linux-kernel - Re: [sqlite] light weight write barriers

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Date:	Thu, 15 Nov 2012 16:35:47 -0600
From:	Chris Friesen <chris.friesen@...band.com>
To:	Ryan Johnson <ryan.johnson@...utoronto.ca>
CC:	General Discussion of SQLite Database <sqlite-users@...ite.org>,
	Vladislav Bolkhovitin <vst@...b.net>,
	Nico Williams <nico@...ptonector.com>,
	linux-fsdevel@...r.kernel.org, Theodore Ts'o <tytso@....edu>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Richard Hipp <drh@...ci.com>
Subject: Re: [sqlite] light weight write barriers

On 11/15/2012 11:06 AM, Ryan Johnson wrote:

> The easiest way to implement this fsync would involve three things:
> 1. Schedule writes for all dirty pages in the fs cache that belong to
> the affected file, wait for the device to report success, issue a cache
> flush to the device (or request ordering commands, if available) to make
> it tell the truth, and wait for the device to report success. AFAIK this
> already happens, but without taking advantage of any request ordering
> commands.
> 2. The requesting thread returns as soon as the kernel has identified
> all data that will be written back. This is new, but pretty similar to
> what AIO already does.
> 3. No write is allowed to enqueue any requests at the device that
> involve the same file, until all outstanding fsync complete [3]. This is
> new.

This sounds interesting as a way to expose some useful semantics to 
userspace.

I assume we'd need to come up with a new syscall or something since it 
doesn't match the behaviour of posix fsync().

Chris
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