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https://issues.apache.org/jira/browse/PIG-167?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12581669#action_12581669
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Pi Song commented on PIG-167:
-----------------------------
PS. Initially I just tried to change LinkedList to ArrayList and reduce the
lock contention. Then I realized that it can be done like a generational way
easily so the generational thing is just a by-product.
> Experiment : A proper bag memory manager.
> -----------------------------------------
>
> Key: PIG-167
> URL: https://issues.apache.org/jira/browse/PIG-167
> Project: Pig
> Issue Type: Improvement
> Reporter: Pi Song
> Attachments: diagram.gif, MemManager0.patch
>
>
> According to PIG-164, I think we still have room for improvement:-
> 1) Alan said
> {quote}
> "It rests on the assumption that data bags generally live about the same
> amount of time, thus there won't be a long lived databag at the head of the
> list blocking the cleaning of many stale references later in the list."
> {quote}
> By looking at a line of code in SpillableMemoryManager
> {noformat}
> Collections.sort(spillables, new Comparator<WeakReference<Spillable>>() {
> {noformat}
> - Alan's assumption might be wrong after the memory manager tries to spill
> the list.
> - I don't understand why this has to be sorted and start spilling from the
> smallest bags first. Most file systems are not good at handling small files
> (specially ext2/ext3).
> 2) We use a linkedlist to maintain WeakReference. Normally a linkedlist
> consumes double as much memory that an array would consume(for pointers).
> Should it be better to change LinkedList to Array or ArrayList?
> 3) In SpillableMemoryManager, handleNotification which does a kind of I/O
> intensive job shares the same lock with registerSpillable. This doesn't seem
> to be efficient.
> 4) Sometimes I recognized that the bag currently in use got spilled and read
> back over and over again. Essentially, the memory manager should consider
> spilling bags currently not in use first.
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