Hassan Eslami created GIRAPH-1125:
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Summary: 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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