2nd order data atomicity failure

[dcousens]

If a system failure occurs during writing of the 2nd order data (e.g out of memory/space), then upon resume the 2nd order data is skipped due to the tip update not rolling back.

[dcousens]

Should we roll back the block if the 2nd order data fails to insert?

Its the only sane solution at this point...

[dcousens]

Alternatively, and this would support other use cases... we maintain two tips, one for 1st order data which can be directly imported in a fast-dat-parser run, and the other tip, for the 2nd order data...

Opening this up for discussion in #26

[dcousens]

Closing in favour of #26