At present, checkpoint_segment=3 checkpoint_timeout=300
I'd recommend at least setting checkpoint_segments to 12 and you might want to increase checkpoint_timeout too, although not too high. Maybe try doubling it.
And as Devrim pointed out, pre-8.3 versions suffer from these problems more, and 8.1 will cease to be supported in the near future, so if you're able to, upgrade. :)