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https://issues.apache.org/jira/browse/NUTCH-1113?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13868024#comment-13868024
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Sebastian Nagel commented on NUTCH-1113:
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Hi [~markus17], I've run your unit tests and also tried again to find anything
using test data used to verify NUTCH-1520: SegmentMerger works as expected (in
local mode). Strange why it only happens in distributed mode.
# "to ignore linked crawl datums completely" applies only to crawl_fetch dir,
ie. linked items from redirects?
# after looking again at SegmentMerger: What if both fetch_success and linked
datum are contained in one segment? That may happen if we find a redirect in
the same round the target is fetched (found the link before). We do not
consider this case by testing {{lastFname.compareTo(sp.segmentName) < 0}}. If
the linked datum comes first it is not overwritten by the fetch datum. I'll try
to verify this in a test unit.
> Merging segments causes URLs to vanish from crawldb/index?
> ----------------------------------------------------------
>
> Key: NUTCH-1113
> URL: https://issues.apache.org/jira/browse/NUTCH-1113
> Project: Nutch
> Issue Type: Bug
> Affects Versions: 1.3
> Reporter: Edward Drapkin
> Priority: Blocker
> Fix For: 1.9
>
> Attachments: NUTCH-1113-junit.patch, NUTCH-1113-junit.patch,
> NUTCH-1113-junit.patch, NUTCH-1113-junit.patch, NUTCH-1113-trunk.patch,
> merged_segment_output.txt, unmerged_segment_output.txt
>
>
> When I run Nutch, I use the following steps:
> nutch inject crawldb/ url.txt
> repeated 3 times:
> nutch generate crawldb/ segments/ -normalize
> nutch fetch `ls -d segments/* | tail -1`
> nutch parse `ls -d segments/* | tail -1`
> nutch update crawldb `ls -d segments/* | tail -1`
> nutch mergesegs merged/ -dir segments/
> nutch invertlinks linkdb/ -dir merged/
> nutch index index/ crawldb/ linkdb/ -dir merged/ (I forward ported the lucene
> indexing code from Nutch 1.1).
> When I crawl with merging segments, I lose about 20% of the URLs that wind up
> in the index vs. when I crawl without merging the segments. Somehow the
> segment merger causes me to lose ~20% of my crawl database!
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