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From Todd Lipcon <t...@lipcon.org>
Subject Re: Facebook messaging and choice of HBase over Cassandra - what can we learn?
Date Mon, 22 Nov 2010 03:15:49 GMT
On Sun, Nov 21, 2010 at 6:25 PM, Jonathan Ellis <jbellis@gmail.com> wrote:

> On Sun, Nov 21, 2010 at 6:16 PM, Todd Lipcon <todd@lipcon.org> wrote:
> > [only jumping in because info was requested - those who know me know that
> I
> > think Cassandra is a very interesting architecture and a better fit for
> many
> > applications than HBase]
>
> Hey Todd!  Good to see you de-lurk!
>
> Howdy :)

> > In the other mode of operation (default in recent versions of HBase) we
> do
> > not acknowledge a write until it has been pushed to the OS buffer on the
> > entire pipeline of log replicas.
>
> You mean "to the disk," I assume?
>
>
Actually just to the OS buffers. So if the entire cluster loses power
simultaneously you will lose data. If you lose just one rack, though, you'll
be OK since the pipeline always spans two racks in a multirack installation.

There are plans to add an API that fully fsync()s the replicas, but
currently there has been little demand - in memory on three replicas is
"safe enough" for most use cases, and of course a lot more performant.

-Todd

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