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Posted to dev@nutch.apache.org by "Semyon Semyonov (JIRA)" <ji...@apache.org> on 2018/01/19 11:37:00 UTC
[jira] [Commented] (NUTCH-2481) HostDatum deltas(previous step
statistics) and Metadata expressions
[ https://issues.apache.org/jira/browse/NUTCH-2481?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16332139#comment-16332139 ]
Semyon Semyonov commented on NUTCH-2481:
----------------------------------------
An example of usage.
For example to use fetched deltas in generate.
1) To calculate FetchedDelta in the hostdb update
<property>
<name>hostdb.deltaExpression</name>
<value>\{return new ("javafx.util.Pair","FetchedDelta", currentHostDatum.fetched - previousHostDatum.fetched);}</value>
</property>
2) To use FetchedDelta in generate to not crawl the websites with FetchedDelta < 5
<property>
<name>generate.max.count.expr</name>
<value> if(fetched > 70 && FetchedDelta < 5 ) \{return new("java.lang.Double", 0);} else \{return conf.getDouble("generate.max.count", -1);} </value>
</property>
> 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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