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From NNever <nnever...@gmail.com>
Subject Re: Append and Put
Date Fri, 25 May 2012 03:38:52 GMT
Thanks J-D, good example.
Now it makes all clear to me. It helps a lot :)

NN

2012/5/24 Jean-Daniel Cryans <jdcryans@apache.org>

> On Wed, May 23, 2012 at 8:11 PM, NNever <nneverwei@gmail.com> wrote:
> > Thanks J-D.
> >
> > so it means 'Append' keeps write-lock only and 'Put' keeps
> > write-lock/read-lock both?
>
> Yeah... not at all. First, there's no read lock. Then Put is just a
> Put, it takes a write lock. Append is a read+write operation, still
> just uses a write lock.
>
> > and  if we use 'Append' instead of 'Put', then the chance Clients to wait
> > will reduce, right?
>
> You would use Append instead of Put only if you also need a Get. A
> typical example is a list, let's say you have a cell that's like:
>
> a,b,c
>
> Now you want to add ",d". Before Append you'd have to do a Get,
> manipulate the value (basically add the new data at the end) and then
> do a Put. That's 2 round trips. Append is just those operations put
> together and it runs all in the region server, saving you 1 round trip
> plus you don't have a race condition when you have multiple appenders
> on the same cell.
>
> Hope this helps,
>
> J-D
>

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