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https://issues.apache.org/jira/browse/NUTCH-466?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12485986
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Andrzej Bialecki commented on NUTCH-466:
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Minor nit: MapFile requires that the key is a WritableComparable.
I'm not sure I understand the last part of your comment .. There may be many
parts that use the same key/value classes in MapFiles. I think the API should
select the part by name (String) or some other ID, with a map of byte ID-s to
directory names (this is to avoid excessive overhead during RPC). Regarding the
implementing classes - I think we should use the plugin model, with a registry
of segment parts that are active for the current configuration.
> Flexible segment format
> -----------------------
>
> Key: NUTCH-466
> URL: https://issues.apache.org/jira/browse/NUTCH-466
> Project: Nutch
> Issue Type: Improvement
> Components: searcher
> Affects Versions: 1.0.0
> Reporter: Andrzej Bialecki
> Assigned To: Andrzej Bialecki
>
> In many situations it is necessary to store more data associated with pages
> than it's possible now with the current segment format. Quite often it's a
> binary data. There are two common workarounds for this: one is to use
> per-page metadata, either in Content or ParseData, the other is to use an
> external independent database using page ID-s as foreign keys.
> Currently segments can consist of the following predefined parts: content,
> crawl_fetch, crawl_generate, crawl_parse, parse_text and parse_data. I
> propose a third option, which is a natural extension of this existing segment
> format, i.e. to introduce the ability to add arbitrarily named segment
> "parts", with the only requirement that they should be MapFile-s that store
> Writable keys and values. Alternatively, we could define a
> SegmentPart.Writer/Reader to accommodate even more sophisticated scenarios.
> Existing segment API and searcher API (NutchBean, DistributedSearch
> Client/Server) should be extended to handle such arbitrary parts.
> Example applications:
> * storing HTML previews of non-HTML pages, such as PDF, PS and Office
> documents
> * storing pre-tokenized version of plain text for faster snippet generation
> * storing linguistically tagged text for sophisticated data mining
> * storing image thumbnails
> etc, etc ...
> I'm going to prepare a patchset shortly. Any comments and suggestions are
> welcome.
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