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https://issues.apache.org/jira/browse/LUCENE-1990?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12904560#action_12904560
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Toke Eskildsen commented on LUCENE-1990:
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I have discovered a bug in Packed32 and Packed64: When the number of bits
exceed 2^31, the setters and getters fail. This is due to a missing cast in the
calculation of the entry-point in the backing int/long-arrays.
In both Packed32 and Packed64 the line
{code}
final long majorBitPos = index * bitsPerValue;
{code}
is used in get as well as set. This should be
{code}
final long majorBitPos = (long)index * bitsPerValue;
{code}
in all 4 cases.
A unit test for this is
{code}
/*
Check if the structures properly handle the case where
index * bitsPerValue > Integer.MAX_VALUE
*/
public void testIntOverflow() {
int INDEX = (int) Math.pow(2, 30);
int BITS = 4;
Packed32 p32 = new Packed32(INDEX, BITS);
p32.set(INDEX-1, 1);
assertEquals("The value at position " + (INDEX-1)
+ " should be correct for Packed32", 1, p32.get(INDEX-1));
p32 = null; // To free 512MB
Packed64 p64 = new Packed64(INDEX, BITS);
p64.set(INDEX-1, 1);
assertEquals("The value at position " + (INDEX-1)
+ " should be correct for Packed64", 1, p64.get(INDEX-1));
}
{code}
One big problem with the unit-test is that it requires 2^30*4/8 bytes = 512MB
of heap. I am guessing that this makes it impossible to run in the standard
test-suite.
I am unsure as to how I should push this fix through. Should I create a new
JIRA issue? Make a patch against trunk? Or maybe a committer could just try the
test above and insert the fix in trunk?
> Add unsigned packed int impls in oal.util
> -----------------------------------------
>
> Key: LUCENE-1990
> URL: https://issues.apache.org/jira/browse/LUCENE-1990
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Index
> Affects Versions: Flex Branch
> Reporter: Michael McCandless
> Priority: Minor
> Fix For: 4.0
>
> Attachments: generated_performance-te20100226.txt,
> LUCENE-1990-te20100122.patch, LUCENE-1990-te20100210.patch,
> LUCENE-1990-te20100212.patch, LUCENE-1990-te20100223.patch,
> LUCENE-1990-te20100226.patch, LUCENE-1990-te20100226b.patch,
> LUCENE-1990-te20100226c.patch, LUCENE-1990-te20100301.patch,
> LUCENE-1990.patch, LUCENE-1990.patch, LUCENE-1990.patch,
> LUCENE-1990_PerformanceMeasurements20100104.zip, perf-mkm-20100227.txt,
> performance-20100301.txt, performance-te20100226.txt
>
>
> There are various places in Lucene that could take advantage of an
> efficient packed unsigned int/long impl. EG the terms dict index in
> the standard codec in LUCENE-1458 could subsantially reduce it's RAM
> usage. FieldCache.StringIndex could as well. And I think "load into
> RAM" codecs like the one in TestExternalCodecs could use this too.
> I'm picturing something very basic like:
> {code}
> interface PackedUnsignedLongs {
> long get(long index);
> void set(long index, long value);
> }
> {code}
> Plus maybe an iterator for getting and maybe also for setting. If it
> helps, most of the usages of this inside Lucene will be "write once"
> so eg the set could make that an assumption/requirement.
> And a factory somewhere:
> {code}
> PackedUnsignedLongs create(int count, long maxValue);
> {code}
> I think we should simply autogen the code (we can start from the
> autogen code in LUCENE-1410), or, if there is an good existing impl
> that has a compatible license that'd be great.
> I don't have time near-term to do this... so if anyone has the itch,
> please jump!
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