RE: [Zope-dev] Re: circular referenced persistent objects
[Sandor] > This is still a question. Is there any way, to determine how many > times a zodb persistent object is referenced? ZODB itself doesn't keep track of that, although it's possible to write a storage that does. FileStorage does not. BerkeleyStorage did (past tense because Zope Corp has given up on BerkeleyStorage for now). > sys.getrefcount seems to tell me only those references which are > currently loaded in the memory. Yes, sys.getrefcount() is a Python builtin, and only knows about in-memory Python objects. Python (and its builtins) doesn't know anything about persistence. > Also another very interesting question is that who referring > to a specific object. Like at the start, it would be possible to write a storage that saves away that kind of "inverted index", but I don't know of any that do. Given a particular flavor of storage, and detailed knowledge of its implementation, you can write scripts to crawl over the storage and compute anything you like. For FileStorage, the standard tools fsrefs.py and fsdump.py illustrate two ways of picking apart an .fs file. ___ Zope-Dev maillist - [EMAIL PROTECTED] http://mail.zope.org/mailman/listinfo/zope-dev ** No cross posts or HTML encoding! ** (Related lists - http://mail.zope.org/mailman/listinfo/zope-announce http://mail.zope.org/mailman/listinfo/zope )
Re: [Zope-dev] Re: circular referenced persistent objects
On Mon, 12 Apr 2004 10:57:43 -0500 <[EMAIL PROTECTED]> wrote: > Casey, > > Thanks for the clarification. > > > > - Is there an equivalent of sys.getrefcount for ZODB persistent > > > objects? > > This is still a question. Is there any way, to determine how many > times a zodb persistent object is referenced? sys.getrefcount seems to > tell me only those references which are currently loaded in the > memory. Also another very interesting question is that who referring > to a specific object. Not from a given object. You would need to walk the forward references (which are tracked) of all the objects to find this out. I posted some code to do this from any starting object in the ZODB a long time ago. Search the mail archives if you're interested. > > > For this I got the oid of the object, > > > deleted it and than tried to get it back via the oid. The trick > > > is, that you'll only get a POSKeyError if you pack the database > > and flush > > > the cache. This latter one was not obvious for me. > > > > Such tricks are not necessary and cause your app to rely too > > much on the > > curent implementation of ZODB. Just let the database take care of > > this for you. > > I used this trick only for exploring ZODB behavior. The application > doesn't do any nasty tricks. ok. -Casey ___ Zope-Dev maillist - [EMAIL PROTECTED] http://mail.zope.org/mailman/listinfo/zope-dev ** No cross posts or HTML encoding! ** (Related lists - http://mail.zope.org/mailman/listinfo/zope-announce http://mail.zope.org/mailman/listinfo/zope )
RE: [Zope-dev] Re: circular referenced persistent objects
Casey, Thanks for the clarification. > > - Is there an equivalent of sys.getrefcount for ZODB persistent > > objects? This is still a question. Is there any way, to determine how many times a zodb persistent object is referenced? sys.getrefcount seems to tell me only those references which are currently loaded in the memory. Also another very interesting question is that who referring to a specific object. > > For this I got the oid of the object, > > deleted it and than tried to get it back via the oid. The trick is, > > that you'll only get a POSKeyError if you pack the database > and flush > > the cache. This latter one was not obvious for me. > > Such tricks are not necessary and cause your app to rely too > much on the > curent implementation of ZODB. Just let the database take care of this > for you. I used this trick only for exploring ZODB behavior. The application doesn't do any nasty tricks. Regards, Sandor ___ Zope-Dev maillist - [EMAIL PROTECTED] http://mail.zope.org/mailman/listinfo/zope-dev ** No cross posts or HTML encoding! ** (Related lists - http://mail.zope.org/mailman/listinfo/zope-announce http://mail.zope.org/mailman/listinfo/zope )
[Zope-dev] Re: circular referenced persistent objects
On Sat, 10 Apr 2004 14:11:56 -0500 <[EMAIL PROTECTED]> wrote: > I have the following setup (unrelated lines are omitted): > > class Deliverer(Folder): > def manage_afterAdd(self, item, container): > if item is self: > self.__ac_local_roles__ = dr_localroles(self) > > class dr_localroles(Persistent): > def __init__(self, dr): > self.dr = dr > > dr_localroles implements a few methods of the dictionary interface, so > I can always check the effective settings via the Security/local roles > zmi page. In order to computing roles, dr_localroles requires its > parent object instance (Deliverer), that's why I store a reference to > it as an attribute. > Question: > - Is there a way for dr_localroles to refer its parent without > holding > a reference to it or using weak reference? Yes, use acquisition. Make dr_localroles inherit from Acquisition.Implicit or Acquisition.Explicit. > - Is there an equivalent of sys.getrefcount for ZODB persistent > objects? Cycles like this will not be a problem for ZODB. When either object is deleted it will no longer be reachable from the root, regardless of cycles between them. When the database is packed, unreachable objects are removed. > Also a note for the archives: > I wanted to make sure that if I delete a Deliverer object, it will > indeed be removed from ZODB. Once you pack, yes. > For this I got the oid of the object, > deleted it and than tried to get it back via the oid. The trick is, > that you'll only get a POSKeyError if you pack the database and flush > the cache. This latter one was not obvious for me. Such tricks are not necessary and cause your app to rely too much on the curent implementation of ZODB. Just let the database take care of this for you. In any case, there is a (new) persistent weakref class in ZODB 3.3 which allows you to weakly refer to other persistent objects without causing them to stay in the database like normal references do. -Casey ___ Zope-Dev maillist - [EMAIL PROTECTED] http://mail.zope.org/mailman/listinfo/zope-dev ** No cross posts or HTML encoding! ** (Related lists - http://mail.zope.org/mailman/listinfo/zope-announce http://mail.zope.org/mailman/listinfo/zope )
