Hot backup and fault tolerance limitations

[evoskuil]

The blockchain store is intended to support hot backup and to be tolerant of hard shutdown (during write) faults. Due to the speed and limited amount of writes, this is generally the case, but it is not guaranteed by the implementation.

The two scenarios rely on the store always existing in a consistent state. However there are multiple indexes in distinct files. Writes across these files are not atomic and therefore these scenarios may result in a partial update. The implementation is unable to detect this corruption, as each file individually remains consistent.

[evoskuil]

Moved to libbitcoin-database: libbitcoin/libbitcoin-database#16