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From "Lars Hofhansl (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-12023) HRegion.applyFamilyMapToMemstore creates too many iterator objects...
Date Fri, 19 Sep 2014 17:21:34 GMT

    [ https://issues.apache.org/jira/browse/HBASE-12023?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14140908#comment-14140908

Lars Hofhansl commented on HBASE-12023:

I mean random accessible as in tagged with the RandomAccess interface. LinkedList has a get(index)
but using that here would be very inefficient.

bq. (hopefully) will never be used in HBase
That's the worry I have. I've seen this happening in projects where folks expect an ArrayList
but sometimes get LinkedLists and then the performance tanks.

Or in other words we now created an implicit dependency on the Lists here being ArrayList.

The correct way would be to change the definition in Mutation to 
  protected NavigableMap<byte [], ArrayList<Cell>> familyMap =
    new TreeMap<byte [], ArrayList<Cell>>(Bytes.BYTES_COMPARATOR);

Then we're structurally guaranteed that we have ArrayLists and made the dependency explicit.
Of course now that will break binary compatibility and so we cannot just change it.

Anyway... If I'm the only one worrying about this, let's commit.

> HRegion.applyFamilyMapToMemstore creates too many iterator objects...
> ---------------------------------------------------------------------
>                 Key: HBASE-12023
>                 URL: https://issues.apache.org/jira/browse/HBASE-12023
>             Project: HBase
>          Issue Type: Bug
>    Affects Versions: 0.98.5, 0.94.23
>            Reporter: Vladimir Rodionov
>            Assignee: Vladimir Rodionov
>            Priority: Minor
>             Fix For: 0.94.24
>         Attachments: HBASE-12023-0.94.patch, HBASE-12023.patch, applyFamilyMapToMemstore
> for ... loop (creates iterator) inside another for loop. Produces a lot of garbage. See
attached picture.

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