[ZODB-Dev] Any risk about foreign zodb references

[Alexandre Garel]

Le 18/07/2011 18:16, David Glick a écrit :
> 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.

Thanks for the advice.

I normally won't fall in this case as my params objects are contained in 
parents and must exists even when all other zodb would not.

Thanks for your feedback.

-- 
Alex Garel