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From "Anoop Sam John (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-8635) Define prefetcher.resultsize.max as percentage
Date Fri, 31 May 2013 04:07:21 GMT

    [ https://issues.apache.org/jira/browse/HBASE-8635?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13671127#comment-13671127
] 

Anoop Sam John commented on HBASE-8635:
---------------------------------------

HBaseConfiguration#checkForClusterFreeMemoryLimit()
{code}
float globalMemstoreLimit = conf.getFloat("hbase.regionserver.global.memstore.upperLimit",
0.4f);
      int gml = (int)(globalMemstoreLimit * CONVERT_TO_PERCENTAGE);
      float blockCacheUpperLimit =
        conf.getFloat(HConstants.HFILE_BLOCK_CACHE_SIZE_KEY,
          HConstants.HFILE_BLOCK_CACHE_SIZE_DEFAULT);
      int bcul = (int)(blockCacheUpperLimit * CONVERT_TO_PERCENTAGE);
      if (CONVERT_TO_PERCENTAGE - (gml + bcul)
              < (int)(CONVERT_TO_PERCENTAGE *
                      HConstants.HBASE_CLUSTER_MINIMUM_MEMORY_THRESHOLD)) {
          throw new RuntimeException(....)
		  ...
	  }
{code}
As per this check we need a memory of min 20%(other than the reserved max spaces) for the
functioning of RS. Now in the Trunk gloabl memstore upperlimit and block cache size are default
to 40% making sum to 80%. A default value of 10% to the prefetch scan should be accomodated
in this condition. 
We need to sacrifice 10% from the block cache?
                
> Define prefetcher.resultsize.max as percentage
> ----------------------------------------------
>
>                 Key: HBASE-8635
>                 URL: https://issues.apache.org/jira/browse/HBASE-8635
>             Project: HBase
>          Issue Type: Improvement
>            Reporter: Ted Yu
>            Assignee: Jimmy Xiang
>            Priority: Minor
>         Attachments: trunk-8635.patch
>
>
> Currently "hbase.hregionserver.prefetcher.resultsize.max" defines global limit for prefetching.
> The default value is 256MB.
> It would be more flexible to define this measure as a percentage of the heap.

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