yes, of course, the comments just one line above even encourages you to do so:

# note that some of the options listed here could be set in the
# corresponding hadoop site xml param file

For most use cases this value is ok. Only if you're using a parsing fetcher 
with many threads you
may need more Java heap memory. Note that this setting only applies to
a (pseudo-)distributed mode (running on Hadoop). In locale mode you can set the 
Java heap size via
the environment variable NUTCH_HEAPSIZE.

> What will be the impact?

That depends mostly on your Hadoop cluster setup. Afaik, the properties 
resp. mapreduce.reduce.java.opts will override mapred.child.java.opts on Hadoop 
2.x, so on a recent
configured Hadoop cluster
there is usually zero impact.

There is also a Jira issue open to make the heap memory configurable in 
distributed mode, see


On 12/7/18 3:08 PM, hany.n...@hsbc.com wrote:
> Hello,
> While checking the Nutch (1.15) crawl bash file, I noticed at line 211 that 
> 1000MB is statically set for java - > mapred.child.java.opts=-Xmx1000m
> Any idea why?, Can I change it?, What will be the impact?
> Kind regards,
> Hany Shehata
> Enterprise Engineer
> Green Six Sigma Certified
> Solutions Architect, Marketing and Communications IT
> Corporate Functions | HSBC Operations, Services and Technology (HOST)
> ul. Kapelanka 42A, 30-347 Kraków, Poland
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