[jira] [Updated] (NUTCH-2481) HostDatum deltas(previous step statistics) and Metadata expressions

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[jira] [Updated] (NUTCH-2481) HostDatum deltas(previous step statistics) and Metadata expressions

David Eric Pugh (Jira)

     [ https://issues.apache.org/jira/browse/NUTCH-2481?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Sebastian Nagel updated NUTCH-2481:
-----------------------------------
    Affects Version/s: 1.15

> 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
>    Affects Versions: 1.15
>            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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