* kvdb-rocksdb: update to RocksDB 5.8.8
* kvdb-rocksdb: tune RocksDB options
* Switch to level-style compaction
* Increase default block size (16K), and use bigger blocks for HDDs (64K)
* Increase default file size base (64MB SSDs, 256MB HDDs)
* Create a single block cache shared across all column families
* Tune compaction settings using RocksDB helper functions, taking into account
memory budget spread across all columns
* Configure backgrounds jobs based on the number of CPUs
* Set some default recommended settings
* ethcore: remove unused config blockchain.db_cache_size
* parity: increase default value for db_cache_size
* kvdb-rocksdb: enable compression on all levels
* kvdb-rocksdb: set global db_write_bufer_size
* kvdb-rocksdb: reduce db_write_bufer_size to force earlier flushing
* kvdb-rocksdb: use master branch for rust-rocksdb dependency
* created the dir crate in util
* moved code from ethstore/src/dir/paths.rs to dir crate
* rename dir module in ethstore to accounts_dir to distinguish it
from the dir crate
* changes after @tomusdrw on #6952
* parity-version module split from util
removed unused util deps and features
trigger buildbot again
only kvdb links rocksdb
snappy linker issues
* rm snappy
* fixed old version imports
Firstly, `Step.duration_remaining` casts it to u32, unnecesarily
limiting it to 2^32. While theoretically this is "good enough" (at 3
seconds steps it provides room for a little over 400 years), it is
still a lossy way to calculate the remaining time until the next step.
Secondly, step duration might be zero, triggering division by zero
in `Step.calibrate`
Solution: rework the code around the fact that duration is
typically in single digits and never grows, hence, it can be represented
by a much narrower range (u16) and this highlights the fact that
multiplying u64 by u16 will only result in an overflow in even further
future, at which point we should panic informatively (if anybody's
still around)
Similarly, panic when it is detected that incrementing the step
counter wrapped around on the overflow of usize.
As for the division by zero, prevent it by making zero an invalid
value for step duration. This will make AuRa log the constraint
mismatch and panic (after all, what purpose would zero step duration
serve? it makes no sense within the definition of the protocol,
as finality can only be achieved as per the specification
if messages are received within the step duration, which would violate
the speed of light and other physical laws in this case).
