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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (GIRAPH-1125) Add memory estimation mechanism to out-of-core
Date Tue, 27 Dec 2016 21:28:58 GMT

    [ https://issues.apache.org/jira/browse/GIRAPH-1125?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15781296#comment-15781296
] 

ASF GitHub Bot commented on GIRAPH-1125:
----------------------------------------

Github user dlogothetis commented on the issue:

    https://github.com/apache/giraph/pull/12
  
    Somehow the file MemoryEstimatorOracle.java wasn't committed. I pulled the most recent
changes, I can see the commit log (see below), but this file is missing.
    
    commit f5b685efa09b539b1f95925405723f7ac7b1dcea
    Author: Hassan Eslami <heslami@apache.org>
    Date:   Fri Dec 23 12:03:37 2016 -0600
    
        GIRAPH-1125
    
        Closes #12
    
    



> Add memory estimation mechanism to out-of-core
> ----------------------------------------------
>
>                 Key: GIRAPH-1125
>                 URL: https://issues.apache.org/jira/browse/GIRAPH-1125
>             Project: Giraph
>          Issue Type: Improvement
>            Reporter: Hassan Eslami
>            Assignee: Hassan Eslami
>
> The new out-of-core mechanism is designed with the adaptivity goal in mind, meaning that
we wanted out-of-core mechanism to kick in only when it is necessary. In other words, when
the amount of data (graph, messages, and mutations) all fit in memory, we want to take advantage
of the entire memory. And, when in a stage the memory is short, only enough (minimal) amount
of data goes out of core (to disk). This ensures a good performance for the out-of-core mechanism.
> To satisfy the adaptiveness goal, we need to know how much memory is used at each point
of time. The default out-of-core mechanism (ThresholdBasedOracle) get memory information based
on JVM's internal methods (Runtime's freeMemory()). This method is inaccurate (and pessimistic),
meaning that it does not account for garbage data that has not been purged by GC. Using JVM's
default methods, OOC behaves pessimistically and move data out of core even if it is not necessary.
For instance, consider the case where there are a lot of garbage on the heap, but GC has not
happened for a while. In this case, the default OOC pushes data on disk and immediately after
a major GC it brings back the data to memory. This causes inefficiency in the default out
of core mechanism. If out-of-core is used but the data can entirely fit in memory, the job
goes out of core even though going out of core is not necessary.
> To address this issue, we need to have a mechanism to more accurately know how much of
heap is filled with non-garbage data. Consequently, we need to change the Oracle (OOC policy)
to take advantage of a more accurate memory usage estimation.



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