[jira] [Commented] (HBASE-8635) Define prefetcher.resultsize.max as percentage

["Jimmy Xiang (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HBASE-8635?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13672280#comment-13672280 ] 

Jimmy Xiang commented on HBASE-8635:
------------------------------------

bq. worries me is all those users that already use 80% of their heap with BC and MemStores that won't be able to restart HBase once they upgrade because they'd now be at 90% with pre-fetching.

I will make sure prefetching is in checkForClusterFreeMemoryLimit. Fortunately, this is for 0.96.  I agree it is a concern, but it will be a little less of concern.

I think that the fixed number is not very nice, either 256MB or 128MB.  I think it is good to scale with the amount of memory given to HBase.  If this is not wanted, the percentage can be adjusted. BC is very helpful if data is accessed multiple times.  Prefetching, however, should help all the time.  As Anoop suggested, we can lower the default BC to 30%.

                
> 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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