Re: [sqlite] light weight write barriers

[Chris Friesen]

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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