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
