[jira] [Created] (BOOKKEEPER-570) ReadAhead Cache Size Limit Comparing Should also Consider Overhead Memory Usage

["Fangmin Lv (JIRA)" <ji...@apache.org>]

Fangmin Lv created BOOKKEEPER-570:
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             Summary: ReadAhead Cache Size Limit Comparing Should also Consider Overhead Memory Usage
                 Key: BOOKKEEPER-570
                 URL: https://issues.apache.org/jira/browse/BOOKKEEPER-570
             Project: Bookkeeper
          Issue Type: Improvement
          Components: hedwig-server
            Reporter: Fangmin Lv
            Assignee: Fangmin Lv


Currently in hedwig, we only use message body size to compare with readahead
cache size setting to judge whether we need to obsolete old messages. From the
performance test we found that we need extral memory to store the message, the
overhead is not small. So the real hedwig memory occupied by these messages is
approximately can be calculated by :

RealOccupiedMemory = NumOfMessages * (MessageBodySize + OVERHEADPERMESSAGE)

If the messag body is small, then maybe the hedwig will run out of memory even
we have set a small readahead cache size.

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