Re: PostgreSQL's handling of fsync() errors is unsafe and risks data loss at least on XFS

On 04/09/2018 04:00 AM, Craig Ringer wrote:
> On 9 April 2018 at 07:16, Andres Freund <andres(at)anarazel(dot)de
> <mailto:andres(at)anarazel(dot)de>> wrote:
>  
>
>
> I think the danger presented here is far smaller than some of the
> statements in this thread might make one think.
>
>
> Clearly it's not happening a huge amount or we'd have a lot of noise
> about Pg eating people's data, people shouting about how unreliable it
> is, etc. We don't. So it's not some earth shattering imminent threat to
> everyone's data. It's gone unnoticed, or the root cause unidentified,
> for a long time.
>

Yeah, it clearly isn't the case that everything we do suddenly got
pointless. It's fairly annoying, though.

> I suspect we've written off a fair few issues in the past as "it'd
> bad hardware" when actually, the hardware fault was the trigger for
> a Pg/kernel interaction bug. And blamed containers for things that
> weren't really the container's fault. But even so, if it were
> happening tons, we'd hear more noise.
>

Right. Write errors are fairly rare, and we've probably ignored a fair
number of cases demonstrating this issue. It kinda reminds me the wisdom
that not seeing planes with bullet holes in the engine does not mean
engines don't need armor [1].

[1]
https://medium.com/@penguinpress/an-excerpt-from-how-not-to-be-wrong-by-jordan-ellenberg-664e708cfc3d

regards

--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services