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From "Elliott Clark (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-14978) Don't allow Multi to retain too many blocks
Date Tue, 15 Dec 2015 08:51:46 GMT

    [ https://issues.apache.org/jira/browse/HBASE-14978?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15057636#comment-15057636
] 

Elliott Clark commented on HBASE-14978:
---------------------------------------

bq.So with off heap Cells, withe very cell, we will treat it as coming from a new block?
Yep which bb controls which gets really interesting so I went with the more conservative.

bq.In fact with off heap Cell, which are delivered from L2 off heap cache, we wont get any
OOME issue
We won't get an OOME instead we'll kill the cache and be un-able to read anything from disk.
The end result is about the same. Disaster. Moving the data off heap doesn't really solve
any of the issues. It just means that we don't have the gc cleaning up. We have our own reference
counting.


> Don't allow Multi to retain too many blocks
> -------------------------------------------
>
>                 Key: HBASE-14978
>                 URL: https://issues.apache.org/jira/browse/HBASE-14978
>             Project: HBase
>          Issue Type: Improvement
>    Affects Versions: 2.0.0, 1.2.0, 1.3.0
>            Reporter: Elliott Clark
>            Assignee: Elliott Clark
>            Priority: Critical
>         Attachments: HBASE-14978-v1.patch, HBASE-14978.patch
>
>
> Scans and Multi's have limits on the total size of cells that can be returned. However
if those requests are not all pointing at the same blocks then the KeyValues can keep alive
a lot more data than their size.
> Take the following example:
> A multi with a list of 10000 gets to a fat row. Each column being returned in in a different
block. Each column is small 32 bytes or so.
> So the total cell size will be 32 * 10000 = ~320kb. However if each block is 128k then
total retained heap size will be almost 2gigs.



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