact (and the result
is compacted too).

In general you can upgrade using copydatabase to flint before upgrading
and again back to chert afterwards - see here for details (though this
talks about flint and quartz):

http://xapian.org/docs/admin_notes#converting-a-0-9-x-flint-database-to-work-with-1-0-y

Cheers,
    Olly