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Posted to user@hbase.apache.org by Linlin Du <li...@hotmail.com> on 2014/03/17 14:01:07 UTC
block cache size questions
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?
Third question:
Is it possible to tell from .META when a region was last read? If so, how?
Many thanks,
Linlin
Re: block cache size questions
Posted by Jean-Daniel Cryans <jd...@apache.org>.
On Mon, Mar 17, 2014 at 6:01 AM, Linlin Du <li...@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
>
>
>
>
>
Re: block cache size questions
Posted by Ted Yu <yu...@gmail.com>.
For #1, see
http://stackoverflow.com/questions/4667483/how-is-the-default-java-heap-size-determined
For #3, it is currently not possible.
Cheers
On Mon, Mar 17, 2014 at 6:01 AM, Linlin Du <li...@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?
>
> Third question:
> Is it possible to tell from .META when a region was last read? If so, how?
>
> Many thanks,
>
> Linlin
>
>
>
>
>