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From Stack <st...@duboce.net>
Subject Re: HBase row level cache for random read
Date Thu, 23 Aug 2012 22:28:11 GMT
On Thu, Aug 23, 2012 at 12:06 PM, Gen Liu <geliu@zynga.com> wrote:
>
>
> On 8/18/12 12:33 PM, "Stack" <stack@duboce.net> wrote:
>
>>On Fri, Aug 17, 2012 at 4:42 PM, Gen Liu <geliu@zynga.com> wrote:
>>> I assume block cache store compressed data,
>>
>>Generally its not, not unless you use block encoding.
> Can you be more specific on this?  Are you talking about
> https://issues.apache.org/jira/browse/HBASE-4218
> So this is only available in 0.94 then? Thanks.
>>
>>> one block can hold 6 rows, but in random read, maybe 1 row is ever
>>>accessed, 5/6 of the cache space is wasted.
>>> Is there a better way of caching for random read. Lower the block size
>>>to 32k or even 16k might be a choice.
>>>
>>
>>We don't seem to list this as an option in this section,
>>http://hbase.apache.org/book.html#perf.reading, but yes, if lots of
>>random reads, smaller block cache could make a difference.
>>

See release note in https://issues.apache.org/jira/browse/HBASE-4218
St.Ack

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