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From "stack (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-3455) Heap fragmentation in region server
Date Wed, 02 Feb 2011 05:55:29 GMT

    [ https://issues.apache.org/jira/browse/HBASE-3455?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12989524#comment-12989524
] 

stack commented on HBASE-3455:
------------------------------

+1

Minors below:

On commit, I wonder if you should commit w/ it disabled on branch but enabled on trunk?

In here:
{code}
+    // Use the internalAdd method here since we (a) already have a lock
+    // and (b) cannot safely use the MSLAB here.
+    // See TestMemStore.DISABLED_testUpsertMSLAB
{code}

... its not safe because it would bloat memory?  Or is it some thread 'safety' issue?  Maybe
clarify on commit?

Should this class even be public?

+public class MemStoreLAB {

Why this?

{code}
+    if (size > maxAlloc) {
+      return new Allocation(new byte[size], 0);
+    }
{code}

On return we'll clone when we don't need to?  Return null as flag that we're not to clone?
 (Caller is maybeCloneWithAllocator).

We should open new issue for fixing upsert?



> Heap fragmentation in region server
> -----------------------------------
>
>                 Key: HBASE-3455
>                 URL: https://issues.apache.org/jira/browse/HBASE-3455
>             Project: HBase
>          Issue Type: Brainstorming
>          Components: performance, regionserver
>    Affects Versions: 0.90.1
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>            Priority: Critical
>             Fix For: 0.90.1
>
>         Attachments: HBasefragmentation.pdf, collapse-arrays.patch, icv-frag.png, mslab-1.txt,
mslab-2.txt, mslab-3.txt, mslab-4.txt, mslab-5.txt, parse-fls-statistics.py, with-kvallocs.png
>
>
> Stop-the-world GC pauses have long been a problem in HBase. "Concurrent mode failures"
can usually be tuned around by setting the initiating occupancy fraction low, but eventually
the heap becomes fragmented and a promotion failure occurs.
> This JIRA is to do research/experiments about the heap fragmentation issue and possible
solutions.

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