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https://issues.apache.org/jira/browse/NUTCH-1340?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13262121#comment-13262121
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Lewis John McGibbney commented on NUTCH-1340:
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Hi Ferdy. I am +1 for this going into 2.0. If you could do your usual and
provide a small Javadoc comment for the new method you introduce that would be
great.
> Increase scalability by only removing markers when they actually exist for
> DbUpdaterReducer
> -------------------------------------------------------------------------------------------
>
> Key: NUTCH-1340
> URL: https://issues.apache.org/jira/browse/NUTCH-1340
> Project: Nutch
> Issue Type: Improvement
> Reporter: Ferdy Galema
> Fix For: nutchgora
>
> Attachments: NUTCH-1340-v1.txt
>
>
> After applying GORA-120 (this already is a huge performance boost by itself)
> one of the major bottlenecks of the DbUpdaterReducer is the deletion of the
> markers. The update reducer simply sets every row to delete its markers. A
> lot of rows do not actually have the markers but the deletes are fired away
> in any case. Because the markers are already always on the input, a simple
> check to see if they exist greaty improves performance.
> In particular it is very expensive in HBase, because every single Delete
> inmediately triggers a connection to the regionservers. (They ignore the
> "autoflush=false" directive). Although deletes can be done in batch, this is
> currently not supported by Gora. For one it is very difficult to implement in
> the current HBaseStore with regard to multithreading, and secondly I noticed
> performance did not increase significantly.
> By performance debugging on a real life cluster this currently seems to be
> the biggest bottleneck of the DbUpdaterReducer. (Remember only after applying
> GORA-120)
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