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From "Paolo Castagna (JIRA)" <>
Subject [jira] [Created] (JENA-117) tdbloader2: Java external sorting using binary files vs. UNIX sort over text files
Date Mon, 19 Sep 2011 13:19:09 GMT
tdbloader2: Java external sorting using binary files vs. UNIX sort over text files

                 Key: JENA-117
             Project: Jena
          Issue Type: Improvement
          Components: TDB
            Reporter: Paolo Castagna

There is probably a significant performance improvement for tdbloader2 in replacing the UNIX
sort over text files with an external sorting pure Java implementation.
Since JENA-99 we now have a SortedDataBag which does exactly that.

    ThresholdPolicyCount<Tuple<Long>> policy = new ThresholdPolicyCount<Tuple<Long>>(1000000);
    SerializationFactory<Tuple<Long>> serializerFactory = new TupleSerializationFactory();
    Comparator<Tuple<Long>> comparator = new TupleComparator();
    SortedDataBag<Tuple<Long>> sortedDataBag = new SortedDataBag<Tuple<Long>>(policy,
serializerFactory, comparator);

TupleSerializationFactory greates TupleInputStream|TupleOutputStream which are wrappers around
DataInputStream|DataOutputStream. TupleComparator is trivial.

Preliminary results seems promising and show that the Java implementation can be faster than
UNIX sort since it uses smaller binary files (instead of text files) and it does comparisons
of long values rather than strings.
An example of ExternalSort which compare SortedDataBag vs. UNIX sort is available here:

A further advantage in doing the sorting with Java rather than UNIX sort is that we could
stream results directly into the BPlusTreeRewriter rather than on disk and then reading them
from disk into the BPlusTreeRewriter.
I've not done an experiment yet to see if this is actually a significant improvement.

Using compression for intermediate files might help, but more experiments are necessary to
establish if it is worthwhile or not.

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