Re: write ahead logging in standby (streaming replication)

Hi Greg and Fujii,

Just a point on terminology: there's a difference in the usage of
semi-synchronous between DRBD and MySQL semi-synchronous replication, which
was originally developed by Google.

In the Google case semi-synchronous replication is a quorum algorithm where
clients receive a commit notification only after at least one of N slaves
has received the replication event. In the DRBD case semi-synchronous means
that events have reached the slave but are not necessarily durable. There's
no quorum.

Of these two usages the Google semi-sync approach is the more interesting
because it avoids the availability problems associated with fully
synchronous operation but gets most of the durability benefits.

Cheers, Robert

On 11/12/09 9:29 PM PST, "Fujii Masao" <masao(dot)fujii(at)gmail(dot)com> wrote:

> On Fri, Nov 13, 2009 at 1:49 PM, Greg Smith <greg(at)2ndquadrant(dot)com> wrote:
>> Right, those are the possibilities, all four of them have valid use cases in
>> the field and are worth implementing.  I don't like the label
>> "semi-synchronous replication" myself, but it's a valuable feature to
>> implement, and that is unfortunately the term other parts of the industry
>> use for that approach.
>
> BTW, MySQL and DRBD use the term "semi-synchronous":
> http://forge.mysql.com/wiki/ReplicationFeatures/SemiSyncReplication
> http://www.drbd.org/users-guide/s-replication-protocols.html
>
> Regards,
>
> --
> Fujii Masao
> NIPPON TELEGRAPH AND TELEPHONE CORPORATION
> NTT Open Source Software Center
>
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