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Date: Mon, 28 Jun 2010 07:30:30 -0500
Message-ID: <AANLkTikeLVE1N9-EoyLBispZbcRUz1LXNOW47YYT3-lY@mail.gmail.com>
Subject: Re: "CommitLog" semantics
From: Gary Dusbabek <gdusbabek@gmail.com>
To: dev@cassandra.apache.org
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On Mon, Jun 28, 2010 at 04:44, Sriram Srinivasan <sriram@malhar.net> wrote:
> Hiya.
>
> The architecture internals document and various presentations (such as
> http://www.slideshare.net/jhammerb/data-presentations-cassandra-sigmod) s=
ay
> something like the following:
>
> =A0... a row mutation is first written to the commit log before being
> propagated to the memtable ...
>
> This gives the impression of traditional commitlog semantics found in
> databases and transaction managers, where a sync'd write is a confirmed
> state change.
>
> However, this is NOT the semantics of the code (db/Table.apply), which
> merely queues up a log request to be flushed, then directly proceeds to
> update the memtable. Which means it is possible for a client to receive a
> confirmation (even in a quorum case) before the data has been written to
> disk.
>
> Am I wrong?

In batch mode, we still block while the commit log is written.  See
BatchCommitLogExecutorService.add().  That add() method is what gets
called in Table.apply().

Gary.

>
> --sriram
>
>
>