Mathijs Homminga wrote:
Hi everyone,
Our crawler generates and fetches segments continuously. We'd like to
index and merge each new segment immediately (or with a small delay)
such that our index grows incrementally. This is unlike the normal
situation where one would create a linkdb and an index of all segments
at once, after the crawl has finished.
The problem we have is that Nutch currently needs the complete linkdb
and crawldb each time we want to index a single segment.
The reason for wanting the linkdb is the anchor information. If you
don't need any anchor information, you can provide an empty linkdb.
The reason why crawldb is needed is to get the current page status
information (which may have changed in the meantime due to subsequent
crawldb updates from newer segments). If you don't need this
information, you can modify Indexer.reduce() (~line 212) method to allow
for this, and then remove the line in Indexer.index() that adds crawldb
to the list of input paths.
The Indexer map task processes all keys (urls) from the input files
(linkdb, crawldb and segment). This includes all data from the linkdb
and crawldb that we actually don't need since we are only interested in
the data that corresponds to the keys (urls) in our segment (this is
filtered out in the Indexer reduce task).
Obviously, as the linkdb and crawldb grow, this becomes more and more of
a problem.
Is this really a problem for you now? Unless your segments are tiny, the
indexing process will be dominated by I/O from the processing of
parseText / parseData and Lucene operations.
Any ideas on how to tackle this issue?
Is it feasible to lookup the corresponding linkdb and crawldb data for
each key (url) in the segment before or during indexing?
It would be probably too slow, unless you made a copy of linkdb/crawldb
on the local FS-es of each node. But at this point the benefit of this
change would be doubtful, because of all the I/O you would need to do to
prepare each task's environment ...
--
Best regards,
Andrzej Bialecki <><
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