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Date: Fri, 6 Mar 2009 09:01:59 -0800 (PST)
From: "stack (JIRA)" <jira@apache.org>
To: hbase-dev@hadoop.apache.org
Subject: [jira] Commented: (HBASE-1246) BloomFilter's use of BitSet is too
 inefficient
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    [ https://issues.apache.org/jira/browse/HBASE-1246?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12679650#action_12679650 ] 

stack commented on HBASE-1246:
------------------------------

I thought this had been fixed?  See https://issues.apache.org/jira/browse/HBASE-427.  Maybe we lost Ian's fix down the line?

Also, up on IRC, Johano suggests:

{code}
09:59 < dj_ryan> hmm
09:59 < dj_ryan> we are going to have to write our own BitSet
09:59 < dj_ryan> the java one is too inefficient
09:59 < dj_ryan> it doesnt seem to actually use bits
09:59 < dj_ryan> it uses 1000 bytes to store 1000 bits
09:59 < dj_ryan> :-(
09:59 < dj_ryan> serialized the bitset is 160 bytes, but in memory its 10x bigger.
10:57 < johano> http://code.google.com/p/compressedbitset/
10:57 < johano> http://code.google.com/p/javaewah/
10:57 < johano> might be of use
{code}

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