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From Adrien Mogenet <adrien.moge...@gmail.com>
Subject Re: HBase 'Real-Time' reads?
Date Wed, 12 Sep 2012 21:19:33 GMT
WAL is just there for recover. Reads will meet the Memstore on their read
path, that's how LSM Trees are working.

On Wed, Sep 12, 2012 at 11:15 PM, Jason Huang <jason.huang@icare.com> wrote:

> This might be a naive question but I am not able to find a good answer
> from searching online.
>
> The online guide mentioned that "Puts and Deletes are collected into
> an in-memory structure called the MemStore. Before the MemStore is
> update the changes are written to a Write Ahead Log (WAL) to enable
> recovery in case a server crashes. When it reaches a certain size the
> MemStore is flushed to disk into StoreFile."
>
> So, if an application tried to query a certain piece of data that
> hasn't been flushed to disk into StoreFile yet, where is HBase
> designed to get that piece of data? Is it going to the Region servers
> and tried to get the previous version of this data, or is it smart
> enough to go to the MemStore or WAL to get the most recent version of
> data?
>
> thanks!
>
> Jason
>


-- 
Adrien Mogenet
06.59.16.64.22
http://www.mogenet.me

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