[Chandler-dev] help in resolving the filters-loading-items problem

[Grant Baillie]

On Jun 12, 2006, at 16:23, Andi Vajda wrote:

> A long standing performance bug is that some filter expressions  
> used by FilteredCollections use an expression that causes the  
> entire item (or more) to be loaded. Normally, this is not a problem  
> but it becomes one when the collection becomes part of another  
> collection and an index is created from scratch on the new  
> collection causing all the collections making it up to be iterated  
> for item UUIDs. For a FilteredCollection to return an member item's  
> UUID, it needs to first test whether the item is a member (unless  
> it has an index of its own) and that can cause the item (and  
> whatever else the filter expression needs to run) to get loaded.
>
> There are currently two collections in the Chandler source that  
> still use regular attribute access (hence loading the item) instead  
> of view.findValue(). This is because their filter relies on several  
> other items to come up with a True or False answer.
>
> To resolve this, I proposed a 'bequeatheTo' feature which is like  
> 'inheritFrom' but in reverse. Whenever a value in such an attribute  
> changes, the attribute(s) mentioned in its 'bequeatheTo' aspect  
> would be given that value as well. That way, these values could be  
> cached on the item being tested by the FilteredCollection, allowing  
> view.findValue() use thereby preventing the item from being loaded.

So, after some further discussion, it turns out bequeathTo isn't need  
here. There are 2 cases (of using view[] instead of view.findValue 
(s)) in parcels/osaf/__init__.py:

(1)
     eventsWithRemindersIncludingTrash = FilteredCollection.update(
         parcel, 'eventsWithRemindersIncludingTrash',
         source=events,
         filterExpression="getattr(view[uuid], 'reminders', None)",
         filterAttributes=['reminders'])

(2)
     masterFilter = "view[uuid].hasTrueAttributeValue('occurrences')  
and "\
                    "view[uuid].hasTrueAttributeValue('rruleset')"
     masterEvents = FilteredCollection.update(parcel, 'masterEvents',
         source = events,
         filterExpression = masterFilter,
         filterAttributes = ['occurrences', 'rruleset'])

The "view[uuid].hasTrueAttributeValue('rruleset')" case can be dealt  
with by the existing findValue(). The other two cases ('occurrences'  
and 'reminders') are trying to figure out if a refcollection is empty  
or not. So, Andi is going to add some API to the repository layer to  
do just that.


--Grant