Fwd: Using sendfile with lmdb

To: openldap-devel@openldap.org

Subject: Fwd: Using sendfile with lmdb

From: James Rouzier <rouzier@gmail.com>

Date: Thu, 2 Apr 2015 22:55:21 -0400

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Eric thank you I would have never considered that as an issue.

I tried out your code and saw the problem.

You saved me going down a rabbit hole.

Many Thanks

On Thu, Apr 2, 2015 at 5:33 PM, Eric Wong <e@80x24.org> wrote:

James Rouzier <rouzier@gmail.com> wrote:
> Hey Guys,
>
> I am working on a proof of concept of a simple key value store service
> using lmdb as the back end.
> I am using sendfile to avoid an extra copy.

Be careful if you're overwriting any data in LMDB.

zero-copy sendfile means any data queued up in the kernel will be
subject to modifications as the underlying file is updated, so your
client may se data it was not intended to see.

I wanted to do the same thing as you last year but ended up writing a
patch to the sendfile manpage instead:

https://git.kernel.org/cgit/docs/man-pages/man-pages.git/patch?id=7b6a3299776b5c1c4f169a591434a855d50c68b4

References:

Using sendfile with lmdb
- From: James Rouzier <rouzier@gmail.com>
Re: Using sendfile with lmdb
- From: Eric Wong <e@80x24.org>