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From "clockfly (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HBASE-7885) bloom filter compaction is too aggressive for Hfile which only contains small count of records
Date Tue, 26 Feb 2013 05:24:15 GMT

     [ https://issues.apache.org/jira/browse/HBASE-7885?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

clockfly updated HBASE-7885:
----------------------------

    Fix Version/s:     (was: 0.94.5)
                   0.94.6
         Assignee: clockfly
    
> bloom filter compaction is too aggressive for Hfile which only contains small count of
records
> ----------------------------------------------------------------------------------------------
>
>                 Key: HBASE-7885
>                 URL: https://issues.apache.org/jira/browse/HBASE-7885
>             Project: HBase
>          Issue Type: Bug
>          Components: Performance, Scanners
>    Affects Versions: 0.94.5
>            Reporter: clockfly
>            Assignee: clockfly
>            Priority: Minor
>             Fix For: 0.94.6
>
>         Attachments: hbase_bloom_shrink_fix.patch
>
>
> For HFile V2, the bloom filter will take a initial size, 128KB. 
> When there are not that much records inserted into the bloom filter, the bloom fitler
will start to shrink itself to do compaction. 
> For example, for 128K, it will compact to 64K ->32K->16K->8K->4K->2K->1K->512->256->128->64->32,
as long as it think that it can be bounded by the estimate error rate. 
> If we puts only a few records in the HFile, the bloom filter will be compacted to too
small, then it will break the assumption that shrinking will still be bounded by the estimated
error rate. The False positive rate will becomes un-acceptable high. 
> For example, if we set the expected error rate is 0.00001, for 10 records, after compaction,
The size of the bloom filter will be 64 bytes. The real effective false positive rate will
be 50%.
> The use case is like this, if we are using HBase to store big record like images, and
binaries, each record will take megabytes. Then for a 128M file, it will only contains dozens
of records.
> The suggested fix is to set a lower limit for the bloom filter compaction process. I
suggest to use 1000 bytes.

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