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From mark harwood <markharw...@yahoo.co.uk>
Subject Re: Document links
Date Mon, 08 Nov 2010 19:52:53 GMT
I came to the conclusion that the transient meaning of document ids is too 
deeply ingrained in Lucene's design to use them to underpin any reliable 
linking.
While it might work for relatively static indexes, any index with a reasonable 
number of updates or deletes will invalidate any stored document references in 
ways which are very hard to track. Lucene's compaction shuffles IDs without 
taking care to preserve identity, unlike graph DBs like Neo4j (see "recycling 
IDs" here: http://goo.gl/5UbJi )


Cheers,
Mark


----- Original Message ----
From: Ryan McKinley <ryantxu@gmail.com>
To: dev@lucene.apache.org
Sent: Mon, 8 November, 2010 19:03:59
Subject: Re: Document links

Any updates/progress with this?

I'm looking at ways to implement an RTree with lucene -- and this
discussion seems relevant

thanks
ryan


On Sat, Sep 25, 2010 at 5:42 PM, mark harwood <markharw00d@yahoo.co.uk> wrote:
>>>Both these on disk data structures and the ones in a B+ tree have seek 
offsets
>>>into files
>>>that require disk seeks. And both could use document ids as key values.
>
> Yep. However my approach doesn't use a doc id as a key that is searched in any
> B+ tree index (which involves disk seeks) - it is used as direct offset into a
> file to get the pointer into a "links" data structure.
>
>
>
>>>But do these disk data structures support dynamic addition and deletion of
>>>(larger
>>>numbers of) document links?
>
> Yes, the slide deck I linked to shows how links (like documents) spend the 
>early
> stages of life being merged frequently in the smaller, newer segments and over
> time migrate into larger, more stable segments as part of Lucene transactions.
>
> That's the theory - I'm currently benchmarking an early prototype.
>
>
>
> ----- Original Message ----
> From: Paul Elschot <paul.elschot@xs4all.nl>
> To: dev@lucene.apache.org
> Sent: Sat, 25 September, 2010 22:03:28
> Subject: Re: Document links
>
> Op zaterdag 25 september 2010 15:23:39 schreef Mark Harwood:
>> My starting point in the solution I propose was to eliminate linking via any
>>type of key. Key lookups mean indexes and indexes mean disk seeks. Graph
>>traversals have exponential numbers of links and so all these index disk seeks
>>start to stack up. The solution I propose uses doc ids as more-or-less direct
>>pointers into file structures avoiding any index lookup.
>> I've started coding up some tests using the file structures I outlined and 
>will
>>compare that with a traditional key-based approach.
>
> Both these on disk data structures and the ones in a B+ tree have seek offsets
> into files
> that require disk seeks. And both could use document ids as key values.
>
> But do these disk data structures support dynamic addition and deletion of
> (larger
> numbers of) document links?
>
> B+ trees are a standard solution for problems like this one, and it would
> probably
> not be easy to outperform them.
> It may be possible to improve performance of B+ trees somewhat by specializing
> for the fairly simple keys that would be needed, and by encoding very short
> lists of links
> for a single document directly into a seek offset to avoid the actual seek, 
but
> that's
> about it.
>
> Regards,
> Paul Elschot
>
>>
>> For reference - playing the "Kevin Bacon game" on a traditional Lucene index 
>of
>>IMDB data took 18 seconds to find a short path that Neo4j finds in 200
>>milliseconds on the same data (and this was a disk based graph of 3m nodes, 
10m
>>edges).
>> Going from actor->movies->actors->movies produces a lot of key lookups and

the
>>difference between key indexes and direct node pointers becomes clear.
>> I know path finding analysis is perhaps not a typical Lucene application but
>>other forms of link analysis e.g. recommendation engines require similar
>>performance.
>>
>> Cheers
>> Mark
>>
>>
>>
>> On 25 Sep 2010, at 11:41, Paul Elschot wrote:
>>
>> > Op vrijdag 24 september 2010 17:57:45 schreef mark harwood:
>> >>>> While not exactly equivalent, it reminds me of our earlier discussion
>>around
>>
>> >>>> "layered segments" for dealing with field updates
>> >>
>> >> Right. Fast discovery of document relations is a foundation on which lots

>of
>>
>> >> things like this can build. Relations can be given types to support a 
>number
>>of
>>
>> >> different use cases.
>> >
>> > How about using this (bsd licenced) tree as a starting point:
>> > http://bplusdotnet.sourceforge.net/
>> > It has various keys: ao. byte array, String and long.
>> >
>> > A fixed size byte array as key seems to be just fine: two bytes for a field
>>number,
>> > four for the segment number and four for the in-segment document id.
>> > The separate segment number would allow to minimize the updates
>> > in the tree during merges. One could also use the normal doc id directly.
>> >
>> > The value could then be a similar to the key, but without
>> > the field number, and with an indication of the direction of the link.
>> > Or perhaps the direction of the link should be added to the key.
>> > A link would be present twice, once for each direction.
>> > Also both directions could have their own payloads.
>> >
>> > It could be put in its own file as a separate 'segment', or maybe
>> > each segment could allow for allocation of a part of this tree.
>> >
>> > I like this somehow, in case it is done right one might never
>> > need a relational database again. Well, almost...
>> >
>> > Regards,
>> > Paul Elschot
>> >
>> >
>> >>
>> >>
>> >>
>> >> ----- Original Message ----
>> >> From: Grant Ingersoll <gsingers@apache.org>
>> >> To: dev@lucene.apache.org
>> >> Sent: Fri, 24 September, 2010 16:26:27
>> >> Subject: Re: Document links
>> >>
>> >> While not exactly equivalent, it reminds me of our earlier discussion 
>around
>>
>> >> "layered segments" for dealing with field updates [1], [2], albeit this
is 
>a
>>bit
>>
>> >> more generic since one could not only use the links for relating 
documents,
>>but
>>
>> >> one could use "special" links underneath the covers in Lucene to
>>maintain/mark
>>
>> >> which fields have been updated and then traverse to them.
>> >>
>> >> [1]
>> >>
>>http://www.lucidimagination.com/search/document/c871ea4672dda844/aw_incremental_field_updates#7ef11a70cdc95384
>>
>>
>> >>
>> >> [2]
>> >>
>>http://www.lucidimagination.com/search/document/ee102692c8023548/incremental_field_updates#13ffdd50440cce6e
>>
>>
>> >>
>> >>
>> >> On Sep 24, 2010, at 10:36 AM, mark harwood wrote:
>> >>
>> >>> This slideshow has a first-cut on the Lucene file format extensions
>>required to
>>
>> >>>
>> >>> support fast linking between documents:
>> >>>
>> >>> http://www.slideshare.net/MarkHarwood/linking-lucene-documents
>> >>>
>> >>>
>> >>> Interested in any of your thoughts.
>> >>>
>> >>> Cheers,
>> >>> Mark
>> >>>
>> >>>
>> >>>
>> >>>
>> >>>
>> >>> ---------------------------------------------------------------------
>> >>> To unsubscribe, e-mail: dev-unsubscribe@lucene.apache.org
>> >>> For additional commands, e-mail: dev-help@lucene.apache.org
>> >>>
>> >>
>> >> --------------------------
>> >> Grant Ingersoll
>> >> http://lucenerevolution.org Apache Lucene/Solr Conference, Boston Oct 7-8
>> >>
>> >>
>> >> ---------------------------------------------------------------------
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>> >>
>> >>
>> >>
>> >>
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>> >>
>> >>
>> >>
>> >
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>> >
>>
>>
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>>
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