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https://issues.apache.org/jira/browse/HBASE-1246?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12679660#action_12679660
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Jonathan Gray commented on HBASE-1246:
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HBASE-427 fix is actually moving from a boolean[] to BitSet. BitSet has the
same space issues as the boolean[] so it didn't actually solve that.
compressedbitset is no go because it's GPL. Looked at javaewah but not clear
it's really what we want. It's not so much that we want to _compress_ the bit
array, we just want to store it efficiently. Generally compressing a bit array
retains efficiency in and/or operations but can be very poor at get() /
containment checks.
Streamy has a custom, stripped down implementation of blooms in java. We're
currently using BitSet but now learning about this space inefficiency I'd like
to move it to byte[]'s. Would that be worthwhile doing? Ryan, let me know
what you're working at so we can combine efforts.
> 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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