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From "ryan rawson (JIRA)" <j...@apache.org>
Subject [jira] Created: (HBASE-1246) BloomFilter's use of BitSet is too inefficient
Date Fri, 06 Mar 2009 10:05:57 GMT
BloomFilter's use of BitSet is too inefficient

                 Key: HBASE-1246
                 URL: https://issues.apache.org/jira/browse/HBASE-1246
             Project: Hadoop HBase
          Issue Type: Bug
    Affects Versions: 0.20.0
         Environment: Java 1.6, OSX 64 bit
            Reporter: ryan rawson
             Fix For: 0.20.0

>From the logfile run of TestBloomFilter with special SizeOf agent jar:

Writing bloom filter for: hdfs://localhost:64003/user/ryan/testComputedParameters/1278366260/contents/6159869037185296839
for size: 100
2009-03-06 01:54:25,491 DEBUG [RegionServer:0.cacheFlusher] regionserver.StoreFile$StoreFileWriter(319):
New bloom filter: vectorSize: 1175 hash_count: 5 numKeys: 100
Serialized bloomfilter size: 160
In memory bf size: 1248

As we can see, the bit vector is 1175 bits, and the serialized size is fairly compact - 160

But the in-memory size is nearly 10x bigger than it has to be.  Looking in BloomFilter we

  BitSet bits;

is the only field.

Clearly it seems the BitSet is using 1 byte = 1 bit.  That is an 8 time expansion of where
we should be.

Considering every HFile could potentially have a bloom filter, and bloom filters are more
likely to have bit vector sizes of 10,000-100,000, we should do something about this.  Aka:
write our own bit-set that uses byte[] and bit ops.

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