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https://issues.apache.org/jira/browse/NUTCH-601?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12565848#action_12565848
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Susam Pal commented on NUTCH-601:
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The 'if (newIndex != index)' condition is just a check whether this is a new
crawl directory being constructed, or it is a recrawl on a previous crawl
directory.
If it is a new crawl directory being constructed, a few lines above this check,
there is another 'if (!fs.exists(index))' condition which will set the newIndex
= index = '/index'. So, if both newIndex and index are same, we know that it is
a new crawl directory and we need not delete old 'index' because it would not
be present.
If it is a recrawl over a previous crawl directory, newIndex = '/new_index' and
index = '/index'. Since they are different, it indicates that this is a recrawl
and thus after '/new_index' is created, it'll quickly replace the old '/index'
with the '/new_index'.
This seems fine to me.
If you want to avoid the possibility of having new segments with old index if
something bad happens, then I should delete both 'index' and 'indexes' even
before the generate call. But I didn't want to delete old 'index' so early. I
was trying to minimize the time for which 'index' directory is unavailable.
This would be helpful in case someone is running a recrawl on the same 'crawl'
directory which the web-gui is using to serve search results.
Please let me know what you feel about this.
> Recrawling on existing crawl directory using force option
> ---------------------------------------------------------
>
> Key: NUTCH-601
> URL: https://issues.apache.org/jira/browse/NUTCH-601
> Project: Nutch
> Issue Type: Improvement
> Affects Versions: 1.0.0
> Reporter: Susam Pal
> Priority: Minor
> Attachments: NUTCH-601v0.1.patch, NUTCH-601v0.2.patch
>
>
> Added a '-force' option to the 'bin/nutch crawl' command line. With this
> option, one can crawl and recrawl in the following manner:
> {code}
> bin/nutch crawl urls -dir crawl -depth 2 -topN 10 -threads 5
> bin/nutch crawl urls -dir crawl -depth 2 -topN 10 -threads 5 -force
> {code}
> This option can be used for the first crawl too:
> {code}
> bin/nutch crawl urls -dir crawl -depth 2 -topN 10 -threads 5 -force
> bin/nutch crawl urls -dir crawl -depth 2 -topN 10 -threads 5 -force
> {code}
> If one tries to crawl without the -force option when the crawl directory
> already exists, he/she finds a small warning along with the error message:
> {code}
> # bin/nutch crawl urls -dir crawl -depth 2 -topN 10 -threads 5
> Exception in thread "main" java.lang.RuntimeException: crawl already
> exists. Add -force option to recrawl.
> at org.apache.nutch.crawl.Crawl.main(Crawl.java:89)
> {code}
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