What is modification, and why do we care? (was Re: [Zope3-dev] Missing ObjectContentModifiedEvent)

[Jim Fulton]

Dieter Maurer wrote:
> Jim Fulton wrote at 2005-5-26 14:43 -0400:
> 
>>...
>>  Probably the indexes that we *most* want to avoid reindexing are
>>  text indexes.  We have a ISearchableText interface that we
>>  commonly adapt objects to to get the text to index.  We really
>>  can't predict how this text is computed.
> 
> 
> Then, we probably do something wrong...

That's always a possibility.  I think what we are doing is
pretty reasonable.  Perhaps you have other suggestions.

> 
>>...
>>  A safer strategy seems to me to be to have the indexes themselves
>>  responsible for detecting changes that they care about.  I'm
>>  pretty sure that some of the Zope 2 indexes are careful to avoid
>>  reindexing, or at least avoid updating indexes if indexed values
>>  haven't changed.
> 
> 
> Even computing the value for a text index (without any change
> to the index itself) can be very expensive: it may
> include expensive fetching of a large object,
> an expensive conversion (text extraction), expensive splitting
> and comparison to what is currently indexes.

Perhaps. It depends a lot on the application.

I suggest that, if this optimization is important, it might
be much easier and cleaner to make text extracttion and comparison
cheap, rather than, trying to solve the problem with a more complex
event model.

> I would not like this overhead for e.g. workflow state changes by
> default.

I think it would be very difficult to come up with rules
for deciding which events might effect a text value and which would not.
For example, I can easily imagine objects who's searchable text
depends on their workflow state.

Jim

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