zotero.sqlite corruption caused by multiple reads?

[Graham Perrin]

I read a highlight from
http://www.zotero.org/support/dev/accessing_zotero_data_using_an_sqlite_client

> external access to the SQLite database … should only be
> done in a read-only manner.

alongside a highlight from
http://www.zotero.org/support/zotero_over_a_network

> multiple reads/writes can corrupt the Zotero library database

I can understand how multiple _concurrent writes_ might cause
corruption, but:

* how might corruption be caused by _multiple reads_?

TIA for advice
Graham

[Dan Stillman]

Concurrent reads wouldn't, of course, corrupt the database, but there
are a few additional issues that come into play when accessing Zotero
over the network:

1) If the auto-update preference is enabled, Zotero will still write to
the database during translator/style updates even if no manual changes
are made. So you'd want to enforce read-only access at the share level,
and you'd want to disable the pref (to prevent possible errors--I don't
know off-hand how well Zotero deals with a write failure during an update).

2) Zotero caches a lot of information in memory to improve performance,
so it won't really work as a traditional multi-user database
client--other clients wouldn't see many changes until restart.

3) Mozilla does some additional SQLite caching that may cause problems
if the database changes out from under it, so even if Zotero were
designed to account for external DB changes, mozStorage might not allow
for it, and it might even throw a (spurious) corruption error.

- Dan

[Graham Perrin]

Dan, many thanks.

Answers (1) and (2) paint a clear picture.

Answer (3) is equally good but (to me) not a concern; I don't
anticipate external (ex-Zotero) (ex-Mozilla) changes to the database.

[Dan Stillman]

On 12/29/08 5:53 AM, Graham Perrin wrote:
> Answer (3) is equally good but (to me) not a concern; I don't
> anticipate external (ex-Zotero) (ex-Mozilla) changes to the database.
>

I wasn't referring to changes outside Zotero, actually. From the
perspective of one of the read-only Mozilla clients, a write by another
Mozilla client would be an external change, changing the on-disk state
of the database from the in-memory representation.

[Graham Perrin]

Again, thanks: the picture is even clearer.

(AFAIR I found something to this effect in the documentation at
zotero.org but it's good to have it reaffirmed in this thread.)

I do not envisage a Mozilla client
but if I did: the client should be designed to never write to
zotero.sqlite
(assumes that Zotero is both added to, and enabled in, Mozilla).

(For users of Mozilla, Zotero add-on is certainly the preferred client
of zotero.sqlite.)

Best,
Graham