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From "Alexis (JIRA)" <>
Subject [jira] Updated: (GORA-20) Flush datastore regularly
Date Sun, 19 Dec 2010 00:11:01 GMT


Alexis updated GORA-20:

    Attachment: mapred-site.xml

I added a new org.apache.gora.mapreduceGoraRecordWriter class (GoraRecordReader already existed)

The configuration reads a "gora.buffer.limit" hadoop property. This allows the user to change
the 10000 default value. One needs to set it in the usual mapred-site.xml configuration file,
to be added $NUTCH_HOME/conf directory for example. See attached example.

I hope this feature is ok, otherwise I can revert it and stick with a constant, immutable
value equals to 10000.

> Flush datastore regularly
> -------------------------
>                 Key: GORA-20
>                 URL:
>             Project: Gora
>          Issue Type: New Feature
>          Components: storage
>            Reporter: Alexis
>         Attachments: gora.patch, mapred-site.xml
> Right now you need to explicitly call the flush method to make the IO operation happen,
or close the datastore.
> The issue is described here:
Click on the image to see it in real size and look at the Heap utilization on the top right
> Not everybody has infinite memory. In a Nutch fetch process, I usually run into trouble
after around 20k urls downloaded because it takes up all the memory, the Java Heap space being
set to 1G with a system that "only" has 1G RAM as well.
> The feature consists of allowing the datastore to be flushed regularly during the Hadoop
job's reducer, org.apache.gora.mapreduce.GoraReducer. We would just add a maxBuffer parameter,
which default value is 10000 for example and that you can override in org.apache.gora.mapreduce.GoraOutputFormat.
It indicates the maximum number of records buffered in memory before the next flush operation
occurs to actually write them in the datastore. This would actually be a member of the org.apache.hadoop.mapreduce.RecordWriter
extension returned by getRecordWriter method.
> An idea of the fix is suggested in the above link. 

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