Optimize RocksDB Configuration

[willmeister]

We may be able to configure RocksDB that would lead to better performance in our specific setup. Determine if this is feasible and do so if it is.

[willmeister]

We should define the following config options:

• max_open_files right now, syncing will randomly fail when rocksdb opens more files than the filesystem allows
• total_threads number of background threads used for flushing and compaction

Might also suggest looking into I/O- and/or memory-specific configuration