linux-ext4 - Re: fsync() errors is unsafe and risks data loss

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Message-ID: <20180412050924.GO2801@thunk.org>
Date:   Thu, 12 Apr 2018 01:09:24 -0400
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     Andres Freund <andres@...razel.de>
Cc:     Dave Chinner <david@...morbit.com>,
        Andreas Dilger <adilger@...ger.ca>,
        Ext4 Developers List <linux-ext4@...r.kernel.org>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        Jeff Layton <jlayton@...hat.com>,
        "Joshua D. Drake" <jd@...mandprompt.com>
Subject: Re: fsync() errors is unsafe and risks data loss

On Wed, Apr 11, 2018 at 07:32:21PM -0700, Andres Freund wrote:
> 
> Most of that sounds like a good thing to do, but you got to recognize
> that that's a lot of linux specific code.

I know it's not what PG has chosen, but realistically all of the other
major databases and userspace based storage systems have used DIO
precisely *because* it's the way to avoid OS-specific behavior or
require OS-specific code.  DIO is simple, and pretty much the same
everywhere.

In contrast, the exact details of how buffered I/O workrs can be quite
different on different OS's.  This is especially true if you take
performance related details (e.g., the cleaning algorithm, how pages
get chosen for eviction, etc.)

As I read the PG-hackers thread, I thought I saw acknowledgement that
some of the behaviors you don't like with Linux also show up on other
Unix or Unix-like systems?

						- Ted