Re: [PATCH 0/7] oxenstored: improve transaction conflict handling

From: David Scott <dave@recoil.org>
To: Wei Liu <wei.liu2@citrix.com>
Cc: Jonathan Davies <jonathan.davies@citrix.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Jon Ludlam <jonathan.ludlam@citrix.com>,
	Euan Harris <euan.harris@citrix.com>,
	xen-devel@lists.xenproject.org
Subject: Re: [PATCH 0/7] oxenstored: improve transaction conflict handling
Date: Sat, 19 Mar 2016 11:30:26 +0000	[thread overview]
Message-ID: <073CDE9C-45D1-4D8A-8CAD-1BA838E2A37A@recoil.org> (raw)
In-Reply-To: <20160318163621.GC23307@citrix.com>

> On 18 Mar 2016, at 16:36, Wei Liu <wei.liu2@citrix.com> wrote:
> 
> On Fri, Mar 18, 2016 at 10:33:35AM -0400, Konrad Rzeszutek Wilk wrote:
>> On Thu, Mar 17, 2016 at 05:51:08PM +0000, Jonathan Davies wrote:
>>> This patch series makes a substantial improvement to oxenstored's transaction
>>> handling.
>>> 
>>> The original design of oxenstored assumed that a transaction would only ever
>>> span a small subtree. In practice this is rarely the case and means that other
>>> xenstore traffic overlapping with a transaction can cause it to fail with
>>> EAGAIN. This leads to significant performance problems with toolstack operations
>>> when there is a certain level of xenstore traffic coming from other sources.
>>> 
>>> Instead, we observe that, although the transaction may span a large subtree, it
>>> is very unlikely to read or write the same keys as other xenstore traffic. This
>>> observation leads to an improved transaction conflict-handling algorithm in
>>> which the transaction is replayed to check it is serializable. This approach is
>>> superior in performance.
>>> 
>>> The sixth patch is the main one that changes the way transaction conflicts are
>>> handled. The first five patches prepare the way by performing some refactoring
>>> and addition of infrastructure that allows for transactions to be replayed. The
>>> seventh patch adds some extra logging.
>> 
>> All the patches have quite the Reviewed-by list already so I would think
>> these can go in now?
>> 
> 
> We need an ack from Dave.

Thanks for the reminder!

Acked-by: David Scott <dave@recoil.org>

> But, FWIW, the result is impressive, and the changes are only internal
> to oxenstored, so I think it's pretty safe interface-wise or
> protocol-wise.

Indeed — thanks, Jonathan, for putting this together and thanks to Andrew, Jon and Euan for the review! I’ve wanted to see this work for ages, so I’m really pleased that it’s finally happened :-)

Cheers,
Dave
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