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https://issues.apache.org/jira/browse/PHOENIX-4148?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16151238#comment-16151238
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Lars Hofhansl commented on PHOENIX-4148:
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My idea was to reserve a chunk of the HEAP (maybe in increments of 1MB), then 
allocate stuff onto the hashmap until the chunk is used up, at which point I'd 
request a new chunk. When finished all chunks would be released. Does that 
sound about right?

> COUNT(DISTINCT(...)) should have a memory size limit
> ----------------------------------------------------
>
>                 Key: PHOENIX-4148
>                 URL: https://issues.apache.org/jira/browse/PHOENIX-4148
>             Project: Phoenix
>          Issue Type: Bug
>            Reporter: Lars Hofhansl
>
> I just managed to kill (hang) a region server by issuing a 
> COUNT(DISTINCT(...)) query over a column with very high cardinality (20m in 
> this case).
> This is perhaps not a useful thing to do, but Phoenix should nonetheless not 
> allow to have a server fail because of a query.
> [~jamestaylor], I see there GlobalMemoryManager, but I do not quite see how 
> I'd get a reference to one, once needs a tenant id, etc.



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