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https://issues.apache.org/jira/browse/NUTCH-2481?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Semyon Semyonov updated NUTCH-2481:
-----------------------------------
Component/s: (was: generator)
> HostDatum deltas(previous step statistics) and Metadata expressions
> -------------------------------------------------------------------
>
> Key: NUTCH-2481
> URL: https://issues.apache.org/jira/browse/NUTCH-2481
> Project: Nutch
> Issue Type: Improvement
> Components: hostdb
> Reporter: Semyon Semyonov
> Priority: Minor
>
> To allow the usage of previous step statistics(deltas of fetched,unfetced
> etc) in hostdb. The motivation is usage of this statistics in generate with
> maxCount expressions.
>
> The solution allows to fill in metadata of hostdatum based on custom JEXL
> expression using two hostdatum: before update(previousHostDatum) and after
> update(currentHostDatum)..
> For example to fill in difference in quantity of fetched at round t and t-1
> we can use the following expression
> <property>
> <name>hostdb.deltaExpression</name>
> <value>\{return new ("javafx.util.Pair","FetchedDelta",
> currentHostDatum.fetched - previousHostDatum.fetched);}</value>
> </property>
> A pull request will be provided shortly.
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