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From Jean-Daniel Cryans <jdcry...@apache.org>
Subject Re: block cache size questions
Date Mon, 17 Mar 2014 16:14:06 GMT
On Mon, Mar 17, 2014 at 6:01 AM, Linlin Du <linlindu2009@hotmail.com> wrote:

> Hi all,
>
> First question:
> According to documentation, hfile.block.cache.size is by default 40
> percentage of maximum heap (-Xmx setting). If -Xmx is not used and only
> -Xms is used, what will it be in this case?
>
> Second question:
> This 40% heap space is shared by all entities (stores). How much block
> cache is used by each store (entity)? Is it allocated on demand? If a
> region has never been read after the region server is up, will block cache
> be allocated for it?
>

The block cache stores blocks, which are chunks of an HFile, and are by
default around 64KB in size. Allocation is on-demand. Learn more here
http://hbase.apache.org/book.html#block.cache


>
> Third question:
> Is it possible to tell from .META when a region was last read? If so, how?
>
> Many thanks,
>
> Linlin
>
>
>
>
>

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