[ZODB-Dev] Any risk about foreign zodb references

[David Glick]

On 7/18/11 9:08 AM, Alexandre Garel wrote:
> Hello,
>
> We are building up an application where we use multiple zodb instances.
> Indexation is done using solr.
> zodb are served through zc.zodbwsgi. ZODB connections are set only
> on-demand, upon traversal. Each zodb has its intid local utility. Each
> object also has a uuid.
>
> I have a zodb with global parameters objects on /params and distinct
> zodb as /foo /bar /baz and so on.
> Objects in a zodb may reference objects of the same zodb or of /params.
>
> I have two possible strategies :
>
> - either store uuid of referenced objects and retrieve objects from solr
> (which will give me a zodb name + intid of object)
> - either directly reference the objects of /params
>
> Of course second option seems better and more natural.
>
> I read
> http://svn.zope.org/ZODB/trunk/src/ZODB/tests/multidb.txt?rev=99605&view=markup
> and using pdb on databases = request.environ['zodb.connection'] I can
> see the zodb.databases map
> which is ok. I also know that _p_oid is unique and _p_jar handled for
> each object so I feel confident on this side.
>
> So before I dive into this, is this kind of cross-database reference
> used on production applications. Is there any-risk or any trick to be
> aware ?
Using cross-database references can be treacherous, because the garbage 
collection that occurs when packing a ZODB the typical way is not aware 
of the cross-db references. So if there's an object in one db that is 
only referenced from a different db, it will get garbage-collected 
during packing. You can probably use 
http://pypi.python.org/pypi/zc.zodbdgc instead of standard packing to 
avoid that problem.


----------		
David Glick
 Web Developer
 davidglick at groundwire.org
 206.286.1235x32

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