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From Nils Adermann <nader...@naderman.de>
Subject Re: Lazy Fulltext Search
Date Tue, 15 Apr 2008 00:01:17 GMT
Hi,

I agree with Søren that this is not necessarily a good idea. It is not 
trivial for an indexer to figure out which view results changed. One 
method to so is storing all indexed view results and then comparing them 
to the updated view once the indexer is called. This is a needless waste 
of resources. Updating the view index based on changed documents is even 
more difficult. You would have to recompute the view at least partially 
to find out which view results changed. Given the reduce step this means 
that any number of documents, including unchanged ones could be 
involved. This creates a lot of work.

I think the problem we face here is different usage patterns of views. 
There are views which process a lot of data and which are based on 
documents that are updated frequently.  But they might only be read from 
infrequently. These views profit from JIT computation. However many 
applications use views which are infrequently updated but often queried 
or searched. Such views benefit from live updating. If an application 
allows searching data it nearly always means that the data will be read 
more frequently than it is updated. So in conclusion both methods (JIT 
and live updates) make sense for views. But search normally only needs 
the live update mechanism. I believe it should become configurable 
whether a view is updated immediately after a change or only after a 
query takes place. Fulltext search would always work on views with 
immediate updates. The indexer would be notified about the changed 
results. On views which delay updates, search would only work if the 
fulltext search provides a mechanism to compare the new view results to 
the old ones.

Cheers
Nils

Jan Lehnardt wrote:
>
> On Apr 12, 2008, at 12:06, Søren Hilmer wrote:
>> Hi
>>
>> Have you read Chris' response about letting the view engine call the 
>> indexer,
>> as it has the information needed for the indexer? As I understand the 
>> idea,
>> it will essentially keep the fulltext indexer and the views in sync.
>>
>> I like this idea and I believe the code for the indexer would be much 
>> simpler
>> and efficient.
>>
>> Also as the shift goes towards indexing views and not documents, it 
>> makes
>> sense that it is the View engine that triggers the indexer, right?
>
> The only problem here is that views are changed, when they are being 
> queried and not when documents are added. So you could end up with a 
> lot of not-indexed data because your view hasn't been queried. That 
> can be worked around, but I don't think it makes things any easier :)
>
> The design of the update notification is intentionally simple. We 
> expect the clients (the Indexer in this case) to be smart. We believe 
> that this makes the server code is more robust in that way.
>
>
>> I have to study the View engine, if I am to provide any code for 
>> this, though
>> (provided consensus blows in this direction).
>>
>> Have fun
>>   Søren
>> On Friday 11 April 2008 13:26, Jan Lehnardt wrote:
>>> On Apr 11, 2008, at 08:55, Søren Hilmer wrote:
>>>> Hi Jan
>>>>
>>>> It certainly would simplify configuration, allthough the
>>>> DbUpdateNotificationProcess setting ought to be retained as it is
>>>> potentially usefull for other stuff than indexing (can you have more
>>>> than
>>>> one of these, setup?)
>>>
>>> No, the update searcher will stay! :-)
>>>
>>>> I am also worried about responsetimes for searching, potentially the
>>>> indexing can take considerable time. With the current approach
>>>> indexing
>>>> can be done off peak hours and only searching is done at prime time.
>>>
>>> Right, if you want to be conservative with resources, you might want
>>> togo
>>> with my approach at the expense of possibly higher response times the
>>> first time things are searched for (as it is with views). I just
>>> wanted to make
>>> available my idea that fulltext indexing could be modelled after how
>>> views
>>> work, in case this is useful for a specific scenario.
>>>
>>> Cheers
>>> Jan
>>> -- 
>>>
>>>> Have fun
>>>> Søren
>>>> -- 
>>>> Søren Hilmer, M.Sc., M.Crypt.
>>>> wideTrail            Phone: +45 25481225
>>>> Pilevænget 41        Email: sh@widetrail.dk
>>>> DK-8961  Allingåbro  Web: www.widetrail.dk
>>>>
>>>> On Thu, April 10, 2008 23:32, Jan Lehnardt wrote:
>>>>> Heya,
>>>>> while thinking more about the fulltext implementation, I began to
>>>>> wonder why we don't model it after the view engine.
>>>>>
>>>>> At the moment, we have an Indexer waiting for update notifications
>>>>> and
>>>>> polling CouchDB for changes and a separate mechanism to register a
>>>>> fulltext query Searcher, that looks up things in the index.
>>>>>
>>>>> My proposed architectural change would be to trigger the Indexer from
>>>>> the Searcher module when a request comes in, just like views work.
>>>>> This would delay the creation of fulltext indexes until they are
>>>>> actually needed.
>>>>>
>>>>> The possible drawback though is, that when building the fulltext
>>>>> index
>>>>> is rather slow, old-style pre-calculation might be more feasible.
>>>>> View
>>>>> deal with that by requiring frequent requests (possibly cron-ed).
>>>>>
>>>>> This is not a proposal or anything, just a thought I wanted to share
>>>>> with those who work on fulltext integration.
>>>>>
>>>>> If you have any input on this, please let us know ;)
>>>>>
>>>>> Cheers
>>>>> Jan
>>>>> -- 
>>
>> -- 
>> Søren Hilmer, M.Sc., M.Crypt.
>> wideTrail            Phone:    +45 25481225
>> Pilevænget 41        Email:    sh@widetrail.dk
>> DK-8961  Allingåbro    Web:    www.widetrail.dk
>>
>


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