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HBase, mail # user - HBase 'Real-Time' reads?


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Jason Huang 2012-09-12, 21:15
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Adrien Mogenet 2012-09-12, 21:19
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Jason Huang 2012-09-12, 21:24
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Adrien Mogenet 2012-09-12, 21:28
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Re: HBase 'Real-Time' reads?
Jason Huang 2012-09-12, 21:35
I see now.

Thanks for the quick response and clear explanation.

Jason

On Wed, Sep 12, 2012 at 5:28 PM, Adrien Mogenet
<[EMAIL PROTECTED]> wrote:
> I think you misunderstand concept of "memstore". That's just the name of
> the temporary in-memory storage. Each region has its own memstore, and thus
> it's located on the regionserver itself.
>
> On Wed, Sep 12, 2012 at 11:24 PM, Jason Huang <[EMAIL PROTECTED]> wrote:
>
>> So - I guess at the time of the query we don't know if the data is in
>> Memstore or in the RegionServer. In order to ensure we get the most
>> recent version of data, every Hbase Read query will first go to
>> Memstore and see if the data is there, and then go to RegionServers if
>> it couldn't find that data in Memstore?
>>
>> thanks,
>>
>> Jason
>>
>> On Wed, Sep 12, 2012 at 5:19 PM, Adrien Mogenet
>> <[EMAIL PROTECTED]> wrote:
>> > 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 <[EMAIL PROTECTED]>
>> 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
>>
>
>
>
> --
> Adrien Mogenet
> 06.59.16.64.22
> http://www.mogenet.me