Transitioning notmuch/Xapian from 32-bit to 64-bit system

Transitioning notmuch/Xapian from 32-bit to 64-bit system

[Thomas Schwinge]

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Hi!

Suppose you have a huge notmuch/Xapian database, built on a 32-bit system
(well, actually on x86_64-pc-linux-gnu, but using a years old 32-bit
notmuch binary; notmuch 0.9, Xapian 1.2.21 -- don't laugh), and suppose
you're finally going to update that years old notmuch installation
(release by release, forward-porting a bunch of patches).  Naturally, I'd
now do a native 64-bit build (unless somebody tells me a 32-bit build
would actually be preferable in terms of memory savings due to pointer
sizes?).  Doing some light (read-only!) testing, it seems to work fine to
access the old 32-bit built Xapian "chert" database with 64-bit
notmuch/Xapian.  Is that (a) generally safe and expected to work fine,
(b) there may be issues, or (c) don't do that, or don't know?

(Of course, I'll eventually want to rebuild the database, to take
advantage of several new features both on the notmuch and Xapian sides,
but I'd prefer to do that later.)


Grüße
 Thomas

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Re: Transitioning notmuch/Xapian from 32-bit to 64-bit system

[David Bremner]

Thomas Schwinge <thomas@schwinge.name> writes:

> sizes?).  Doing some light (read-only!) testing, it seems to work fine to
> access the old 32-bit built Xapian "chert" database with 64-bit
> notmuch/Xapian.  Is that (a) generally safe and expected to work fine,
> (b) there may be issues, or (c) don't do that, or don't know?
>

IIRC, Olly previously confirmed that the Xapian database is architecture
independent. I don't think notmuch uses xapian in any weird ways that
should break that.

It should work up to an 1.4.x release of Xapian and 0.29 of
notmuch. Xapian 1.5 (development) and 1.6 (future stable) will drop
support for chert.

> (Of course, I'll eventually want to rebuild the database, to take
> advantage of several new features both on the notmuch and Xapian sides,
> but I'd prefer to do that later.)
>

It would be wise to make a backup with "notmuch dump" before going much further.

Re: Transitioning notmuch/Xapian from 32-bit to 64-bit system

[Olly Betts]

On Tue, Jul 09, 2019 at 01:28:51PM -0300, David Bremner wrote:
> Thomas Schwinge <thomas@schwinge.name> writes:
> 
> > sizes?).  Doing some light (read-only!) testing, it seems to work fine to
> > access the old 32-bit built Xapian "chert" database with 64-bit
> > notmuch/Xapian.  Is that (a) generally safe and expected to work fine,
> > (b) there may be issues, or (c) don't do that, or don't know?
> 
> IIRC, Olly previously confirmed that the Xapian database is architecture
> independent.

Yes.

[...]
> 
> > (Of course, I'll eventually want to rebuild the database, to take
> > advantage of several new features both on the notmuch and Xapian sides,
> > but I'd prefer to do that later.)
> >
> 
> It would be wise to make a backup with "notmuch dump" before going much further.

You can convert the database at the Xapian level:

https://getting-started-with-xapian.readthedocs.io/en/latest/advanced/admin_notes.html#converting-a-chert-database-to-a-glass-database

However that probably doesn't allow taking advantage of all the new
notmuch features, so it's probably better to dump the tags, reindex
then restore the tags.

Cheers,
    Olly