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From Stack <st...@duboce.net>
Subject Re: hbase get and mvcc
Date Tue, 17 May 2016 00:37:48 GMT
On Mon, May 16, 2016 at 5:19 PM, Shushant Arora <shushantarora09@gmail.com>
wrote:

> thanks!
>
> Does puts which fall inside readpoint of ongoing scan/get are preserved in
> HFile also or only in memstore and it blocks memstore flush until all
> ongoing scans are completed.
>
>
>
Yes.

If a flush happens while an outstanding Scan, the Put sequenceid -- the
sequenceid is a unique monotonically increasing id that is given to each
edit; this sequence id is assigned per region; this sequenceid is what mvcc
deals in -- makes it out to the hfile and is factored in when reads happen
to include the just-flushed hfile.

St.Ack




>
> On Tue, May 17, 2016 at 5:31 AM, Stack <stack@duboce.net> wrote:
>
> > On Mon, May 16, 2016 at 4:55 PM, Shushant Arora <
> shushantarora09@gmail.com
> > >
> > wrote:
> >
> > > Hi
> > >
> > > Hbase uses MVCC for achieving consistent result for Get operations .
> > > To achieve MVCC it has to maintain multiple versions of same row/cells
> .
> > > How many max version of a row/cell does Hbase keeps at any time to
> > support
> > > MVCC.
> > >
> > > Since say multiple gets started one after the other and has not
> completed
> > > yet and multiple puts are also occuring in between . Thus it maintains
> > all
> > > versions whose read point is still in use ?
> > >
> > >
> > Yes.
> >
> > All ongoing Gets/Scans are registered on startup with their current
> > readpoint (see HRegion; see constructor for HRegionScannerImpl). Any Put
> > that falls inside the readpoint of currently ongoing Gets/Scans will be
> > preserved while the Get/Scan is ongoing.
> >
> > St.Ack
> >
> >
> >
> > > Thanks!
> > >
> >
>

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