Re: silent data loss with ext4 / all current versions

On 11/29/2015 03:33 PM, Tomas Vondra wrote:
> Hi,
>
> On 11/29/2015 02:38 PM, Craig Ringer wrote:
>>
>> I've had a few tries at implementing a qemu-based crashtester where it
>> hard kills the qemu instance at a random point then starts it back up.
>
> I've tried to reproduce the issue by killing a qemu VM, and so far I've
> been unsuccessful. On bare HW it was easily reproducible (I'd hit the
> issue 9 out of 10 attempts), so either I'm doing something wrong or qemu
> somehow interacts with the I/O.

Update: I've managed to reproduce the issue in the qemu setup - I think
it needs slightly different timing due to the VM being slightly slower.
I also tweaked vm.dirty_bytes and vm.dirty_background_bytes to values
used on the bare hardware (I suspect it widens the window).

regards

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