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From mark harwood <markharw...@yahoo.co.uk>
Subject Re: Question regarding sorting and memory consumption in lucene
Date Wed, 15 Oct 2008 16:56:07 GMT


Further to our discussion - see below a class that measures the added construction cost and
memory savings for an optimised field value cache for a given index.
The optimisation here being initial use of byte arrays, then shorts, then ints as more unique
terms emerge.
I imagine the majority of "faceting" fields and, to a lesser extent sorting fields (e.g. dates)
have <= 65k  unique terms and therefore can stand to benefit from this.


Cheers
Mark


===========
Begin code.......



package lucene.sort;

import java.io.IOException;
import java.text.NumberFormat;
import java.util.Collection;
import java.util.Iterator;

import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.Term;
import org.apache.lucene.index.TermDocs;
import org.apache.lucene.index.TermEnum;
import org.apache.lucene.index.IndexReader.FieldOption;

/**
 * 
 * Test to measure cost of dynamically upgrading fieldcache from byte array to
 * short to int depending on index content term distribution.
 * Currently tests all fields in an index but probably better to measure a sensible subset
 * of fields ie those that are likely to be cached.
 * 
 * @author MAHarwood
 * 
 */
public class BenchmarkOptimisedFieldCacheConstruction
{
static long totalExtraCachingCostMilliseconds = 0;
static long totalRamBytesSaving = 0;
private static int shortRange = ((int) Short.MAX_VALUE + (int) Math
.abs(Short.MIN_VALUE));
private static int byteRange = ((int) Byte.MAX_VALUE + (int) Math
.abs(Byte.MIN_VALUE));
static NumberFormat nf = NumberFormat.getIntegerInstance();

public static void main(String[] args) throws Exception
{
nf.setGroupingUsed(true);

//! Change this to analyse your choice of index
IndexReader reader = IndexReader.open("/indexes/myTestIndex");
int numDocs = reader.maxDoc();
// Change the above value to fake the number of docs in the index (thereby
// increasing size of arrays manipulated in this test)
// int numDocs=30*1000*1000;

Collection fields = reader.getFieldNames(FieldOption.INDEXED);
for (Iterator iterator = fields.iterator(); iterator.hasNext();)
{
String fieldName = (String) iterator.next();
measureOptimisedCachingCost(reader, fieldName, numDocs);
}
System.out
.println("Caching all terms in this index in an optimised form would cost an extra "
+ totalExtraCachingCostMilliseconds
+ " millis "
+ "but save "
+ nf.format(totalRamBytesSaving)
+ " bytes RAM");
}

private static void measureOptimisedCachingCost(IndexReader reader,String field, int numDocs)
throws IOException
{
TermDocs termDocs = reader.termDocs();
TermEnum termEnum = reader.terms(new Term(field, ""));
int t = 0; // current term number

String[] mterms = new String[reader.maxDoc() + 1];

// an entry for documents that have no terms in this field
// should a document with no terms be at top or bottom?
// this puts them at the top - if it is changed, FieldDocSortedHitQueue
// needs to change as well.
mterms[t++] = null;

byte byteRefs[] = new byte[numDocs]; // up to 32 bits used to refer
// into term pool
short shortRefs[] = null;
int intRefs[] = null;
long totalConvertTimeForField = 0;

try
{
do
{
Term term = termEnum.term();
if (term == null || term.field() != field)
break;
// store term text
// we expect that there is at most one term per document
if (t >= mterms.length)
throw new RuntimeException("there are more terms than "
+ "documents in field \"" + field
+ "\", but it's impossible to sort on "
+ "tokenized fields");
mterms[t] = term.text();

termDocs.seek(termEnum);
while (termDocs.next())
{
int doc = termDocs.doc();
if (intRefs != null)
{
intRefs[doc] = t;
} else if (shortRefs != null)
{
// adjust number to make optimal use of negative range
// of values that can be stored
shortRefs[doc] = (short) ((short) t - Short.MAX_VALUE);
int storedT = shortRefs[doc] + Short.MAX_VALUE;
if (storedT != t)
{
System.err.println(storedT + "!=" + t);
}

} else
{
// adjust number to make optimal use of negative range
// of values that can be stored
byteRefs[doc] = (byte) ((byte) t - Byte.MAX_VALUE);
}

}
t++;
if ((byteRefs != null) && (shortRefs == null))
{
// More terms than can be accessed using a byte - move to shorts
if (t >= byteRange)
{
long millis = System.currentTimeMillis();
shortRefs = new short[numDocs];
short adjust = (Short.MAX_VALUE - (short) Byte.MAX_VALUE);
for (int i = 0; i < byteRefs.length; i++)
{
shortRefs[i] = (short) ((short) ((short) byteRefs[i]) - adjust);
}
long millisDiff = System.currentTimeMillis() - millis;
byteRefs = null;
totalConvertTimeForField += millisDiff;
}
} else
{
if (intRefs == null)
{
if (t >= shortRange)
{
//more terms than can be accessed using shorts - move to ints
long millis = System.currentTimeMillis();
intRefs = new int[numDocs];
int adjust = Short.MAX_VALUE;
for (int i = 0; i < shortRefs.length; i++)
{
intRefs[i] = (int) shortRefs[i] + adjust;
}
long millisDiff = System.currentTimeMillis()
- millis;
totalConvertTimeForField += millisDiff;
shortRefs = null;
}
}
}
} while (termEnum.next());
} finally
{
termDocs.close();
termEnum.close();
}
if (intRefs != null)
{
long ramBytesSaving = 0;
totalRamBytesSaving += ramBytesSaving;
System.out.println("Field " +field + " added cache load cost of "
+ totalConvertTimeForField
+ " millis with no RAM saving over current FieldCacheImpl");
} else
{
if (shortRefs != null)
{
long ramBytesSaving = numDocs * 2;
totalRamBytesSaving += ramBytesSaving;
System.out.println("Field " +field + " added cache load cost of "
+ totalConvertTimeForField + " millis but saved "
+ nf.format(ramBytesSaving)
+ " bytes RAM over current FieldCacheImpl");
} else
{
long ramBytesSaving = numDocs * 3;
totalRamBytesSaving += ramBytesSaving;
System.out.println("Field " +field + " added cache load cost of "
+ totalConvertTimeForField + " millis but saved "
+ nf.format(ramBytesSaving)
+ " bytes RAM over current FieldCacheImpl");
}
}
totalExtraCachingCostMilliseconds += totalConvertTimeForField;
}
}



      

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