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POProcessing large XML file with libxml-ruby chunk by chunk
 

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    <p>I'd like to read a large <a href="http://dblp.uni-trier.de/xml/" rel="nofollow noreferrer">XML</a> file that contains over a million small bibliographic records (like <code>&lt;article&gt;...&lt;/article&gt;</code>) using libxml in Ruby. I have tried the Reader class in combination with the <code>expand</code> method to read record by record but I am not sure this is the right approach since my code eats up memory. Hence, I'm looking for a recipe how to conveniently process record by record with constant memory usage. Below is my main loop:</p> <pre><code> File.open('dblp.xml') do |io| dblp = XML::Reader.io(io, :options =&gt; XML::Reader::SUBST_ENTITIES) pubFactory = PubFactory.new i = 0 while dblp.read do case dblp.name when 'article', 'inproceedings', 'book': pub = pubFactory.create(dblp.expand) i += 1 puts pub pub = nil $stderr.puts i if i % 10000 == 0 dblp.next when 'proceedings','incollection', 'phdthesis', 'mastersthesis': # ignore for now dblp.next else # nothing end end end </code></pre> <p>The key here is that <code>dblp.expand</code> reads an entire subtree (like an <code>&lt;article&gt;</code> record) and passes it as an argument to a factory for further processing. Is this the right approach? </p> <p>Within the factory method I then use high-level XPath-like expression to extract the content of elements, like below. Again, is this viable?</p> <pre><code>def first(root, node) x = root.find(node).first x ? x.content : nil end pub.pages = first(node,'pages') # node contains expanded node from dblp.expand </code></pre>
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    1. USChristian Lindig
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      1. USLars Haugseth
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    1. COJust a small follow up: after some more testing with Ruby 1.8.7 on OS X 10.6 on x86 and Debian Linux on x86 I ran into seg faults on both machines while reading the XML file. I would guess the bug stems from libxml-ruby but I did not track it down so far. Quite disappointing.
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    2. COhttps://github.com/amolpujari/reading-huge-xml
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      1. USAmol Pujari
 

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