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From "Lukas Vlcek" <lukas.vl...@gmail.com>
Subject Re: Indexing and Re-crawling site
Date Wed, 13 Dec 2006 06:37:39 GMT
Hi,

One thing that I realized yesterday while looking into Hadoop code is that
as of now it is not possible to update existing file in HDFS. If I
understood it correctly then HDFS is write-once file system and you can not
update (add/remove content) to an existing file. Since Nutch can run on top
of HDFS it makes very sense to me why it works the way it does today.

Regards,
Lukas

On 12/5/06, Armel T. Nene <armel.nene@idna-solutions.com> wrote:
>
>
>
> Lukas,
>
> > This is more for Nutch experts but to me it seems that new index is
> > reasonable. Besides others it means that original index is still
> searchable
> > while the new index is being created (creating a new index can take long
> > time based on your settings). Updating one document at a time in large
> index
> > is not very optimal approach I think.
>
> I see your point but indexing could be a long process only if the all the
> files need to be re-fetched entirely. I don't know how this work, if the
> fetcher re-fetches everything and checks for the STATUS_UNMODIFIED before
> creating a segments out of it. The way I set it up at the moment is; the
> crawler will crawl a set of files at a time and so on but it also checks
> to
> see if the files held in the segments are up to date. My question is, when
> creating a new index, you said the old index will still be available until
> the new one is created, but what happens if someone is running a search
> while the IndexMerger is executing? I guess the old index gets deleted and
> replaced, does that mean an exception will be thrown while the index is
> being replaced?
>
> Regards,
>
> Armel
>
>
> -----Original Message-----
> From: Lukas Vlcek [mailto:lukas.vlcek@gmail.com]
> Sent: 04 December 2006 22:12
> To: nutch-dev@lucene.apache.org
> Subject: Re: Indexing and Re-crawling site
>
> Hi,
>
> I will try to use my out-dated knowledge to answer (& confuse you on) your
> items:
>
> 1.      Why does nutch has to create a new index every time when indexing,
> > while it can just merge it with the old existing index? I try to change
> > the
> > value in the IndexMerger class to 'false' while creating an index
> > therefore
> > Lucene doesn't recreate a new index each time it is indexing. The
> problem
> > with this is, I keep on having some exception when it tries to merge the
> > indexes. There is a lock time out exception that is thrown by the
> > IndexMerger. And consequently the index that get created. Is it possible
> > to
> > let nutch index by merging it with an existing index? I have to crawl
> > about
> > 100Gb of data and if there are only a few documents that have been
> > changed,
> > I don't nutch to recreate a new index because of that but update the
> > existing index by merging it with the new one. I need some light on
> this.
>
>
> This is more for Nutch experts but to me it seems that new index is
> reasonable. Besides others it means that original index is still
> searchable
> while the new index is being created (creating a new index can take long
> time based on your settings). Updating one document at a time in large
> index
> is not very optimal approach I think.
>
> 2.      What is the best way to make nutch re-crawl? I have implemented a
> > class that loops the crawl process; it has a crawl interval which is set
> > in
> > a property file and a running status. The running status is a Boolean
> > variable which is set to true if the re-crawl process is ongoing or
> false
> > if
> > it should stop. But with this approach, it seems that the index is not
> > being
> > fully generated. The values in the index cannot be queried. The re-crawl
> > is
> > in java which calls an underlying ant script to run nutch. I know most
> > re-crawl are written as batch script but can you tell me which one do
> you
> > recommended? A batch script or a loop-based java program?
>
>
> I used to use batch and was happy with it.
>
> 3.      What is the best way of implementing nutch has a window service or
> > unix daemon?
> >
>
> Sorry - what do you mean byt this?
>
> Regards,
> Lukas
>
>

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